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106 PART II: Descriptive Methodsbetween field experiments and other observational methods is that researchersexert more control in field experiments when they manipulate an independentvariable. Field experiments are frequently used in social psychology. For example,confederates have posed as robbers to investigate people’s reaction to acrime, and researchers may manipulate the number of other bystanders (confederates)present to determine when people are most likely to help (Latané &Darley, 1970). Similarly, confederates have been used to cut into a waiting linein order to study those already in line (Milgram, Liberty, Toledo, & Wackenhut,1986). In one field experiment, people’s reactions to the intrusion were lessenedwhen confederates also waited in line but did not object to the line cutting. Ourdiscussion of experimental methods will continue in Chapter 6.INDIRECT (UNOBTRUSIVE) OBSERVATIONAL METHODS• An important advantage of indirect observational methods is that they arenonreactive.• Indirect, or unobtrusive, observations can be obtained by examiningphysical traces and archival records.STRETCHING EXERCISEIn this exercise we ask you to respond to thequestions that follow this brief description of anobservational study.Students in a research methods class did an observationalstudy to investigate whether students’ability to concentrate while studying was affectedby where they studied. Specifically, students wereobserved in two locations on campus, the libraryand a lounge in the student union. The researchmethods students made their observations whileappearing to be studying in the library or the lounge.They observed only students sitting alone in eachlocation who had study materials such as a textbookor a notebook open in front of them. Duringa 5-minute observation period, the observers recordedthe amount of time each student was studying,as indicated by either looking at the materials orwriting. The student observers expected to find thatstudents would be able to concentrate better in thelibrary than in the student union.Five student observers made observationsfor a total of 60 students in the library and 50 studentsin the student-union lounge from 9 to 11 P.M.on the same Monday evening. The mean time thatstudents in the library spent studying was 4.4 ofthe 5.0 minutes. The corresponding mean timefor students in the student union was 4.5 of the5.0 minutes. The research methods students weresurprised by two aspects of their findings. First,they were surprised to find that students studiedfor nearly 90% of the 5-minute study interval.They were even more surprised that, contrary totheir prediction, the study times did not differ forthe two locations.1 Identify what type of observational method thestudents used in their study, and explain whatcharacteristics of their study you used to make youridentification.2 How might the decision to use 5-minute observationperiods affect the observers’ ability to studyconcentration?3 Why would the time-sampling plan in a study of thistype be especially important? How could the timesamplingplan used in this study be improved toincrease external validity?4 Consider for the sake of this question thatstudents can concentrate better in the librarythan in the student-union lounge. How couldthe nature of the material that the students werestudying in the two locations have led to thefinding that there was no difference between theobserved concentration by students in the libraryand in the student union?