COHORT EFFECTS - A POSSIBLE LIMITATION TO THE INTERPRETATION OF LONGITUDINAL-STUDIES

The possible limitation that cohort effects could impose upon the inte rpretation of longitudinal research has been examined, taking data on the standing height and the maximal oxygen intake of 546 primary schoo l students participating in the Trois Rivieres mixed-longitudinal stud y of enhanced physical education programs (295 experimental and 251 co ntrol subjects of both sexes). Over the short period of the study (max imum intercohort time span of 4 years), no significant differences in standing height were observed. In the larger urban community of Trois Rivieres (population about 100,000), where the program of additional p hysical education was very successful in augmenting the maximal oxygen intake of the experimental students, a statistically significant inte rcohort difference of aerobic power developed among control students o ver the span of 3-4 years. However, in Pont Rouge (population about 5, 000), where the added physical education had a smaller impact upon the maximal oxygen intake of the experimental students, there were no sig nificant intercohort differences. Among possible explanations of the i ntercohort difference seen in Trois Rivieres, the most likely seems an indirect effect of the experimental physical education program upon t he patterns of habitual physical activity in the control population. ( C) 1993 Wiley-Liss, Inc.