Question

To examine the effect of exercise on body composition, healthy women aged 35 to 50 were classified as either active (nine or more hours of physical activity per week) or sedentary ("Effects of Habitual Physical Activity on the Resting Metabolic Rates and Body Composition of Women Aged 35 to 50 Years," Journal of the American Dietetic Association [2001]: 1181-1191). Body fat percentage was measured, and the researchers found that this percentage was significantly lower for women who were active than for sedentary women. a. Is the study described an experiment? If so, what is the explanatory variable and what is the response variable? If not, explain why it is not an experiment. b. From this study alone, is it reasonable to conclude that physical activity is the cause of the observed difference in body fat percentage? Justify your answer.

Short answer

The study described is not an experiment but an observational study. The explanatory variable is the level of physical activity, and the response variable is body fat percentage. It's not reasonable to conclude from this study alone that physical activity is the cause of the observed difference in body fat percentage due to potential confounding variables.

Step-by-step solution

Identify the Type of Study

The first step is to identify whether this study is an experiment or not. In an experiment, the researchers deliberately manipulate (change/control) one variable to observe the effect on another variable. When reading through our exercise, the researchers did not manipulate women's exercise habits. Instead, they classified women as either active or sedentary based on their current lifestyles. Thus, this study is not an experiment but an observational study.

Identify Variables

Even though it's not an experiment, it's still important to identify the variables. The explanatory variable is physical activity level (active or sedentary), and the response variable is body fat percentage.

Evaluate Reasonability of Conclusion

In an observational study like this one, it's hard to definitively establish causal relationships. Although there's an observed difference in body fat percentage between active and sedentary women, it cannot be concluded solely from this study that physical activity is the cause. There could be various confounding variables, like diet or genetics, that also affect body fat percentage and were not controlled in this study. So, it's not reasonable to conclude that physical activity is the cause of the observed difference in body fat percentage from this study alone.