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Glossary 453reliability A measurement is reliable when it is consistent.repeated measures designs Research designs in which each subject participates in allconditions of the experiment (i.e., measurement is repeated on the same subject).repeated measures (within-subjects) t-test An inferential test for comparing twomeans from the same group of subjects or from two groups of subjects “matched” onsome measure related to the dependent variable.replication Repeating the exact procedures used in an experiment to determinewhether the same results are obtained.representativeness A sample is representative to the extent that it has the samedistribution of characteristics as the population from which it was selected;our ability to generalize from sample to population is critically dependent onrepresentativeness.response rate bias Threat to the representativeness of a sample that occurs when someparticipants selected to respond to a survey systematically fail to complete the survey(e.g., due to failure to complete a lengthy questionnaire or to comply with a requestto participate in a phone survey).reversal design See ABAB design.risk/benefit ratio Subjective evaluation of the risk to a research participant relativeto the benefit both to the individual and to society of the results of the proposedresearch.sample Something less than all the cases of interest; in survey research, a subset of thepopulation actually drawn from the sampling frame.scatterplot A graph showing the relationship between two variables by indicating theintersection of two measures obtained from the same person, thing, or event.scientific method Approach to knowledge that emphasizes empirical rather thanintuitive processes, testable hypotheses, systematic and controlled observation ofoperationally defined phenomena, data collection using accurate and precise instrumentation,valid and reliable measures, and objective reporting of results; scientiststend to be critical and, most important, skeptical.selection Selection is a threat to internal validity when, from the outset of a study,differences exist between the kinds of individuals in one group and those in anothergroup in the experiment.selection bias Threat to the representativeness of a sample that occurs when theprocedures used to select a sample result in the over- or underrepresentation of asignificant segment of the population.selective deposit Bias that results from the way physical traces are laid down and theway archival sources are produced, edited, or altered, as they are established; whenpresent, the bias severely limits generality of research findings.selective subject loss Occurs when subjects are lost differentially across the conditionsof the experiment as the result of some characteristic of each subject that is related tothe outcome of the study.selective survival Bias that results from the way physical traces and archives sur viveover time; when present, the bias severely limits the external validity of researchfindings.sensitivity Refers to the likelihood in an experiment that the effect of an independentvariable will be detected when that variable does, indeed, have an effect; sensitivityis increased to the extent that error variation is reduced (e.g., by holding variablesconstant rather than balancing them).simple interrupted time-series design Quasi- experimental procedure in whichchanges in a dependent variable are observed for some period of time both beforeand after a treatment is introduced.