Contents

160 PART II: Descriptive Methodssample. These findings suggest that decreases in eating-disorder attitudes andbehaviors may reflect changes at a societal level over the 10-year period (e.g.,due to increasing information about eating disorders in the media). One potentialproblem with longitudinal survey designs is that it is difficult to pinpointthe exact causes for individuals’ changes over time. 1What can be said about eating attitudes and behaviors 20 years following college?Overall, women demonstrated more weight dissatisfaction, dieting, andeating-disorder attitudes than men across the 20 years of the survey (Keel et al.,2007). In the 2002 survey, researchers observed that, on average, body weightincreased significantly for both men (17 pounds since college) and women(14 pounds since college). Men’s dieting and weight dissatisfaction was greatestin 2002, paralleling their weight gain. Interestingly, by the time the womenin the study were in their early forties, despite their weight gain, they reportedless dieting, less disordered eating, and less dissatisfaction with their body. Infact, women’s greatest dissatisfaction with their body occurred while in college.Based on their statistical analyses, Keel et al. suggested that adult roles attainedthrough marriage, parenthood, and careers were associated with decreases inwomen’s disordered eating. That is, while physical appearance was importantduring college years (e.g., for attracting a potential mate), changes in prioritiesassociated with marriage and becoming a mother made women’s desire forthinness less important.Another potential problem with longitudinal designs is that it can be difficultto obtain a sample of respondents who will agree to participate over timein a longitudinal study. In addition, you might think the longitudinal designsolves the problem of noncomparable samples because the same people participateover and over (so of course the sample represents the same populationeach time). Unfortunately, the samples over time in a longitudinal designare identical only if all members of the original sample participate throughoutthe study. This is unlikely. For example, in the Heatherton et al. (1997) study,of the 901 participants in the original 1982 sample, only 724 (80%) returneda usable survey in 1992. In the third panel in 2002, 654 (73%) of the original900 participants from 1982 responded to the survey and of these, 561 (86%) alsoresponded to the 1992 survey. Thus, by the end of the 20 years, the researchershad survey responses for each of the three time periods (1982, 1992, 2002) for62.3% of their original sample of 900 respondents.Unless all the respondents in the original sample complete all phases of alongitudinal design, there is a possible problem due to attrition. Attrition is probablythe most serious disadvantage of the longitudinal design because as samplesdecrease over time, they are less likely to represent the original populationfrom which the sample was drawn. It is usually possible, however, to determinewhether the final sample is comparable to the original sample in a longitudinaldesign. The characteristics of nonrespondents in the follow-up phase(s) areknown because they participated in the original sample. Therefore, researchers1Heatherton et al. (1997) noted that because the decreases in problem eating were larger amongindividuals in the longitudinal survey than in the successive independent samples survey, maturationalprocesses within individuals, in addition to societal changes, likely were operating todecrease problem eating over time.