Contents

366 PART V: Analyzing and Reporting Researchscores provided by each subject. The mean of the difference scores (“D bar”)is defined as__D DNwhere D a difference score and N is the number of difference scores (i.e.,number of pairs of scores). Note that __ D __ X 1 __ X 2 .The estimated standard error of the difference scores ( s __ D ) is defined as__s D s D____ Nwhere s Dis the standard deviation of difference scoresCritical values of t are obtained by consulting Appendix Table A.2 with degreesof freedom equal to N 1. Note that in this case N refers to the number of participantsor pairs of scores in the experiment.The confidence interval for the difference between two means in a repeatedmeasures design can be defined asCI __ D ( t 0.5 )( s __ D )Confidence Intervals for a Comparison Among Several Independent Group MeansTo illustrate the use of confidence intervals to analyze and interpret resultswhen there are more than two means, we consider a study on how infants“grasp the nature of pictures” (DeLoache, Pierroutsakos, Uttal, Rosengren, &Gottlieb, 1998). Have you ever wondered whether infants understand that apicture of an object is not the same thing as the object itself? DeLoache and hercolleagues were intrigued by research demonstrating that infants as young as5 months seem to recognize the similarity between objects and their pictures,but also seem to recognize they’re not the same. However, these research findingsdo not correspond well to anecdotes of infants’ behavior toward picturesin which infants and young children try to grasp or pick up the objects representedin pictures, and even try to step into a picture of a shoe! These anecdotalreports suggest that infants and children treat pictured objects as if they arereal objects, despite the two-dimensional representation in the picture. In fourstudies, DeLoache et al. examined “to what extent infants would treat depictedobjects as if they were real objects” (p. 205).We will focus on the results of the fourth study carried out by DeLoache et al.(1998). In the first three studies the researchers found that• a large majority of 9-month-old infants, when exploring a picture book with“eight highly realistic color photographs of individual objects (commonplastic toys),” tried to grasp a pictured object at least once (the average was3.7 attempts) (Study 1);• infants’ grasping at pictures was not because the infants could notdiscriminate between two- and three-dimensional objects (Study 2); and• “Beng infants from severely impoverished and largely nonliterate familiesliving in a rural village in the West African nation of Côte d’Ivoire (Ivory