Contents

454 Glossarysimple main effect Effect of one independent variable at one level of a second independentvariable in a complex design.simple random sampling (random selection) Type of probability sampling in whicheach possible sample of a specified size in the population has an equal chance ofbeing selected.single-factor independent groups design An experiment that involves independentgroups with one independent variable.single-subject experiment A procedure that focuses on behavior change in one individualby systematically contrasting conditions within that individual while continuouslymonitoring behavior.situation sampling Random or systematic selection of situations in which observationsare made with the goal of representativeness across circumstances, locations,and conditions.small-n research See single-subject experiment.social desirability Pressures on survey respondents to answer as they think theyshould respond in accordance with what is most socially acceptable, and not in accordancewith what they actually believe.spurious relationship What exists when evidence falsely indicates that two or morevariables are associated.stages of data analysis Three stages of data analysis are getting to know the data, summarizingthe data, and confirming what the data reveal.standard deviation The most commonly used measure of dispersion that indicatesapproximately how far on the average scores differ from the mean.standard error of the mean The standard deviation of the sampling distribution ofmeans.statistically significant When the probability of an obtained difference in an experimentis smaller than would be expected if error variation alone were assumed to beresponsible for the difference, the difference is statistically significant.stem-and-leaf display A technique for visualizing both the general features of a dataset and specific item information by creating leading digits as “stems” and trailingdigits as “leaves.”stratified random sampling Type of probability sampling in which the population isdivided into subpopulations called strata and random samples are drawn from eachof these strata.structured observation Variety of observational methods using intervention in whichthe degree of control is often less than in field experiments; frequently used by clinicaland developmental psychologists when making behavioral assessments.subject attrition A threat to internal validity occurs when participants are lost froman experiment, for example, when participants drop out of the research project. Theloss of participants changes the nature of a group from that established prior to theintroduction of the treatment—for example, by destroying the equivalence of groupsthat had been established through random assignment.successive independent samples design Survey research design in which a series ofcross- sectional surveys is done and the same questions are asked of each succeedingsample of respondents.summarizing the data In this second stage of data analysis the researcher uses descriptivestatistics and graphical displays to summarize the information in a data set.Trends and patterns in the data set are described.testing Taking a test generally has an effect on subsequent testing. Testing can threateninternal validity if the effect of a treatment cannot be separated from the effect oftesting.