Consider five high school students working on homework in study hall. 
Which of the following pairs of students has a double coincidence of wants?
Definitions:
Controlled Observations
Observational research methods where variables are manipulated or controlled in order to investigate their effects on other variables.
Naturalistic Observations
A research method in which subjects are observed in their natural environment without any manipulation by the researcher.
Introspection
The study or monitoring of one's own thoughts and feelings.
Ecological Validity
The extent to which the findings of a study can be applied to and represent real-world settings and behaviors outside the context of the study itself.
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