Construct Validity of Physical Self-Description Questionnaire Responses: Relations to External Criteria

Transcription

1 JOURNAL OF SPORT &EXERCISE PSYCHOLOGY, 1996,18, O 1996 Human Kinetics Publishers. Inc. Construct Validity of Physical Self-Description Questionnaire Responses: Relations to External Criteria Herbert W. Marsh University of Western Sydney, Macarthur The Physical Self-Description Questionnaire (PSDQ) is a multidimensional physical self-concept instrument with 11 scales: Strength, Body Fat, Activity, EnduranceFitness, Sports Competence, Coordination, Health, Appearance, Flexibility, Global Physical, and Global Esteem. The purpose of this study is to evaluate the construct validity of PSDQ responses in relation to 23 external criteria, including measures of body composition, physical activity, endurance, strength, and flexibility for 192 (113 boys and 79 girls) high school students. Each external validity criterion was predicted a priori to be most highly correlated with one of the PSDQ scales. In support of the convergent validity of the PSDQ responses, every predicted correlation was statistically significant. In support of the discriminant validity of the PSDQ responses, most predicted correlations were larger than other correlations involving the same criterion. These results support the construct validity of PSDQ responses in relation to external criteria and their potential usefulness in a wide variety of sports and exercise settings. Key words: physical self-concept, physical fitness, convergent validity, discirninent validity Construct validation is an ongoing process in which theory and practice are used to develop an instrument, empirical research is used to test the theory and interpretations of responses from the instrument, both the theory and the instrument are revised in relation to research, and theory and research are used to inform practice (Marsh, in press; Marsh, Richards, Johnson, Roche, & Tremayne, 1994; Nelson, 1989; Ostrow, 1990; Vealey, 1986). For example, Gill, Dzewaltowski, and Deeter (1988) argued for the construction of multidimensional sport and exercise instruments based on theory, followed by item and reliability analysis, exploratory and confirmatory factor analysis, tests of convergent and divergent validity, and application in research and practice. However, Ostrow (1990) laments that despite substantial gains over the last 25 years, many sport psychology instruments are still "one shot assessments," lacking further development and refinement. Herbert W. Marsh is with the University of Western Sydney, Macarthur, P.O. Box 555, Campbelltown, NSW 2560.

2 112 / Marsh Construct validity investigations can be classified as within-network (internal or structural) studies and between-network (external) studies (Marsh, in press; Shavelson, Hubner, & Stanton, 1976; also see Messick, 1989). Within-network studies explore the internal structure of self-concept. They test, for example, the dimensionality of self-concept and may seek to show that the construct has consistent, distinct multidimensional components (e.g., physical, social, academic self-concept) or that a specific domain like physical self-concept has multiple dimensions (e.g., strength, endurance, appearance, sports competence). Within-network studies typically employ empirical techniques such as factor analysis or multitrait-multimethod (MTMM) analysis. Between-network studies attempt to establish a logical, theoretically consistent pattern of relations between measures of self-concept and other constructs. The resolution of at least some within-construct issues should be a logical prerequisite to conducting between-construct research. Marsh (in press) briefly reviewed the status of physical self-concept measurement. Historically, research in this area stemmed primarily from research into body image and its relation to global esteem. More recently there has been a greater emphasis on multidimensional self-concept instruments that typically contain one or more physical scales that can be differentiated from other specific domains of self-concept and general self-concept. However, such scales may combine and confound apparently distinguishable physical components such as health, body composition, physical attractiveness, physical fitness, and strength (Fox & Corbin, 1989; Marsh & Richards, 1988). Inevitably, such concerns led to the development of multidimensional physical self-concept scales such as the Physical Self-Description Questionnaire (PSDQ; Marsh, in press; Marsh et al., 1994). The PSDQ is designed to measure nine specific components of physical self-concept (Strength, Body Fat, Activity, Endurancemitness, Sports Competence, Coordination, Health, Appearance, Flexibility), Global Physical Self-concept, and Global Esteem. The theoretical rationale for the PSDQ is based on the Marsh/ Shavelson self-concept model and previous Self-Description Questionnaire (SDQ) research. The PSDQ scales reflect some scales from the SDQ instruments (Physical Ability, Physical Appearance, and Self-Esteem), scales from the earlier version of the PSDQ presented by Marsh and Redmayne (1994), and an attempt to parallel components of physical fitness identified in Marsh's (1993b) confirmatory factor analyses of physical fitness indicators from the Australian Health and Fitness Survey based on Fleishman's (1964) structure of physical fitness. Each of the 11 scales is intended to measure a stable, relatively independent physical self-concept trait. However, consistent with the Marsh/Shavelson model, there is a hierarchical ordering in which general self-concept is at the apex, global physical self-concept is at the next level, and the specific components of physical self-concept are at the third level. Although all PSDQ components contribute to general self-concept in a hierarchical factor analysis, the PSDQ Global Esteem scale should be most strongly related to this highest order factor. Similarly, although each of the PSDQ components is predicted to contribute to the Global Physical factor, the PSDQ Global Physical scale is predicted to contribute most (see Marsh, 1993a, in press; Marsh & Redmayne, 1994). Thus far, PSDQ research has focused on the within-network concerns, emphasizing tests of the hypothesized factor structure underlying PSDQ responses. Marsh et al. (1994) supported the a priori PSDQ factor structure in two samples of high school students and the replicability of the PSDQ factor structure in responses

3 Psysical Self-Description Questionnaire / 1 13 by men and women. In a MTMM study of relations between PSDQ responses and responses to two other physical self-concept instruments, Marsh et al. (1994) also found support for the convergent and discriminant validity of PSDQ responses. Marsh and Roche (in press-a) demonstrated support for the stability of PSDQ responses over time and further support for their discriminant validity in an application of MTMM analyses to longitudinal data. Marsh (1993~) related single-item measures of physical and academic self-concept to 14 field and laboratory indicators of physical fitness and to academic achievement for a large (N = 6,283), national representative sample of Australian students aged 9-15 years. Correlations between self-concepts and the corresponding external criteria increased steadily with age in both the physical and academic domains. Although girls had slightly lower physical fitness self-concepts, correlations with objective indicators were similar for boys and girls. Consistent with predictions from Marsh's frame of reference model, relations were stronger after controlling for gender and particularly age, suggesting that self-concepts are formed relative to other students of a similar age and gender. Thus, for example, performances by a young girl may be poorer in absolute terms than those of older girls and of boys, but may still be good relative to those of other girls who are in the same year in school, thus leading to a positive physical self-concept. Although the directions of relations were consistent with a priori predictions for all 14 fitness indicators, the global measure of physical-concept was more strongly related to some components of fitness (e.g., cardiovascular endurance, power, dynamic strength, and body composition) than others. Consistent with multidimensional perspectives of physical fitness, indicators from a variety of fitness domains contributed to fitness self-concepts. However, because the database contained only a single-item measure of physical self-concept, it was not possible to test the construct validity of multiple dimensions of physical self-concept, like those measured by the PSDQ. The confirmatory factor analysis and MTMM studies based on PSDQ responses (Marsh, in press; Marsh et al., 1994) provide good support for the construct validity of PSDQ responses in relation to within-network concerns. However, there is an important need to evaluate PSDQ responses in relation to external validity criteria, a between-network concern. More generally, Marsh (in press) noted that none of the multidimensional physical self-concept instruments have been evaluated in relation to an extensive set of external criteria such as objective measures of body composition, physical activity levels, and physical fitness measures designed to measure different components of physical fitness. Hence, the purpose of the present investigation is to pursue such between-network studies of the construct validity of PSDQ responses. Measures Methods Physical Self-Description Questionnaire (PSDQ). The PSDQ is a 70-item test designed to measure nine specific components of physical self-concept and two global components that can be characterized as follows. The two coefficients in parentheses are coefficient alpha estimates of reliability and 3 month test-retest stability coefficients, respectively, presented by Marsh and Roche (in press-a):

4 114 / Marsh Appearance: Being good looking, having a nice face (.91,.78) Strength: Being strong, having a powerful body with lots of muscles (.92,.89) Endurance: Being able to run a long way without stopping, not tiring easily when exercising hard (.92, 37) Flexibility: Being able to bend and turn your body easily in different directions (.90, 33) Health: Not getting sick often, getting well quickly when you are sick (27,.70) Coordination: Being good at coordinated movements, being able to do physical movements smoothly (.91, 33) Activity: Being physically active, doing lots of physical activities regularly (.90, 32) Body Fat: Not being overweight, not being too fat (.96,.89) Sport: Being good at sports, being athletic, having good sports skills (.94,.87) Global Physical: Feeling positive about one's physical self (.96, 32) Esteem: Overall positive feelings about self (.91, 39) The theoretical basis, design, and initial research with the PSDQ (see earlier discussion) are based substantially on the SDQ instruments that are widely acknowledged to be among the strongest of multidimensional self-concept instruments (see reviews by Boyle, 1994; Hattie, 1992; Wylie, 1989; also see Marsh, 1990, 1993a). Each PSDQ item is a simple declarative statement and participants respond using a 6-point true-false response scale. The instructions, response format, and layout of the instrument are based on the wisely used SDQII instrument (Marsh, 1992). Marsh (in press; Marsh et al., 1994) summarized support for the reliability of the PSDQ scales, confirmatory factor analysis tests of the structure underlying PSDQ responses and its invariance over gender, convergent and discriminant validity based on a MTMM analysis of responses to three physical self-concept instruments, and convergent and discriminant validity based on responses to the PSDQ collected on four occasions by the same respondents. The PSDQ has been used with participants between 12 and 18 years of age, but should be appropriate for older participants as well. External Validity Criteria. The external validity criteria used in the present investigation were based in part on the measures included in the Australian Health and Fitness Survey and were administered according to protocols used in that research (Pyke, 1987). Some external validity criteria (silhouette ratings, self-report physical activity measures) were collected as part of a survey that also contained the PSDQ. The remaining external validity criteria were part of a physical fitness battery collected as part of the normal physical education classes. The following provide descriptions of the external criteria and the PSDQ scale each is predicted to be most highly correlated. Body Composition. Body composition was determined using the following: Body mass index: WeightJheight2 with weight measured in kilograms and height measured in meters. This is predicted to be most highly correlated to PSDQ Body Fat. Body girth (in centimeters assessed using a constant tension tape): The mean girth measured at three sites: mid-arm girth, waist girth, and hip girth. This is predicted to be most highly correlated to PSDQ Body Fat.

5 Psysical Self-Description Questionnaire Skinfolds (in millimeters measured with a Holtain caliper): The mean skinfold measured at seven sites: triceps, biceps, subscapular, superailiac, abdominal, front thigh, and medial calf. This is predicted to be most highly correlated to PSDQ Body Fat. Body composite: The mean of the BMI, body girth, and skinfold measure after each score was standardized to have mean = 0, SD = 1 (i.e., a z-score transformation). This is predicted to be most highly correlated to PSDQ Body Fat. Silhouette Ratings. Students were presented with a set of 9 male silhouettes and 9 female silhouettes varying from very skinny to very obese and asked to answer different questions in relation to the silhouettes (Marsh & Roche, in press-b): Actual rating: "What do you look like today?' This is predicted to be most highly correlated to PSDQ Body Fat. Actual-ideal discrepancy: The difference between the actual rating and responses to the item, "If you were completely free to choose, how would you ideally like to look?"is is predicted to be most highly correlated to PSDQ Body Fat. Physical Activity ParticipatiodAdherence. Students were asked to think about the possibility of starting or continuing a program of regular physical activity doing something like gym, sport, jogging, aerobics, or exercise hard enough to make them huff and puff for at least 30 minutes and doing this at least three times a week. Using a 6-point true-false scale, students were then asked to respond to the following statements: Past participation: "I have done a physical activitylexercise program like this in the past." This is predicted to be most highly correlated to PSDQ Physical Activity. Present participation: "I am currently doing a physical activitylexercise program like this." This is predicted to be most highly correlated to PSDQ Physical Activity. Future desired participation: "I would like to do (or continue) a physical activitylexercise program like this in the near future." This is predicted to be most highly correlated to PSDQ Physical Activity. Future intended participation: "I actually intend to do (or continue) a physical activitylexercise program like this in the near future." This is predicted to be most highly correlated to PSDQ Physical Activity. Benefits: "I would want to do a program like this because [followed by 14 potential benefits such as health, weight control, fun, make friends, reduce stress, feel better about myself]." This is predicted to be most highly correlated to PSDQ Physical Activity. Barriers: "I would not want to do a program like this because [followed by 14 potential barriers such as would take too much time, would be boring, I am lazy, cost, health problems, don't have right clothes or equipment]." This is predicted to be most highly correlated (negatively) to PSDQ Physical Activity. Commitment: "If I began (or continued) a program I would do it even when [followed by 13 potential conflicts such as had other things to do, too much

6 116 / Marsh schoolwork, feeling tired, bad weather, felt embarrassed, felt depressed]." This is predicted to be most highly correlated to PSDQ Physical Activity. Physical Activity Levels. In a self-report survey, students were asked the following: Timeltypical week: "In most weeks how many times do you do a physical activity (e.g., walking fast, jogging, bicycling, sports, exercise, aerobics): none, once a week, twice a week, three times a week, etc." This is predicted to be most highly correlated to PSDQ Physical Activity. Hoursltypical week: Response to the item "How many times a week do you do regular physical activity or exercise in a typical week?'was multiplied by the response to the item "How many minutes do you typically exercise each time you exercise?'and was then divided by 60. This is predicted to be most highly correlated to PSDQ Physical Activity. Last 7 days: Students were asked to pick a typical weekday and weekend day during the last week and indicate the number of hours spent doing activity in each of five categories so that the total number of hours for each day was 24. For present purposes only hours in the following two categories were included: "very hard activity" (makes you huff and puff or sweat a lot, makes your heart beat fast; e.g., running hard, competitivelhard swimming, competition soccer, squash, running upstairs, bicycling hard, mountain climbing, carrying a load upstairs, chopping wood, competition netball, fast aerobics) and "hard activity" (makes you huff and puff or sweat a little; e.g., roller skating, fast disco dancing, basketball, walking fast uphill, cross-country hiking, jogging, swimming laps, tennis, climbing stairs or a ladder, aerobics, touch football, softball/baseball, moving heavy furniture). A weighted average was computed in which the number of hours spent in very heavy activity was weighted 2 and the number of hours spent in heavy activity was weighted 1. This is predicted to be most highly correlated to PSDQ Physical Activity. Endurance. Endurance was measured with the following tests: 1.6-km run: Time required to complete a 1.6-km course. This is predicted to be most highly correlated to PSDQ Endurance. Beep test: The "beep" test is a multistage progressive shuttle run test that can be used to predict maximum oxygen uptake (Leger & Lambert, 1982). In this test, students performed a shuttle-run in which they went back and forth over a 20-m distance in time with a prerecorded beep signal until they were unable to keep up with the signal. The time between beeps decreased such that the speed required to complete the 20-m shuttle increased by 0.5 km. hrl each minute. The maximum test duration is 21 minutes. This is predicted to be most highly correlated to PSDQ Endurance. Explosive/Dynamic Strength. Strength was determined using the following: Basketball throw: In the basketball throw, students sat with their back against a wall and legs out straight, held a basketball at chest level with arms tucked into the chest, and threw the ball as far as possible with a pushing motion. This is predicted to be most highly correlated to PSDQ Strength, although it also has a skill component that might be related to PSDQ Sport.

7 Psysical Self-Description Questionnaire / 1 17 Modified pull-up: In the modified pull-up, students used a bar that was not more than 1 m above the ground so that their heels were always touching the ground while they were pulling themselves up. The actual height of the bar was adjusted so that it was just out of reach when a student lay flat on histher back with arms stretched up towards the bar. This is predicted to be most highly correlated to PSDQ Strength, although it also has a skill component that might be related to PSDQ Sport. 50-m dash: Time (measured in seconds, with a hand-held stopwatch), after a warm-up, to complete a 50-m sprint over a straight track. This is predicted to be most highly correlated to PSDQ Strength, although it also has a skill component that might be related to PSDQ Sport. Standing long jump: The longest of two jumps (in centimeters) done from a standing takeoff. This is predicted to be most highly correlated to PSDQ Strength, although it also has a skill component that might be related to PSDQ Sport. Flexibility/Joint Mobility. Mobility was measured using a sit and reach. The students were seated with legs straight in front and asked to stretch as far as possible toward or beyond their toes and to hold that position for 3 seconds. The score is the centimeters beyond their toes (or negative scores if they do not reach their toes). This is predicted to be most highly correlated to PSDQ Flexibility. It is also important to note that correlations between the PSDQ Global Physical scale and the external validity criteria are expected to be substantial. This follows from the rationale of this scale as an indicator of global physical self-concept that incorporates each of the more specific PSDQ scales. Similarly, the PSDQ Sport Competency scale is expected to be substantially related to performance measures that have a substantial skill component (e.g., the strength indicators). Participants and Procedures Participants were 192 (113 boys and 79 girls) high school students in Years 7 (mostly 13 years of age) to Year 9 (mostly 15 years of age) from aprivate, comprehensive, coeducational high school in metropolitan Sydney, Australia. Students came from a wide range of family backgrounds, varying from lower middle class to upper middle class. All students in attendance on the day completed a battery of survey instruments as part of the baseline data from a larger study. Parental consent forms were sent by the school to all parents prior to the start of the study explaining the nature of the research, and only students who had parental permission to participate in the study were tested. Teachers from the high school were asked to complete the questionnaire themselves and then met with project staff for training on how to administer the survey instrument. The instrument was then administered by teachers to intact classes of no more than 30 students. The objective body composition measures and physical fitness measures were part of a physical fitness battery administered between 5 and 8 weeks later. These measures were administered by sports science students from the University of Western Sydney according to standard protocols as part of the normal physical education classes that are required of all students in Years 7 to 9. The university students were trained and supervised by the research project staff, were assessed on their ability to administer the tests, and received academic credit for their participation in the study as part of their field experience requirement.

8 118 / Marsh Statistical Analysis The set of 23 external validity criteria (including body composite, the sum of three other measures) were correlated with 11 PSDQ scales. Because the physical fitness battery had to be collected in 3 or 4 different class sessions during a 3-week period, not all students completed all of the measures in the battery. For purposes of this analysis, responses were included for all students (N = 192) who completed the self-report survey (containing the PSDQ, silhouette ratings, and physical activity measures) and a majority of the physical fitness measures (192 out of 201 students). The ns for the different external criterion measures varied from 192 to 179 (median n = 189; see subsequent discussion of Table 1 where the ns are presented). All correlations were computed using pairwise deletion for missing data. For each criterion, the PSDQ scale to which it should be most highly correlated was predicted a priori (see earlier discussion). An evaluation of the construct validity of the PSDQ responses follows the logic of MTMM analyses that distinguishes between convergent validity and discriminant validity. Using the traditional approach used to evaluate MTMM correlation matrices (Campbell & Fiske, 1959; Marsh, 1988; Marsh et al., 1994), (a) support for the convergent validity of the PSDQ responses requires that each predicted correlation is statistically significant, and (b) support for the discriminant validity of the PSDQ responses requires that each external validity criterion is more highly correlated with the predicted PSDQ scale than any of the other PSDQ scales. If all the convergent validities (i.e., the predicted correlations) are statistically significant, then there is support for convergent validity. If all the convergent validities are larger than other correlations involving the same external validity criterion, then there is support for discriminant validity as well. In this respect, the traditional approach to the assessment of convergent and discriminant validity is largely descriptive. Interpretations of the correlations are complicated by the effects of gender, year in school, and perhaps, body composition. As described earlier, consistent with predictions based on Marsh's (1993~) frame of reference model, relations between physical self-concept and external validity criteria-particularly performance measures that vary with gender and year in school-tended to be higher after controlling for the effects of gender, year in school, and their interaction. Here, year in school is used as a convenient indicator of age. However, for purposes of testing Marsh's (1993~) frame of reference model, year in school may be more appropriate than age in that students are likely to make comparisons with other students in their same year in school. Also, scores on some physical fitness measures may be more appropriately evaluated in relation to some measure of body composition. Thus, for example, the pull-up and standing long jump depend in part on body weight. In order to examine these issues, three sets of correlations were computed. Zero-order correlations between PSDQ responses and the external validity criteria did not control for any other variables (i.e., they are the typical product-moment correlation). The effects of gender, year-in-school, and the Gender x Year-in-School interaction were controlled in the first set of partial correlations, and the additional effects of the body composite measure were controlled (as well as the effects of gender and year-in-school) in the second set of partial correlations.

9 Table 1 Relations Between PSDQ Scales and External Validity Criteria: Zero-order Correlations (0) and Partial Correlations Controlling for Gender and Year in School (1) and for Body Composite (2) PSDQ Scales Varible N Partial Bfat Appr Pact Endur Strg Flex Coord Sport Heal Gpyhs Esteem Body composition Body mass index I ll OO I9 -.I OO I6 Girths I I I4 cc Skinfolds I I9 LA p I lo OO I I I Body composite I9 ;i; I7 Q 2.oo.oo -00,00.oo.oo.oo.oo.oo.oo.oo E' Silhouette ratings 9 Actual I I I I E..? (continued) w w \D

10 e Table 1 (continued) 8 'r 5 Varible N Partial Bfat Appr Pact Endur Strg Flex Coord Sport Heal Gpyhs Esteem 2 a Actual-Ideal Activity participatiodadlzerence Past particip Present particip Future desire Future intention Barriers Benefits Commitment

11 Activity levels Timesltypical wk Hoursltypical wk ll Hours last 7 days Endurance 1.6-krn run I Beep test g Dynarnic/explosive strength U Basketball throw ll $ , Modified pull-up in g tl (cotninued) g, CD -. +A h) C

12 Table 1 (continued) % a PDQ Scales 5 Varible N Partial Bfat Appr Pact Endur Strg Flex Coord Sport Heal Gpyhs Esteem 50-m Dash 182 Stand Long Jump 187 Flexbility Sit and Reach 182 Demographic Covariates Year in school 192 Gender 192 Y x G interaction 192 Note. N for each of the 11 PSDQ scales is 192 and Ns for other variables are presented. All correlations and partial corerlations were computed with pairwise deletion for missing data. Presented are zero-order correlations in which no variables are controlled (those with 0 under the column labeled partial); partial correlations in which the effects of gender, year in school, and the Gender x Year in school interaction are controlled (1); and partial correlations in which the effects of gender, year in school, the Gender x Year in School and the body composite (a composite of the three body composition measures-body mass index, girths, and skin folds) are controlled (2). (Correlations in italic are predicted a priori to be significant are the basis for evaluations of construct validity. All correlations greater than.15 are statistically <.05, two-tailed).

13 Psysical Self-Description Questionnaire Results Relations between PSDQ responses and a diverse range of external validity criteria are summarized in Table 1. For each external validity criterion, the PSDQ scale that should be most highly correlated with each criterion was predicted a priori (the italic coefficients in Table 1). To the extent that these correlations are meaningfully large and statistically significant, there is support for the convergent validity of the PSDQ responses. Typically, this is the aspect of construct validity that receives the most emphasis, but it is also important to evaluate the size of correlations between each external validity criterion and the other PSDQ scales. To the extent that these are smaller than the convergent validity coefficients, then there is also support for the discriminant validity of the PSDQ ratings. Body Composition Objective measures of body fat based on the body mass index (BMI), body girths, skinfolds, and their composite are substantially related to the PSDQ Body Fat scale (which is scored so that self-perceptions of being fat result in low scores). Partialing out the effects of year in school and gender has little effect on the sizes of these relations. Partialing out the effects of body composite, not surprisingly, eliminates relations between the PSDQ Body Fat scale and the individual components of the body composite measure (BMI, girths, skinfolds). Thus, there is no residual variance in any of the body composition measures (e.g., variance in the skinfold measure that cannot be explained by the body composite measure) that is significantly related to Body Fat self-concept. In the silhouette ratings, students were asked to pick one of nine silhouettes varying in body fat that best represented their actual body and their ideal body. Consistent with predictions, actual ratings and actual-ideal discrepancy scores are substantially related to the PSDQ Fat scale. Ideal body is not very highly correlated with any PSDQ scales, but the actual-ideal discrepancy is more highly correlated with PSDQ Body Fat than is the actual score alone. This is consistent with the notion that self-concept is affected by both (absolute) self-perceptions and the standards against which the self-perceptions are evaluated. Controlling for the effects of year in school and gender has little effect on these relations, but controlling for the body composite measure substantially reduces their size. It is, however, interesting to note that there is still a substantial relation between the silhouette ratings and the PSDQ Body Fat scale even after removing the effects of objective measures of body composition. Correlations drop from about.7 (about 50% of the variance explained) to about.5 (25% of the variance explained). Apparently, self-perceptions of body fat that are reflected in both the silhouette and Body Fat self-concept measures cannot be explained completely by the objective measures of body composition. The substantial relations between the PSDQ Body Fat responses and measures of body composition and the silhouette ratings support the convergent validity of the PSDQ responses. It is also important to emphasize that these external validity criteria are substantially less correlated with other PSDQ scales, supporting the discriminant validity of PSDQ responses. It is not surprising, of course, that body composite measures are significantly and negatively related to other

14 124 1 Marsh specific components of physical self-concept (e.g., Endurance, Sports Competence, Flexibility, Coordination, Physical Appearance) and the global physical scale. It is, however, surprising that these external validity criteria are not more substantially related to the PSDQ Physical Appearance scale and, perhaps, to Global Esteem. Although the explanation for this finding is beyond the scope of the present investigation, it provides strong support for the decision to represent Body Fat and Physical Appearance as separate scales on the PSDQ. Taken together, these results support the convergent and discriminant validity of the PSDQ responses. Physical Activity ParticipatiodAdherence and Activity Levels The set of four physical activity participationladherence ratings asks whether students have participated in a program of regular physical activity in the past, whether they are currently participating in such a program, whether they would like to do so in the future, and whether they actually intend to do so. Consistent with a priori predictions, all four of these measures are substantially correlated with the PSDQ Physical Activity scale and less correlated with other PSDQ scales. Within the set of four ratings, current participation is more highly correlated with the PSDQ scale, whereas past participation and future intentions are somewhat less highly correlated. Partialing out the effects of gender, year in school, and body composite has little effect on either the size or pattern of correlations. Students rated barriers to participation, benefits of participation, and the strength of their commitment to participation. Each of these measures is significantly related to the PSDQ Physical Activity scale and less highly correlated with the other PSDQ scales. However, it is interesting to note that barriers to participation is much more highly correlated to PSDQ Physical Activity than either commitment or benefits. Partialing out the effects of year in school, gender, and body composition has little effect. Students indicated the number of times per week they typically undertook physical activity, the amount of time they typically spent, and detailed ratings of activity levels during the last 7 days. All three measures are significantly related to the PSDQ Physical Activity measure, but surprisingly, the apparently crude "number of times" measure is more highly correlated with the PSDQ Physical Activity measure than either of the more detailed measures that incorporate the amount of time spent. This pattern of results may reflect inherent difficulties that students had in making time estimates and classifying activities into different levels of physical activity (see Marsh & Johnson, 1994). Although the number of times and amount of time typically spent are more highly correlated with the PSDQ Physical Activity scale than other PSDQ scales, the 24-hour ratings are more highly correlated with the PSDQ Sports Competence scale. The sizes of these relations are reduced marginally by controlling body composition, but the pattern of relations is largely unaffected. In summary, correlations between PSDQ responses and program participation, adherence, and physical activity levels support the convergent and discriminant validity of the PSDQ ratings. Physical Endurance As predicted, the two field indicators of physical endurance-the 1.6-km run and the beep test-are substantially related to the PSDQ Endurance scale and

15 Psysical Self-Description Questionnaire / 125 less correlated with other PSDQ scales. Also consistent with expectations, both measures are substantially related to the PSDQ Sports Competence scale and, to a lesser extent, the Global Physical scale. Consistent with predictions based on Marsh's (1993~) frame of reference model, partialing out the effects of year in school and gender increases the sizes of relations between the endurance measures and the PSDQ Endurance scale, although it has little effect on the pattern of relations. According to this frame of reference model, the relation between performance on a particular test and physical self-concept depends on how the performance compares with other students of the same gender and year in school, as well as absolute measures of performance. Thus, for example, being able to run 1.6 km in less than 10 minutes is likely to have a more positive effect on physical self-concept for a 12-year-old girl than for a 16-year-old boy because this performance would be relatively better for a younger girl than an older boy (see Marsh, 1993~). In contrast to the effects of gender and year in school, partialing out the effects of body composition reduces the size of these correlations (i.e., both objective measures and self-concept responses are negatively related to body composition). Although the juxtaposition of partialed and unpartialed measures complicates interpretations of the results somewhat, all three sets of correlations support the convergent and discriminant validity of the PSDQ responses. Physical Strength Measures of physical strength are typically classified as explosive strength, dynamic strength, and static strength, although it is difficult to distinguish empirically between explosive and dynamic strength (Marsh, 1993b; also see Fleishman, 1964). In the test battery considered here, the basketball throw, 50-m dash, and standing long jump are typically considered measures of explosive strength; the modified pull-up is a measure of dynamic strength; and there are no measures of static strength. However, the measures of explosive strength considered here may also have a substantial skill component; the modified pull-ups and standing long jump reflect some combination of strength as a function of body weight; and all four measures vary with gender and year in school. According to Marsh's (1993~) frame of reference model, controlling for the effect of gender and year in school should increase the size of correlations between these measures and the PSDQ Strength scale, whereas controlling for the effects of body composite may provide a more realistic indication of strength for those measures that depend upon lifting, moving, or propelling the body. All four measures of strength are significantly correlated with the PSDQ Strength scale, although the size of the correlation with the 50-m dash is not substantial. More critically, three of the criteria are more highly correlated with the PSDQ Sports Competence, Global Physical, Endurance, and Body Fat scales than the PSDQ Strength scale. Only the basketball throw is more highly correlated with the PSDQ Strength scale than with other PSDQ scales. However, the size and the pattern of results are altered substantially by controlling for gender, year in school, and body composition. More specifically, controlling for gender and year in school increases the size of correlations for the basketball throw and long jump, whereas controlling for body composition increases the size of the correlation for the standing long jump, modified pull-up, and 50-m dash. Of particular importance, all four strength measures are more highly correlated with the PSDQ Strength scale than

16 126 / Marsh other PSDQ scales when partial correlations are considered. Although the standing long jump is most highly correlated with the PSDQ strength scale when gender, year in school, and body composite are controlled, this measure is also substantially correlated with the PSDQ Sports Competence and, interestingly, the PSDQ Coordination scale. In summary, the results of the strength measures provide reasonable support for the convergent and discriminant validity of the PSDQ Strength scale after controlling for the effects of gender, year in school, and body composite. Flexibility The sit-and-reach test was the only measure of flexibility included in the physical fitness battery. This measure is significantly correlated with the PSDQ Flexibility scale and substantially more highly correlated with this scale than other PSDQ scales. Controlling for gender and year in school increases the size of this relation slightly, whereas controlling for the additional effects of body composition reduces it slightly. In summary, these results provide support for the convergent validity and discriminant validity of the PSDQ responses. Demographic Covariates Gender and year in school are not actually criteria for evaluating the construct validity of the PSDQ scales, but nevertheless it is interesting to evaluate these relations. There is a reasonably consistent pattern of modest declines in the PSDQ scales with increasing year in school, although this effect is only significant for three of the PSDQ scales. Girls tend to have lower PSDQ ratings, but these effects are not large and only reach statistical significance for five scales (Physical Appearance, Body Fat, Endurance, Sports Competence, and Global Physical). The Year-in-School x Gender interaction is statistically significant for three of the PSDQ scales (Physical Appearance, Endurance, and Strength). In each case, gender differences increase somewhat with year in school, although this effect is only substantial for Physical Appearance. The slight decline in self-concept with year in school during this early adolescent period is consistent with other self-concept research (e.g., Marsh, 1989) as are the lower scores for girls on physical self-concept scales. In this respect it could be argued that these differences also support the construct validity of PSDQ responses. It is particularly interesting, however, that the largest differences are in the areas of Physical Appearance and Body Fat rather than, for example, Strength. Because individuals tend to evaluate their physical characteristics in relation to those of other individuals of the same gender and year in school, the substantial differences in physical measures of strength are not reflected in gender differences in Strength self-concept. However, the results suggest that women have much more demanding standards of physical appearance and body fat than men (see Marsh & Roche, in press-b). Discussion The purpose of the present investigation is to evaluate support for the constmct validity of PSDQ responses in relation to external validity criteria reflecting body composition, physical activity, and other components of physical fitness. A priori predictions were made as to which PSDQ scale should be most highly corre-

17 Psysical Self-Description Questionnaire lated with each external criterion. There was good support for the convergent validity of the PSDQ responses in that all of the predicted correlations were statistically significant and most were substantial. There was also reasonable support for the discriminant validity of the PSDQ responses in that most of the predicted correlations were larger than other correlations involving the same external validity criterion. Taken together, these results provide good support for the construct validity of the PSDQ responses. There are, however, a number of features of the results that warrant additional discussion and, perhaps, further research. The juxtaposition of the PSDQ Body Fat and Appearance scales and their relations to body composition and silhouette ratings warrants further discussion. An important aspect of the design of the PSDQ was to include separate scales to represent Body Fat and Physical Appearance (Marsh et al., 1994). The present results provide very strong support for this separation. In particular, the silhouette ratings and the body composition measures are substantially more highly correlated with the PSDQ Body Fat scale than the PSDQ Physical Appearance scale. It is also interesting to note that there is a substantial correlation between the silhouette ratings and the PSDQ Body Fat scale even after partialingout the effects of the body composition measures. This finding may not be surprising in that both the silhouette ratings and PSDQ Body Fat responses are based on self-perceptions of being overweight, whereas body composition is based on objective measures. Hence, self-perceptions of being overweight are based on more than the objective measures of body composition. This result may also be consistent with the finding that the difference between the actual and ideal silhouette rating is more highly correlated with the PSDQ Body Fat and Physical Appearance scales than is the actual silhouette rating. This suggests that internal standards of what is ideal contribute to self-perceptions of Body Fat as well as actual perceptions (also see Marsh & Roche, in press-b). Although beyond the scope of this study, an important direction for further research is to explore sources of Body Fat self-concept that are not explained by objective body composition measures and why body composition measures are not more highly correlated with Physical Appearance self-concept and Global Esteem using, perhaps, a blend of quantitative and qualitative approaches. Frame-of-reference effects play an important role in interpreting relations between PSDQ responses and the external validity criteria. Hence, it is not objective characteristics per se, but interpretations of those characteristics in relation to some frame of reference that is a basis for forming self-concepts. The same objective characteristics may lead to very different self-concepts depending on the frames of reference used to evaluate them. One type of frame of reference effect has already been discussed for the silhouette ratings in that actual-ideal discrepancy scores were more highly correlated with Body Fat and Physical Appearance self-concepts than actual ratings alone. Hence, internal standards of what is "ideal" provide one potential source of information against which to evaluate objective measures. A second type of frame of reference effect involves the performances of other students who are the same gender and year in school. Consistent with predictions from Marsh (1993c), controlling for the effects of gender and year in school systematically increased the sizes of relations between PSDQ scales and performances that vary substantially with gender and year in school. Hence, the relative performances of other students of the same gender and year in school provide another potential source of information against which to evaluate objective measures.

18 128 / Marsh Although not pursued in this study, the exploration of the frames of reference used by elite athletes is likely to be a particularly fruitful direction of further research. Research into the big-fish-little-pond effect in the academic arena suggests that students tend to have lower academic self-concepts when they attend academically selective high schools and that the lower academic self-concepts may undermine the potential advantages of attending academically selective schools (Marsh, 1990, 1993a). Marsh, Perry, Horsely, and Roche (1995) discuss preliminary evidence suggesting that a similar frame of reference phenomena may affect elite athletes in elite athletic settings. In fact, one rationale for an emphasis on personal bests (an internal frame of reference that need not depend on the performance of other athletes) may be to avoid the potentially negative consequences of - - frame-of-reference effects resulting from social comparison processes. - It is also relevant to explore further the relatively modest support for the construct validity of PSDQ responses in relation to the strength measures. The sizes of the zero-order correlations were modest, perhaps reflecting the skill component in these measures and suggesting that a better selection of strength indicators is needed. Despite these limitations, however, the partial correlations controlling for gender, year in school, and body composite were better than the zero-order correlations. Controlling for the effect of the body composite improved correlations for the modified pull-up, standing long jump measures, and to a lesser extent, the 50-m dash. This pattern of results is reasonable since each of these tasks requires students to lift or propel their bodies. Also, controlling for the effects of gender and year in school &roved correlations for the basketball throw and standing long jump, and this is consistent with the proposal that the skills underlying these measures are evaluated in relation to other students of the same gender and year in school. Nevertheless, it is surprising that such a tangible characteristic as physical strength did not result in very large correlations between the physical strength measures and Strength self-concept. Interestingly, in apparent contrast to these findings, support for the convergent and discriminant validity for the PSDQ Strength scale was among the strongest of any of the PSDQ scales in the Marsh et al. (1994) MTMM study of three physical self-concept instruments. This suggests the possibility that self-perceptions of strength as embodied in all three physical self-concept scales may reflect some underlying characteristics that are not adequately represented by the dynamic and explosive strength measures considered here. From this perspective it is unfortunate that there were no measures of static strength included in the battery, as these might be more clearly related to the PSDQ Strength responses. A relevant direction for further research is to evaluate Strength self-concept in relation to a wider variety of strength measures and, perhaps, to explore further what characteristics students are using as a basis for forming Strength self-concept responses. It is also relevant to note several limitations of the present investigation. First, there were no external validity criteria that were predicted to be most highly correlated with the PSDQ Coordination, Health, Sports Competence, Global Physical, and Esteem scales. It was predicted, however, that the Global Physical and, to a lesser extent, the Sports competence scales would be substantially correlated with most of the external validity criteria, and there is support for this expectation. The PSDQ Coordination scale was not predicted a priori to be most highly correlated with any of the external criteria. Not surprisingly, however, it was mod-