Supplemental Section of Evaluating Patient’s Ability to Detect Changes in Hair Density Using Standardized Global Scalp Photography: A Cross-Sectional Study
Description
This is the Supplemental Section of the paper "Evaluating Patient’s Ability to Detect Changes in Hair Density Using Standardized Global Scalp Photography: A Cross-Sectional Study." This study aimed to define the threshold at which patients with and without alopecia perceive changes in hair density and compare these values to those of dermatologists. A validated survey method from Buontempo et al. was distributed to 205 participants (100 with alopecia, 105 without) from the NYU Skin and Cancer Clinic, NYU Faculty Group Practice, and via email (99% response rate). Participants evaluated 14 sets of standardized scalp photographs, identifying images with higher, lower, or unchanged hair density. A logistic regression model estimated the “just noticeable difference” (critical threshold) at 41.69 hairs/cm², corresponding to a 22.78% relative difference. This closely aligned with the previously reported dermatologist threshold of 20.66%. Welch’s t-test with Bonferroni correction revealed no significant differences in critical thresholds between participants with and without alopecia or between patients and dermatologists. This supplemental section specifically details how the survey was created and what parameters/questions the survey collected. It also illustrates the demographic breakdown of the survey participants, the critical thresholds for hair density detection across multiple subgroups, and the corresponding significant difference between these subgroups via tables. Lastly, the methodology for the literature search strategy and the python code used for the paper is described. These findings suggest that patients perceive hair density changes at a threshold comparable to dermatologists, indicating that subjective perception alone may be sufficient for detecting early hair loss. The lack of significant differences across subgroups suggests that personal experience with alopecia does not substantially alter perception. These results support the integration of trichometric data with photography for objective disease monitoring.