Peer Review History

Original SubmissionJanuary 24, 2020
Decision Letter - Tiago P. Peixoto, Editor

PONE-D-20-02223

Tubes and Bubbles - Topological Confinement of YouTube Recommendations

PLOS ONE

Dear Dr. Roth,

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.

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Kind regards,

Tiago P. Peixoto

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: In this manuscript the authors approach the problem of how filter bubbles in online social systems can emerge as a result of the underlying recommendation system. For this they investigate the structure of networks obtained from following recommendations across videos on youtube. Specifically, the authors create and validate a new methodology for collecting such data and perform a detailed computational analysis of the obtained networks finding that i) networks contract as the seed videos become more popular, and ii) the dynamics of the random walks exhibit confinement.

This work makes a substantial contribution to recent and ongoing efforts to better understand the dynamics in socio-technical systems such as youtube which have become a major platform for dissemination and consumption of information. I like the innovative methodological approach taken by the authors to look under the hood of these recommendation systems via recommendation networks (and the rigor in validating it), especially given the fact that the underlying algorithms&data are not openly accessible. The statistical anaylsis is solid and the results are presented in an intelligible way. My main point of criticism is on the interpretation of the results in terms of the dynamics (see details below). I think it should be clarified that all conclusions come from correlational analysis and not from following the dynamics of individual videos over time in order to avoid misunderstandings. Pending corresponding revision, I fully recommend publication of the paper.

1. The results of mean entropy and number of pageviews is described as a graph contraction (line 217): "It appears that, as videos receive views, their overall recommendation graphs contract, becoming significantly smaller in number of nodes, while the diversity of the mean random walk increases."

The results in Figure 4 suggest a strong correlation between entropy and number of views. However, the conslusion as written suggests a dynamical process of indivdual videos which would only be justifieds from longitudinal studies.

2. In line 253 the authors refer to "audience effect" - I am not aware of a clear definition and couldnt find one in the manuscript. Perhaps the authors could clarify in order to avoid misunderstanding on what is meant.

3. In line 257 the authors claim that the measure of c is an intrinsic property of the video bc it is not correlated with explicit actions. I think this statement is a bit too strong in the absence of following individual videos over time.

4. In line 278 the authors claim that the dynamics is dominantly driven by the actions of the user. The dataset does not follow the dynamics of a video over time.

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Reviewer #1: Yes: Martin Gerlach

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Revision 1

Dear Editor, Dear Reviewer,

We thank you for your consideration of our manuscript and are very pleased to have carried out the requested revision. We also fully agree with all the remarks of Reviewer 1, whom we wish to thank for his report on our work.

This revision attemps to improve the manuscript by taking into account all the issues that have been raised. In particular, we changed the wording related to the dynamics of recommendation graphs — it is true that confirming the contraction of these graphs over time because of user interaction would require a different protocol, where we would collect and study recommendation graphs in a longitudinal manner. In this respect, we amended our remarks to reflect the fact that we simply observed correlations between views and graph size and density, and that we cannot directly conclude on graph contraction, especially on pages 7, 8, 11 (previously 10), and 13.

We also added a clarification sentence regarding what we mean with “audience effect” on page 10 (previously 9), and toned down several claims identified by Reviewer 1. We further inserted two citations to two additional studies published in 2020 which feature the computation of diversity or confinement through random walks.

More broadly, we also took into account the general remark pertaining to our goals and to the framing of our work within the literature — we added sentences to this effect in the abstract, in the introduction, and in the conclusion. We hope that this further clarifies our positioning within the state of the art on the effects of algorithmic recommendation.

We finally added a precision regarding the respect of YouTube Terms of Service for the data collection operations. We mentioned the availability of our data and scripts in publicly-available repositories.

We emphasized all these changes by putting the text in blue where needed (for the sake of clarity, we however did not emphasize the very minor typo and form corrections).

We hope to have addressed all matters of concern regarding this manuscript in order to make it fit for publication. We nevertheless remain at your disposal to carry out further improvements.

Attachments
Attachment
Submitted filename: cover-letter-revision-including-response.pdf
Decision Letter - Tiago P. Peixoto, Editor

Tubes and Bubbles - Topological Confinement of YouTube Recommendations

PONE-D-20-02223R1

Dear Dr. Roth,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

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If your institution or institutions have a press office, please notify them about your upcoming paper to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, you must inform our press team as soon as possible and 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.

With kind regards,

Tiago P. Peixoto

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The revised manuscript addresses all the concerns raised in my previous comments substantially improving the manuscript. I recommend publication of the manuscript in PLOS ONE.

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7. PLOS authors have the option to publish the peer review history of their article (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: Martin Gerlach

Formally Accepted
Acceptance Letter - Tiago P. Peixoto, Editor

PONE-D-20-02223R1

Tubes and Bubbles Topological Confinement of YouTube Recommendations

Dear Dr. Roth:

I am pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please notify them about your upcoming paper at this point, to enable them to help maximize its impact. If they will be preparing press materials for this manuscript, 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.

For any other questions or concerns, please email plosone@plos.org.

Thank you for submitting your work to PLOS ONE.

With kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Tiago P. Peixoto

Academic Editor

PLOS ONE

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