Solution Manual for Essentials of Statistics for the Behavioral Sciences , 2nd Edition

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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 population ofinterest, which we hope shares the same characteristics as thepopulation 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 is usedfor observations that have rankings (i.e., 1st, 2nd, 3rd . . .) as theirvalues. An interval variable has numbers as its values; the distance(or interval) between pairs of consecutive numbers is assumed tobe equal. Finally, a ratio variable meets the criteria for intervalvariables but also has a meaningful zero point. Interval and ratiovariables are both often referred to as scale variables.1.4Statisticians usescaleas another term for an interval or ratiomeasure. They also use scale as 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 either manipulateor observe to determine its effects on the dependent variable; adependent variable is the outcome variable that we hypothesizeto be related to, or caused by, changes in the independentvariable.1.7A confounding variable (also called a confound) is any variablethat systematically varies with the independent variable so thatwe cannot logically determine which variable affects thedependent 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 must bereliable, but a reliable measure is not necessarily a valid one.1.9An operational definition specifies the operations or proceduresused to measure or manipulate an independent or dependentvariable.1.10In everyday language, people often use the wordexperimenttorefer to something they are trying out to see what will happen.Researchers use the term to refer to a type of study in whichparticipants are randomly assigned to levels of the independentvariable.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 participants in the studyexperience all levels of the independent variable.1.13a.“This was an experiment” (not “This was a correlationalstudy”)b.“. . . the independent variable of caffeine . . .” (not “. . . thedependent 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 “. . . the ordinalvariable ‘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 . . .”)1.15The sample is the 100 customers who completed the survey.The population is all of the customers at the grocery store.1.16a.130 peopleb.All people living in urban areas in the United Statesc.Descriptive statisticAPPENDIXCSolutions to End-of-Chapter Problems

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