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350 PART V: Analyzing and Reporting ResearchILLUSTRATION: DATA ANALYSIS FOR AN EXPERIMENTCOMPARING MEANSHow many words do you know? That is, what is the size of your vocabulary?You may have asked yourself this question as you prepared for collegeentrance exams such as the SAT or ACT, or perhaps it crossed your mind asyou thought about preparing for professional school exams such as the LSATor GRE, as all of these exams emphasize vocabulary knowledge. Surprisingly,estimating a person’s vocabulary size is a complex task (e.g., Anglin, 1993; Miller& Wakefield, 1993). Problems immediately arise, for instance, when we beginto think about what we mean by a “word.” Is “play, played, playing” one wordor three? Are we interested in highly technical or scientific words, includingsix-syllable names of chemical compounds? What about made-up words, orthe name of your dog, or the word you use to call your significant other? Onerather straightforward approach is to ask how many words a person knowsin a dictionary of the English language. But even here we run into difficultiesbecause dictionaries vary in size and scope, and thus results will vary dependingon the specific dictionary that was used to select a word sample. And,of course, estimates of vocabulary knowledge will vary depending on howknowledge is tested. Multiple-choice tests will reveal more knowledge thanwill tests requiring written definitions of words.One of the authors of your textbook was interested in the question of vocabularysize and conducted a study examining the vocabulary size of college studentsand older adults (see Zechmeister, Chronis, Cull, D’Anna, & Healy, 1995). Astratified (by letter of the alphabet) random sample of 191 words was selectedfrom a modest-sized dictionary of the English language. Then a multiple-choicetest with five alternatives was prepared. The correct meaning of the word appearedalong with four lures or distractors chosen to make discrimination of thecorrect meaning difficult. For example, respondents were asked to identify themeaning of the word “chivalry” among the following alternatives: a. warfare,b. herb, c. bravery, d. lewdness, e. courtesy. The random sample of dictionarywords was presented in booklets to 26 college-age students (mean age 18.5) and26 older adults (mean age 76). On the basis of previous studies, the older adultgroup was expected to perform better than the younger group on the test ofvocabulary knowledge.We’ll use data from this study of vocabulary size to illustrate the three stagesof data analysis.Stage 1: Getting to Know the Data• We begin data analysis by examining the general features of the data andedit or “clean” the data as necessary.• It is important to check carefully for errors such as missing or impossiblevalues (e.g., numbers outside the range of a given scale), as well as outliers.• A stem-and-leaf display is particularly useful for visualizing the generalfea tures of a data set and for detecting outliers.• Data can be effectively summarized numerically, pictorially, or verbally;good descriptions of data frequently use all three modes.