Socioeconomic inequalities in health among elderly people in Taiwan: A life course perspective

Hsiao-Hsiao Tan; Yi-Chan Lee; Ya-Mei Chen; Tung-liang Chiang

doi:10.1371/journal.pone.0327191

Peer Review History

Original SubmissionJune 29, 2024
Decision Letter - Muhammad Fawad, Editor Dear Dr. Tan, Please submit your revised manuscript by Sep 28 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. 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Additional Editor Comments: I have some suggestions to further improve the manuscript. 1.The authors should explain how categorizing all participants who were "lost to follow-up" as part of the unhealthy group might affect the study's conclusions. Could this approach lead to an overestimation of the association between socioeconomic status and poor health outcomes? 2.How reliable is it to use a father's education as the only indicator of childhood socioeconomic status? Are there other measures that could provide a more comprehensive understanding of childhood socioeconomic status? 3.How do the observed cohort effects influence the interpretation of the cumulative socioeconomic status on health outcomes? Additionally, how generalizable are these findings to other populations or younger cohorts? 4.The manuscript contains several grammatical mistakes, specifically on Page# 6, Line 89, Page# 7, Line 114, Page #10, Line 158, and Page# 17, Line 205. I highly recommend conducting a thorough proofread to correct these errors and improve its overall clarity and readability. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? Reviewer #1: Yes Reviewer #2: Partly ******** 2. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #1: Yes Reviewer #2: No ****** 3. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #1: Yes Reviewer #2: Yes ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #1: No Reviewer #2: Yes ****** Reviewer #1: This study examines the relationships between socioeconomic status (SES) at different life stages and health outcomes in old age, using data from the Taiwan Longitudinal Study on Aging (TLSA). The authors analyze three SES indicators across the life course: father's education (childhood SES), participant's education (early adulthood SES), and monthly household income (late adulthood SES). They assess three health outcomes: self-rated health, ADL disability (bathing only), and IADL disability. The study employs Generalized Estimating Equations (GEE) models to investigate longitudinal patterns and the cumulative effects of SES on health outcomes. Some Suggestions: 1-Clarify the specific research questions or hypotheses in the introduction. 2-would it be possible to Consider exploring potential mediating factors between SES and health outcomes, such as health behaviors or access to healthcare? 3-The study does not address potential reverse causality between SES and health, which could be particularly relevant for late adulthood SES (income) and health outcomes. Reviewer #2: This study explores the relationship between socioeconomic status (SES) and health among elderly Taiwanese individuals. The manuscript addresses a relevant topic. However, after a careful reading, I have identified some areas that could be improved to enhance the clarity and quality of the manuscript. METHODS The Methods section is well-structured but could benefit from additional clarity and detail, especially regarding variables and analytical procedures. Suggestions include: 1.1. Describe the study design. 1.2. Detail how the SES variables were categorized and justify these choices. Also, describe how adjusted variables were collected and categorized. 1.3. Explain in more detail the ‘hot-deck’ imputation method used for handling missing data. Cite a reference for this technique from the scientific literature as well. 1.4. Provide more details about the choice of Generalized Estimating Equations (GEE) models, specifying the type of regression used (Poisson, Logistic, Negative Binomial ...). Also, detail the level of aggregation, wicth probably is the year or the wave. 1.5. Provide a figure with the model of Analysis Planning for variables organization (DAG - Directed Acyclic Graph). 1.6. Provide more details about the sampling process and the sample size calculation performed. RESULTS The Results section does not present the findings clearly and can be improved with more detail and structure. 2.1. Specify the demographic characteristics of the participants in the different waves, as well as response rates and follow-up losses. For example: “Of the initial 4,049 participants, 60% were women, and the average age was 70 years at baseline. In 2003, 1,743 participants remained, with a response rate of approximately 90% in subsequent waves.” 2.2. Provide a flowchart of the sample for each wave. 2.3. Create a first table with the sample description stratified by waves (five waves) and include the education variable in the row, as well as the other variables in the study. 2.4. Tables are not self-explanatory. Reorganize the columns or rows, as it is currently not possible to verify the reference categories in the regressions models. DISCUSSION 3.1. Avoid being too emphatic in stating that the observed gradients in outcomes are due to cumulative effects, as the study design does not permit this conclusion. Clarify whether this is a cross-sectional or longitudinal cohort study. If the study followed the same individuals from 1989 onwards, it is a cohort study. However, if new individuals were included in each wave, it is cross-sectional, and the waves are time series that can be aggregated using GEE, but these are not cumulative effects, even if parental data were used. Please clarify this point. 3.2. What are the other individual and contextual possible confounding factors not addressed in this study but that might affect the results? 3.3- Discuss the aging process in more detail. 3.4. Similarly to the beginning of the discussion, reconsider the conclusion as it is currently too emphatic and deterministic, which might be biased due to the lack of methodological clarifications still needed. I believe that with the suggested improvements, the manuscript will make a significant contribution to the literature on the relationship between SES and health among the elderly. I am available for further reviews and hope that my suggestions will help strengthen the article. Regards. ****** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy Reviewer #1: Yes: Elham Faghihzadeh Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org . Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0327191.r001
Revision 1
4 Oct 2024 Author Response 【Editor Comments】 1. The authors should explain how categorizing all participants who were "lost to follow-up" as part of the unhealthy group might affect the study's conclusions. Could this approach lead to an overestimation of the association between socioeconomic status and poor health outcomes? Response: Thank you for noting that the overestimation of unhealthy data might have resulted from classifying all “lost to follow-up” individuals as unhealthy. We conducted sensitivity analyses to investigate the health outcomes with varying proportions of “lost to follow-up” individuals classified as unhealthy. These analyses were included in the statistical analyses section of the methods on Page# 11, Line 181 of the revised manuscript, with results concluded on Page# 23, Line 259 and the table results detailed in S1 File. In the sensitivity analyses, we randomly assigned 80% and 90% of individuals “lost to follow-up” as unhealthy, and also tested the outcome when all lost to follow-up individuals were classified as missing. Comparing the sample size of those lost to follow-up with mortality count data from the 2007 TLSA research report, the calculated mortality rate among individuals classified as “lost to follow-up” across five study waves ranged from 83.9% to 92.5%. The comparative data are presented in Table 1. Table 1 Mortality rates among participants classified as “lost to follow-up” across five waves In addition, in cohort studies, participants lost to follow-up are rarely lost randomly (Kristman et al., 2004). Studies have found that individuals lost to follow-up tend to belong to lower socioeconomic status groups and experience more health problems, whether these differences are statistically significant or not (Hoeymans et al., 1998; Launer et al., 1994; Mihelic & Crimmins, 1997; Norris, 1985). The sensitivity analyses yielded similar results to the study. Health outcomes were better for participants with higher socioeconomic status accumulation across three life stages. The magnitude of the results for the 80% and 90% scenarios was attenuated, yet the overall associations and patterns remained stable. The findings from all participants lost to follow-up, categorized as missing, demonstrate an even more pronounced effect on SES accumulation, although they exhibit significant fluctuations and instability. This limitation has been covered in the discussion section; please refer to Page# 28, Line 351 in the revised manuscript. 2. How reliable is it to use a father's education as the only indicator of childhood socioeconomic status? Are there other measures that could provide a more comprehensive understanding of childhood socioeconomic status? Response: We are grateful for your reminder to explore other indicators of childhood SES. Common indicators of childhood SES include household income, and the education and occupation of both parents (Bradley & Corwyn, 2002; Kaplan et al., 2001). In the TLSA, data on mothers' socioeconomic status (SES) and childhood household income were not collected, while information on fathers' education and occupation was. By using fathers’ occupation as a measure of childhood SES, we conducted the GEE analysis and found similar results. Please see the results in Table 4-6 at the end of this answer of this question. Earlier studies often emphasize fathers’ SES, as women's access to education and formal employment has increased only in more recent decades, and childhood household income is prone to recall bias when participants are asked to report it. Therefore, we have selected the father’s education and occupation as the indicators representing childhood SES. Table 2 is the comparative table of sample numbers stratified by fathers’ education and occupation as indicators. Table 2 Comparative sample sizes stratified by fathers’ education and occupation The data reveal that SES from a preceding stage has a considerable effect on SES in the next stage, with large fluctuations in SES trajectories being rare. Moreover, a higher number of individuals with the most advantaged adulthood SES had literate fathers compared to those with white-collar fathers. The correlation coefficients for each indicator are presented in Table 3. According to Table 3, fathers’ education exhibits a higher correlation with all indicators in comparison to fathers’ occupation. As education serves not only as an indicator of SES but also as a precursor to occupation and income (Liberatos et al., 1988), we used fathers’ education as the proxy for childhood SES instead of occupation. Table 3 Spearman correlation coefficients for SES indicators and baseline health outcomes Table 4 GEE analysis of self-rated health (SRH): odds ratios (95% confidence intervals) across three life stages’ SES strata Table 5 GEE analysis of ADL disability (bathing only): odds ratios (95% confidence intervals) across three life stages’ SES strata Table 6 GEE analysis of IADL disability: odds ratios (95% confidence intervals) across three life stages’ SES strata 3. How do the observed cohort effects influence the interpretation of the cumulative socioeconomic status on health outcomes? Additionally, how generalizable are these findings to other populations or younger cohorts? Response: Thank you for pointing this out. We conducted a GEE analysis by separating participants into two pseudo-cohort groups to observe cohort effects, and found consistent results. Greater accumulation of SES is often linked to superior health outcomes. Please see the results in Table 7-8. Results for the younger pseudo-cohort remain similar and are reinforced. Conversely, the older pseudo-cohort model is quite unstable. Hence, we conducted another GEE analysis, where all individuals lost to follow-up were classified as missing, as shown in Table 9. The results were akin to those in Table 8. Additionally, Table 10 displays the distribution of the older pseudo-cohort stratified by three SES indicators. It is observed that the survival rate increases with higher SES accumulation. Nevertheless, as reported by the Ministry of the Interior, the average life expectancy in Taiwan was 73.4 years in 1989 and 77.0 years in 2003. Eighty percent of the participant population was lost to follow-up, which might explain the model’s instability. While we recognize the importance of this consideration, the cohort effect is unavoidable and cannot be analyzed in this manuscript because the dataset lacks sufficient variability. Cumulative effects have been demonstrated in previous studies (Smith et al., 1997), and we observed similar findings in this study, where individuals with more advantaged SES tended to exhibit better health. Despite the fact that contemporary populations generally have higher levels of educational attainment, similar outcomes should be expected, provided that health continues to be shaped by SES. These findings may be generalizable to more advanced studies. This limitation has been addressed in the discussion section, please refer to Page# 27, Line 331 in the revised manuscript. Table 7 GEE analysis of SRH: odds ratios (95% confidence intervals) across three life stages’ SES strata (participants aged 60-69 years) Table 8 GEE analysis of SRH: odds ratios (95% confidence intervals) across three life stages’ SES strata (participants aged 70-96 years) Table 9 GEE analysis of SRH: odds ratios (95% confidence intervals) across three life stages’ SES strata (participants aged 70-96 years and all lost to follow-up individuals are excluded) Table 10 Population size of the older pseudo-cohort stratified by three SES indicators 4. The manuscript contains several grammatical mistakes, specifically on Page# 6, Line 89, Page# 7, Line 114, Page #10, Line 158, and Page# 17, Line 205. I highly recommend conducting a thorough proofread to correct these errors and improve its overall clarity and readability. Response: Thank you for your suggestions. We have carefully revised the manuscript to enhance overall clarity and readability, and to correct grammatical errors. Please find the revised manuscript enclosed. Here are the corrections for the specific points you mentioned: Page# 6, Line 89 > Page# 6, Line 103 Origin: “Out of the initial 4,049 participants, only 1,743 remained in the study during the 2003 survey, with 2,306 lost to follow-up.” Correct: “Of the initial 4,049 participants, 1,743 were retained in the study for the 2003 survey, while 2,306 were lost to follow-up.” Page# 7, Line 114 > Page# 8, Line 137 Origin: “Monthly household income levels of respondents were classified into three categories: low, medium, and high.” Correct: “Respondents' monthly household income levels were categorized into three strata: low (< 3,000 NTD), medium (3,000-19,999 NTD), and high (≥ 20,000 NTD).” Page #10, Line 158 > Page# 12, Line 199 Origin: “Generally, populations with more advantageous SES characteristics tend to exhibit better overall health, even after adjusting for demographic factors and baseline health.” Correct: “Generally, populations characterized by more advantageous SES tend to exhibit better overall health outcomes, even after controlling for demographic factors and baseline health.” Page# 17, Line 205 > Page# 22, Line 236 Origin: “Still, superior early and late adulthood SES significantly reflects a lesser decline in health.” Correct: “Yet, the rate of decline is influenced by SES accumulation, with increased SES accumulation significantly associated with a lesser decline in health.” 【Reviewer #1】 1- Clarify the specific research questions or hypotheses in the introduction. Response: Thank you for pointing this out. The research hypotheses presented in the introduction have been revised as follow. Please also refer to Page# 5, Line 83 in the revised manuscript. “The purpose of this study is to investigate how health trajectory in old age is shaped by the accumulation of socioeconomic status across three life stages.” 2- would it be possible to Consider exploring potential mediating factors between SES and health outcomes, such as health behaviors or access to healthcare? Response: Thank you for highlighting this. While we agree that this is an important consideration, it is beyond the scope of this manuscript. This study examines the impact of SES on health, considering that the small size of subgroup samples could limit further analysis of mediating effects. The correlation coefficients for SES indicators, health behaviors, and baseline health outcomes are presented in Table 11. Table 11 reveals that health behaviors exhibit a mild correlation with all other indicators, which may pose challenges for the analysis of mediating effects. Table 11 Spearman correlation coefficients for SES indicators, health behaviors, and baseline health outcomes As the mediating effect of health behaviors and psychosocial characteristics is well-documented (Lynch et al., 1997; Macintyre, 1997), our study is specifically aimed at examining the direct relationship between SES and health. 3- The study does not address potential reverse causality between SES and health, which could be particularly relevant for late adulthood SES (income) and health outcomes. Response: Thank you for highlighting this. While we agree that this is an important consideration, it is beyond the scope of this manuscript due to the need for advanced analytical methods or the inclusion of additional variables. The effect of health on SES is acknowledged but was not included in our study. The issue of bidirectional causality has been acknowledged since the 1980s, as noted in the Black Report. Table 12 displays the correlation coefficients for SES indicators and baseline health outcomes. While late adulthood SES is significantly related to three health indicators, the effects are weaker than those from early adulthood SES (education), as education represents more than just an SES indicator. Moreover, most prior research has concentrated on how SES affects health rather than the reverse, as the impact of health on SES is relatively minor compared to the impact of SES on health. We used an early-life health indicator as an example to test the correlation and found similar results. An indicator of early life health is included in Table 12. The health indicator at age 16 was measured in 2003, as it was not surveyed in 1989. Consequently, those lost to follow-up are all classified as unhealthy, potentially leading to an overestimation of early-life unhealthiness. Table 12 reveals the minor yet significant impact of early-life health on SES and health in later life. Our research is limited to examining the effect of SES on health, whilst acknowledging that early-life health can have a minor but profound impact on later-life SES and health (Blane et al., 1993; Haas, 2008; Haas, 2006; West, 1991). The intricate nature of the SES-health relationship makes it difficult to fully disentangle all the interconnections. Our study focuses on examining the direct relationship between SES and health. Table 12 Spearman correlation coefficients for SES indicators and health outcomes 【Reviewer #2】 METHODS The Methods section is well-structured but could benefit from additional clarity and detail, especially regarding variables and analytical procedures. Suggestions include: 1.1. Describe the study design. Response: Thank you for your suggestions. The study design has been added to the revised manuscript; please see Page# 7, Line 117. “This study aims to explore how cumulative exposure to socioeconomic status (SES) at different life stages shapes health trajectories in later life. SES data were collected in the baseline year, and health trajectories were analyzed using Generalized Estimating Equations (GEE). This design allowed for the examination of baseline health and subsequent changes over time.” 1.2. Detail how the SES variables were categorized and justify these choices. Also, describe how adjusted variables were collected and categorized. Response: The three chosen SES indicators are as follows. This study utilized SES indicators across three life stages: childhood, early adulthood, and late adulthood. These indicators included the educational attainment of participants' fathers, the participants' own educational attainment, and monthly household income. The revised version is included on Page# 8, Line 137 of the updated manuscript. Regarding father’s education, most participants’ fathers from that era had limited access to schooling. This provided an opportunity to examine the health effects of parental education on their offspring, specifically whether the parent received education or not. In the dataset, approximately half of the fathers were literate, while the other half were not. Educational opportunities improved over time, allowing us to divide participants’ education levels into three categories to capture health disparities between the more advantaged and disadvantaged groups. A similar rationale was applied to income categorization to enhance the visibility of health differences. The 1989 survey collected data on participants’ monthly household income, categorized as: (1) less than 3,000 NTD, (2) 3,000-4,999 NTD, (3) 5,000-9,999 NTD, (4) 10,000-14,999 NTD, (5) 15,000-19,999 NTD, (6) 20,000-49,999 NTD, and (7) above 50,000 NTD. According to Taiwan’s Ministry of Health and Welfare, the minimum living wage in 1991 was 3,000 NTD. The Directorate-General of Budget, Accounting and Statistics, Executive Yuan, reported an average salary of 21,247 NTD in 1989. Therefore, we used 3,000 NTD and 20,000 NTD as cut points to divide participants into three income groups: low (< 3,000 NTD), medium (3,000-19,999 NTD), and high (≥ 20,000 NTD). Recognizing the importance of sociodemographic characteristics in determining health, gender and age were included as covariates. The age range of participants was 60 to 96 years. They were classified into five groups, each with a five-year interval starting at age 60, with the last group including those aged 80 and above. This study aims to examine how the accumulation of SES across three life stages informs both baseline health and subsequent health changes. Therefore, baseline health was also controlled for. Attachments Attachment Submitted filename: response to reviewers.docx https://doi.org/10.1371/journal.pone.0327191.r002
Decision Letter - Muhammad Fawad, Editor Dear Dr. Tan, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Mar 07 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols . We look forward to receiving your revised manuscript. Kind regards, Muhammad Fawad, PhD Academic Editor PLOS ONE Journal Requirements: Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author Reviewer #3: (No Response) ******** 2. Is the manuscript technically sound, and do the data support the conclusions??> Reviewer #3: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #3: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #3: (No Response) ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #3: (No Response) ****** Reviewer #3: Editor Comments 1. Categorizing "lost to follow-up" participants as unhealthy • The authors should extend their sensitivity analysis to include a broader range of scenarios (e.g., 30%, 50%, 70%). This would better demonstrate the robustness of their conclusions across varying assumptions about the health status of those lost to follow-up. • The authors could conduct an analysis comparing the SES variables of those lost to follow-up with those who remained in the study. This is an effective way to provide empirical support for the assumption that individuals lost to follow-up tend to have worse SES. 2. Cohort effects and generalizability of findings • Response: The authors addressed cohort effects through analyses of pseudo-cohorts and discussed the limitations of dataset variability. • Recommend that the authors include age as a time-varying covariate in their Generalized Estimating Equations (GEE) model. This would allow them to better differentiate between the effects of biological aging and cohort effects. Reviewer #2’s Comment 1- Study design and methodological clarifications It could be improved with more detail and clarity about the study’s design and methodology such as whether this is a cohort study or explain key design elements, such as the timeline, follow-up intervals and a brief description of how participants were recruited and followed over time. 2- Detail about SES variables: Why did not authors use methods like Principal Component Analysis (PCA) to extract a single composite SES variable? 3-Results I could not find any changes regarding comment 2.1 in the manuscript, or I may be missing something. ****** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy Reviewer #3: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/ . PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org https://doi.org/10.1371/journal.pone.0327191.r003
Revision 2
7 Mar 2025 Author Response Our heartfelt thanks go to the editor and reviewers. Your thoughtful questions have inspired us to delve deeper into our analysis and improve our explanations. Attachments Attachment Submitted filename: response_to_reviewers_auresp_2.docx https://doi.org/10.1371/journal.pone.0327191.r004
Decision Letter - Sreeram V. Ramagopalan, Editor Dear Dr. Tan, Please submit your revised manuscript by Jun 11 2025 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'. A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'. An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'. If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols . Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols . We look forward to receiving your revised manuscript. Kind regards, Sreeram V. Ramagopalan Academic Editor PLOS ONE Journal Requirements: Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author Reviewer #3: (No Response) Reviewer #4: All comments have been addressed ******** 2. Is the manuscript technically sound, and do the data support the conclusions??> Reviewer #3: Yes Reviewer #4: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? -->?> Reviewer #3: Yes Reviewer #4: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available??> The PLOS Data policy Reviewer #3: (No Response) Reviewer #4: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English??> Reviewer #3: (No Response) Reviewer #4: Yes ****** Reviewer #3: (No Response) Reviewer #4: Does the study design sufficiently account for potential biases introduced by the loss of follow-up participants? It may benefit from a more direct explanation of how these objectives specifically relate to the study's aims regarding socioeconomic status (SES) and health trajectories. The exclusion of mountainous areas merits more justification. How might this exclusion impact the generalizability of the findings? Lines 127-129: Please provide more details regarding the reasons for participant attrition. Were there common factors among those lost to follow-up that could introduce selection bias? Lines 160-167: Consider adding context about the significance of the chosen income categories. How do these thresholds correlate with the economic context of Taiwan during the relevant years? Lines 172-185: While the selection of health indicators appears rational, the focus on bathing as an Activities of Daily Living (ADL) measure seems somewhat narrow. Please justify the choice of bathing over other potential indicators, such as eating or dressing. The abbreviations for TLSA, SES, and others were not introduced in Figure 1 and Tables. Please clarify these terms for better understanding. Regarding the Self-Rated Health (SRH) question with a 5-point Likert scale, which specific points were considered indicative of "good" health? ****** what does this mean? ). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. 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Revision 3
10 Jun 2025 Author Response � Does the study design sufficiently account for potential biases introduced by the loss of follow-up participants? It may benefit from a more direct explanation of how these objectives specifically relate to the study's aims regarding socioeconomic status (SES) and health trajectories. Response: We appreciate your reminder. The constraints inherent in this study restricted the ability to achieve a fully robust design. Given that the majority of participants lost to follow-up were deceased, they were categorized as unhealthy to better analyze the association between socioeconomic status (SES) and health trajectories. Comprehensive sensitivity analyses were conducted to ensure the stability and reliability of the data. Comparing the sample size of those lost to follow-up with mortality count data from the 2007 TLSA research report, the calculated mortality rate among individuals classified as “lost to follow-up” across five study waves ranged from 83.9% to 92.5%. The comparative data are provided in Table 1 for further reference. Table 1 Mortality rates among participants classified as “lost to follow-up” across five waves � The exclusion of mountainous areas merits more justification. How might this exclusion impact the generalizability of the findings? Response: We appreciate your reminder. The relationship between SES and health is firmly established. Moreover, the multifaceted interactions both within various SES dimensions and between SES and health exhibit considerable complexity. This study aimed to further explore this relationship by elucidating the connections between SES at three distinct life stages and later health trajectories. The health gradients were examined from multiple perspectives. An interesting observation emerged, which may merit further exploration. These findings may be generalizable to more advanced studies. � Lines 127-129: Please provide more details regarding the reasons for participant attrition. Were there common factors among those lost to follow-up that could introduce selection bias? Response: Thank you for pointing this out. As shown in Table 1, the majority of participants lost to follow-up were deceased, while the remaining individuals either declined participation, were repeatedly untraceable, or lost contact entirely. Nonetheless, in each wave, only approximately 10% of the remaining participants were not included in the investigation. This survey was conducted under the coordination of the Health Promotion Administration, Ministry of Health and Welfare, and benefited significantly from local authorities' assistance. The reliability of the data was ensured despite certain losses. However, in cohort studies, participants lost to follow-up are rarely lost randomly (Kristman et al., 2004). Studies have found that individuals lost to follow-up tend to belong to lower socioeconomic status groups and experience more health problems, whether these differences are statistically significant or not (Hoeymans et al., 1998; Launer et al., 1994; Mihelic & Crimmins, 1997; Norris, 1985). The remaining participants generally have higher SES, potentially leading to selection bias. While we acknowledge the significance of this factor, the loss of participants was inevitable. Despite the fact, similar outcomes should be expected, provided that health continues to be shaped by SES. � Lines 160-167: Consider adding context about the significance of the chosen income categories. How do these thresholds correlate with the economic context of Taiwan during the relevant years? Response: The 1989 survey collected data on participants’ monthly household income, categorized as: (1) less than 3,000 NTD, (2) 3,000-4,999 NTD, (3) 5,000-9,999 NTD, (4) 10,000-14,999 NTD, (5) 15,000-19,999 NTD, (6) 20,000-49,999 NTD, and (7) above 50,000 NTD. According to Taiwan’s Ministry of Health and Welfare, the minimum living wage in 1991 was 3,000 NTD. The Directorate-General of Budget, Accounting and Statistics, Executive Yuan, reported an average salary of 21,247 NTD in 1989. Therefore, we used 3,000 NTD and 20,000 NTD as cut points to divide participants into three income groups: low (< 3,000 NTD), medium (3,000-19,999 NTD), and high (≥ 20,000 NTD). � Lines 172-185: While the selection of health indicators appears rational, the focus on bathing as an Activities of Daily Living (ADL) measure seems somewhat narrow. Please justify the choice of bathing over other potential indicators, such as eating or dressing. Response: The ADLs include the following: “(1) Ambulating: The Extent of an individual's ability to move from 1 position to another and walk independently; (2) Feeding: The Ability of an individual to feed oneself; (3) Dressing: The ability to select appropriate clothes and to put them on; (4) Personal hygiene: The ability to bathe and groom oneself and maintain dental hygiene, nail, and hair care; (5) Continence: The ability to control bladder and bowel function; (6) Toileting: The ability to get to and from the toilet, use it appropriately, and clean oneself afterward” (Edemekong et al., 2025). In the 1989 interview, participants were asked about their ability to: (1) independently purchase daily necessities, such as soap, toothpaste, and medicine; (2) manage financial matters, including paying bills and handling change; (3) make phone calls; (4) maintain personal hygiene, specifically through bathing; (5) climb stairs; (6) walk a distance of 200–300 meters; (7) perform labor-intensive tasks, such as floor cleaning and agricultural work; (8) manage transportation, either by driving or arranging alternative modes; (9) lift objects weighing approximately 12 kg; (10) perform squatting movements; (11) raise arms above head level; (12) manipulate objects using fine finger movements; and (13) maintaining a standing position for a continuous duration of two hours. Due to the incomplete ADL data in the 1989 interview, only bathing was selected as the representative ADL indicator for this study. Nevertheless, in Taiwan, difficulty bathing is the most frequently cited limitation in ADL. Having persistent difficulties bathing is an independent risk of long-term nursing home admission (Gill et al., 2006). � The abbreviations for TLSA, SES, and others were not introduced in Figure 1 and Tables. Please clarify these terms for better understanding. Response: We appreciate your reminder. Kindly review the revised Figure 1, the updated Table 1, and the supporting information. � Regarding the Self-Rated Health (SRH) question with a 5-point Likert scale, which specific points were considered indicative of "good" health? Response: Thank you for pointing this out. For the purposes of this study, we designated "very good" and "good" health as "good," whereas the other three classifications were categorized as "poor" health, given our analytical focus on overall health status. Attachments Attachment Submitted filename: response_to_reviewers_auresp_3.docx https://doi.org/10.1371/journal.pone.0327191.r006
Decision Letter - Sreeram V. Ramagopalan, Editor <p>Socioeconomic inequalities in health among elderly people in Taiwan: a life course perspective PONE-D-24-26589R3 Dear Dr. Tan, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, please contact our Author Billing department directly at authorbilling@plos.org. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Sreeram V. Ramagopalan Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0327191.r007
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Acceptance Letter - Sreeram V. Ramagopalan, Editor PONE-D-24-26589R3 PLOS ONE Dear Dr. Tan, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, if your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. If we can help with anything else, please email us at customercare@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. Sreeram V. Ramagopalan Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0327191.r008

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