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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.

Step by step solution

01

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.

02

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.

03

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.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Body Composition

Body composition refers to the different components that make up a person's body, primarily fat, muscle, bone, and water. In studying body composition, researchers often focus on the percentage of body fat, as it plays a significant role in health and fitness.
For instance, in the study mentioned, the researchers measured the body fat percentage to assess how physical activity might affect it.

• High body fat percentage can increase the risk of various health problems.
• Low body fat can sometimes indicate muscle loss or other health issues.

By measuring and comparing body fat percentages, scientists can gather insights into health trends and outcomes related to lifestyle factors like physical activity.

Explanatory and Response Variables

When analyzing studies, it's crucial to identify the explanatory and response variables, as they help us understand the relationship being explored.
In our example, the researchers aimed to see how different levels of physical activity affect body fat percentage.

• The explanatory variable here is the level of physical activity (active or sedentary).
• The response variable is the body fat percentage.

Explanatory variables are sometimes called independent variables because they are considered the cause that influences another variable.
The response variable, often known as the dependent variable, is the effect or outcome influenced by the explanatory variable.
Understanding these can help clarify the purpose of the study and guide further analysis.

Exploring Causal Relationships

Causal relationships refer to a cause-and-effect link between two variables. In scientific studies, proving a causal relationship means showing that one variable directly causes changes in another.
In the context of our study, while there is an association between physical activity level and body fat percentage, proving causation is more complex.

• In observational studies, like the one described, researchers simply observe and measure variables as they exist without intervening.
• This limits the ability to establish causation because other factors (confounding variables) might influence the results.

For example, factors like diet, genetics, or other lifestyle choices could impact body fat percentage besides just physical activity.
Consequently, while the study indicates a relationship, it cannot, by itself, establish that exercise causes lower body fat.
Experiments with controlled environments would be necessary for stronger causal conclusions.