What are the observational units?

Social psychologists throughout the years have shown that an aggression–sexuality link exists not only in various animal species but also in humans. Dutton and Aron (Journal of Personality and Social Psychology, 1974) set out to show that a more general link exists in humans, namely emotional arousal of all kinds and sexual attraction. They set up their study to compare men in a high emotional arousal situation to men in a low emotional arousal situation. Researchers wanted to test the notion that an attractive female is seen as more attractive by males who encounter her in a fear-arousing situation than by males who encounter her in a non-fear-arousing situation. In the high emotional arousal group, men deemed to be between the ages of 18 and 35 who crossed a suspension bridge 230 feet above rocks and shallow rapids in Capilano Canyon, North Vancouver, British Columbia, Canada, and were not accompanied by a female were approached on the bridge by an attractive female interviewer. 

The same interviewer also approached men who fit the same criteria but crossed a solid wood bridge 10 feet above a rivulet that ran into the main river. Both groups of men were interviewed on the bridge and were told that the interview was for a psychology class project on the effects of exposure to scenic attractions on creative expression. The men filled out a short questionnaire, after which the interviewer wrote her phone number down on a slip of paper and said that if they were interested in the results of the experiment they could call her. The researcher talked to 18 men on the suspension bridge and 16 men on the wooden bridge.