Chapter 2 Glossary

constructa mental state that can’t be directly observed or manipulated, such as love, intelligence, hunger, feeling warm, and aggression (p. 49).

construct validity: the degree to which the study actually measures and manipulates the factors that the researcher claims to be measuring and manipulating. If the operational definitions of the constructs are poor, the study will not have good construct validity. For example, a test claiming to measure “aggressiveness” would not have construct validity if it really measured assertiveness. In some studies, the problem with construct validity is due to the participant guessing the hypothesis and then trying to give the researcher results that will support that hypothesis. (p. 51)



external validitythe degree to which the results of the study can be generalized to other places, people, or times. Sometimes, researchers repeat studies in a different setting (the real world rather than a lab), with a different participant population (people rather than rats), or at a different time, to test the external validity of a finding. In surveys, researchers may try to improve external validity by taking a random sample of their population (p. 55)



random samplingmaking sure that every person in the population has an equal chance of being selected to be in the study. It is very difficult to make sure that every person in the population has the same exact same chance of being in the study. Note that random sampling is very different from--and in many ways is the opposite of-- arbitrarily, haphazardly, accidentally, or unsystematically sampling. If you can get a list of your population, you could randomly sample from that population using this tool. Random sampling can help the external validity of your study (p. 56)

internal validity: the degree to which the study demonstrates that a particular factor caused a change in behavior. If a study lacks internal validity, the researcher may falsely believe that a factor causes an effect when it really doesn’t. Most studies involving humans do not have internal validity because they can’t rule out the possibility that some other factor may have been responsible for the effect. Unfortunately, steps taken to increase internal validity (such as keeping nontreatment factors constant) could harm the study’s external validity. (p. 41)


random assignmentusing a random process (similar to flipping a coin) to determine which of your participants will get which treatment. Thus, with random assignment, there is always some experimental manipulation--and not all participants will get the same manipulation. Random assignment is the backbone of  most psychological experiments because random assignment is one of the few ways a researcher can establish that a treatment caused an effect. In other words, random assignment helps establish internal validity.  (p. 45)


experiment:  a special type of study (not at studies are experiments!) that allows researchers to determine the cause of an effect; usually involves randomly assigning participants to groups. (p. 48)

ethical: conforming to a profession’s principles of what is morally correct behavior. In the case of psychological research, the American Psychological Association has established guidelines and standards of morally appropriate behavior. Usually, ethical human research must be approved by the school's Institutional Review Board (IRB) and involve both informed consent and debriefing. To learn more about these guidelines and standards, see Table 2-2, Table 2-3, Table 2-4, and Appendix C. (p. 56)

informed consent: Giving potential participants information about the study, especially in terms of factors that might lead them to refuse to be in the study, before they decide whether to participate. (p. 58)

debrief, debriefing: Explaining the purpose of the study, answering any questions, and undoing any harm that the participant may have experienced as a result of participating in the study. (p. 59)

Institutional Review Board (IRB): a committee of at least five members--one of whom must be a nonscientist--that review proposed research and monitor approved research in an effort to protect human research participants. To see a diagram of the IRB process, see Figure 2-7 (p. 63). For animal subjects, the equivalent committee is the Internal Animal Care and Use Committee (IACUC). (p. 61)


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