statisticalrethinkin..

280 11. COUNTING AND CLASSIFICATIONthe other side had food only on the side close to the focal animal. ink of the prosocialoption as being 1/1, indicating food on both sides. e nonsocial option, in contrast, wasalways 1/0, indicating food only on the focal side. If the focal animal pulled the lever on the1/1 side, both animals received food. If he or she instead pulled the 1/0 lever, only the pullerreceived food. e side of the 1/1 option was balanced across trials, to control for handednesspreferences. So the first question to ask of these data will be: do the chimpanzees prefer the1/1 option?e second key treatment variable is whether or not another chimpanzee sat on the otherside of transparent divider. is is the condition dummy variable, with 1 indicating therewas another chimpanzee present. So the second question to ask of the data will be: do chimpanzeesprefer the 1/1 option more when another animal is present? Or are they insteadindifferent to the presence of the conspecific?To address these questions, we will try to predict which side the focal animal pulls, conditionalon which side had the 1/1 option and whether or not another animal was present.Since the outcome is binary (le or right lever), we’ll use a binomial stochastic node andbuild a GLM with a logit link. Load the data from the rethinking package:R code11.1library(rethinking)data(chimpanzees)d