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the time to respond, and take the time to mail their answers. Exactly who are you left with in the sample,
and what do the results mean? These are important questions to ask yourself as a consumer.

Case Analysis

On April 20, 1999, Eric Harris and Dylan Klebold entered Columbine High School and began shooting
teachers and students. Thirteen individuals died, and the psychological community was again asked to
explain such violent behavior. A psychologist might decide to interview Columbine students to obtain

their perspectives on the factors that motivated the two young men to commit such a horrendous act. A
group of ten students has already decided to meet and discuss the events of that day. The psychologist

asks if it would be all right to attend the meeting and ask them some questions. The students agree, and
the psychologist records their thoughts. Based on this information, the psychologist concludes that a
primary reason for the violent behavior was the peer dynamics in the school that created groups of

outcasts.

Critical Thinking Questions

1. Who appears to constitute the population of interest?
2. Which type of sampling procedure best describes that used by the psychologist?
3. What are the limitations of this sampling method, and in what specific ways could the sampling

method have affected the findings?
4. What specific steps would you have taken to obtain a representative sample?

General Summary

When we conduct research, we are generally interested in drawing some conclusion about a population of
individuals that have some common characteristic. However, populations are typically too large to allow

observations on all individuals, and we resort to selecting a sample. In order to make inferences about the
population, the sample must be representative. Thus, the manner in which the sample is drawn is critical.
Probability sampling uses random sampling in which each element in the population (or a subgroup of the

population with stratified random sampling) has an equal chance of being selected for the sample. This
technique is considered to be the best means of obtaining a representative sample. When probability

sampling is not possible, nonprobability sampling must be used. Convenience sampling involves using
participants who are readily available (such as introductory psychology students). It is the easiest
technique but the poorest from a methodological standpoint. Quota sampling is essentially convenience

sampling in which there is an effort to better represent the population by sampling a certain percentage of
participants from subgroups that correspond to the prevalence of those subgroups in the population.