Fig 1.
TREND flowchart of sampling process.
Fig 2.
Standardized bias plot of the covariates before and after propensity score matching.
The X-axis displays standardized percentage bias for each covariate, while the Y-axis lists the observed covariates. The standardized bias plot was used to assess covariate balance between the BCC-exposed and non-exposed groups before and after matching. The vertical reference line (red) on X-axis at ±10% standardized bias represents the accepted threshold for adequate covariate balance..
Fig 3.
Kernel density plots of propensity scores before and after matching.
X-axis: Propensity scores (range 0–1.0), and Y-axis: Kernel density (probability density of propensity scores). (A) Before matching: shows limited overlap between BCC-exposed and non-exposed (control) groups, (B) After matching: exhibits improved overlap in propensity scores, indicating better balance between groups.
Fig 4.
Distribution of dysmenorrhea pain grades by BCC exposure before and after propensity score matching.
Prevalence (%): percentage of participants reporting different dysmenorrhea pain grades (No pain, Mild, Moderate, and Severe) in BCC-exposed and non-exposed (control groups). (A) Shows the distribution of dysmenorrhea pain grades in the study groups before matching (𝛘2 = 168.01 and p < 0.001); (B) Demonstrates the distribution of dysmenorrhea pain grades in BCC-exposed and non-exposed (control) groups after matching (𝛘2 = 6.8 and p > 0.05).
Table 1.
Participant characteristics according to BCC-exposure status before and after propensity score matching.
Table 2.
Factors associated with dysmenorrhea according to BCC exposure status before and after propensity score matching using multivariable logistic regression.
Table 3.
Adjusted associations of BCC module exposure, key lifestyle factors, and dysmenorrhea before and after propensity score matching.
Table 4.
Adjusted differences in dysmenorrhea prevalence between BCC-exposed and non-exposed participants (ATT estimates).