To examine the impact of group size on conformity behavior, phil o'dendron has groups of two, five, or ten people stand on a city street and stare up at a window. phil then records the number of passersby who stop and stare up. this study is an example of a(n):

The correct answer is an experimental study with one independent variable. 

This study is an experimental study because it involves investigating a causal relationship between two phenomena. In this study the researcher is investigating the relationship and checking for causality between the size of a group, and its effect on conformity behavior. This study furthermore has an independent variable (i.e. a variable that is manipulated and controlled) which is the size of the group of people staring up at a window.