Statistics for the Behavioral Sciences Third Edition Solution Manual

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C-1C H A P T E R11.1Descriptive statistics organize, summarize, and communicate agroup of numerical observations. Inferential statistics use sampledata to make general estimates about the larger population.1.2A sample is a set of observations drawn from the populationof interest that, it is hoped, shares the same characteristics asthe population of interest. A population includes all possibleobservations about which we’d like to know something.1.3The four types of variables are nominal, ordinal, interval, andratio. A nominal variable is used for observations that havecategories, or names, as their values. An ordinal variable isused for observations that have rankings (i.e., 1st, 2nd, 3rd) astheir values. An interval variable has numbers as its values; thedistance (or interval) between pairs of consecutive numbers isassumed to be equal. Finally, a ratio variable meets the criteriafor interval variables but also has a meaningful zero point.Interval and ratio variables are both often referred to as scalevariables.1.4Statisticians usescaleas another term for an interval or ratiomeasure. They also usescaleas a word for many measurementtools, particularly those that involve a series of items that test-takers must complete.1.5Discrete variables can only be represented by specific numbers,usually whole numbers; continuous variables can take on anyvalues, including those with great decimal precision (e.g., 1.597).1.6An independent variable is a variable that we eithermanipulate or observe to determine its effects on thedependent variable; a dependent variable is the outcomevariable that we hypothesize to be related to, or caused by,changes in the independent variable.1.7A confounding variable (also called a confound) is any variablethat systematically varies with the independent variable sothat we cannot logically determine which variable affectsthe dependent variable. Researchers attempt to controlconfounding variables in experiments by randomly assigningparticipants to conditions. The hope with random assignment isthat the confounding variable will be spread equally across thedifferent conditions of the study, thus neutralizing its effects.1.8Reliability refers to the consistency of a measure.Validity refersto the extent to which a test actually measures what it wasintended to measure. A measure that is valid absolutely mustbe reliable, but a reliable measure is not necessarily a valid one.1.9An operational definition specifies the operations orprocedures used to measure or manipulate an independent ordependent variable.1.10In everyday language, people often use the wordexperimentto refer to something they are trying out to see what willhappen. Researchers use the term to refer to a type of studyin which participants are randomly assigned to levels of theindependent variable.1.11When conducting experiments, the researcher randomly assignsparticipants to conditions or levels of the independent variable.When random assignment is not possible, such as whenstudying something like gender or marital status, correlationalresearch is used. Correlational research allows us to examinehow variables are related to each other; experimental researchallows us to make assertions about how an independentvariable causes an effect in a dependent variable.1.12In a between-groups research design, participants experienceone, and only one, level of the independent variable. In awithin-groups research design, all levels of the independentvariable are experienced by all participants in the study.1.13a.“This was an experiment.” (not “This was a correlationalstudy.”)b.“. . . the independent variable of caffeine . . .” (not “ . . .the dependent variable of caffeine . . . ”)c.“A university assessed the validity . . .” (not “A universityassessed the reliability . . . ”)d.“In a between-groups experiment . . .” (not “In a within-groups experiment . . . ”)1.14a.“. . . the nominal variable ‘gender’ . . .” (not “. . . theordinal variable ‘gender’ . . .”)b.“A psychologist used a within-groups design . . .” (not “Apsychologist used a between-groups design . . .”)c.“. . . the effects of the independent variable . . .” (not “. . .the effects of the confounding variable . . .”)d.“A researcher studied a sample of 20 rats . . .” (not “Aresearcher studied a population of 20 rats . . .”)1.15a.An outlier is a participant or observation that is verydifferent from other observations in the study.b.When identifying why a particular observation is sodifferent from the other observations in the study (i.e.,outlier analysis), the researcher may gain insight into otherfactors that influence the dependent variable.Solutions to End-of-Chapter ProblemsappendixcNolan3e_interior_Appendix_C_Ch01.indd111/04/146:53 PM

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