Fasolt V, Holzleitner IJ, Lee A, O'Shea KJ & DeBruine LM (2019). Methods comparison in third party kin recognition; or how everyone finds a different answer to the same question. International Society for Human Ethology in Zadar..

Research on third-party kin recognition has consistently found that humans can reliably judge relatedness among strangers when presented with face photographs alone. However, contrasting results have been found when looking at the effect of sex and age of the portrayed individuals on kinship judgments. This discrepancy could partially be due to the use of different methods. To explore this issue, we conducted a study implementing three commonly used methods (i.e., kinship judgment, similarity rating, matching), directly comparing the performance of participants across these methods using the same highly-controlled stimulus set for all of them. We found that while responses on all three methods were correlated, performance varied significantly across the tasks. Participants in the kinship judgment method were most accurate at detecting unrelated pairs, participants in the matching method were most accurate at detecting related pairs, and participants in the similarity rating method were equally good at detecting related and unrelated pairs. Furthermore, when looking at the effect sex and age of the portrayed individuals had on performance, we found that stimuli sex only had a main effect in the kinship judgment paradigm. Raters judged same-sex pairs to be related more often than opposite-sex pairs, independent of actual relatedness. In the matching method, there was an interaction between stimuli sex and stimuli age, where a larger age difference between stimuli decreased relatedness judgments for same sex pairs, but marginally increased relatedness judgments for opposite sex pairs. Our results suggest that different answers to the same question can be found, depending on which method is used. This highlights the need for standardised methods in the field to allow for valid and generalizable conclusions. Pre-registration, data and code are available on the Open Science Framework (https://osf.io/a3t8x/).

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