Additional file 1: Table S1.

Results of online surveys to define ‘altruistic’ behaviours. Items originally proposed as potentially altruistic traits and how they were scored by respondents to an online survey of a) 72 women with a mean age of 24.0±3.25 years, and b) 89 men with a mean age of 23.8±4.08 years. Survey respondents were asked the following: “In your opinion, are the following activities altruistic? Please rate each activity from 1–5, where 1 = not at all altruistic and 5 = very altruistic.” Responses to each item were analysed for skewness and items which did not show significant negative skew (p ≥ 0.05) were dropped from the list and not used inteh experiment. Items which had a modal rating of <4 were also dropped (no item had a mode of 5). Items dropped from the list are highlighted in grey. This left 20 items which we classed as altruistic for females and 12 for males. Internal consistency was assessed using Cronbach’s alpha. This measures the extent to which a set of variables measures a single, unidimensional underlying construct. Our values of alpha were high (0.99 for 20 items seen as altruistic by females and 0.94 for 12 items seen as altruistic by males), suggesting that the responses to different activities were consistent.

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Moore et al. BMC Evolutionary Biology 2013 13:182   doi:10.1186/1471-2148-13-182