91Ó°ÊÓ

Don't stop exercising! An investigation of the effect of different levels of physical activity was conducted on identical male twins in Finland. For each twin pair, although they had maintained the same activity level for most of their lives, one twin had significantly reduced his or her activity over the last few years due to work or family pressures. For each pair of twins, body fat percentage, endurance levels, and insulin sensitivity were measured. For the less active twin, the results showed greater body fat, worse endurance, and levels of insulin sensitivity displaying early signs of metabolic disease. 23 (a) What type of design is being used in this investigation? Give the explanatory and response variables. (b) Is this an experiment or an observational study? Why? (c) The article reports that the measurements were carried out blind. Explain what this means and why it is important.

Step by step solution

01

Identify the Study Design

The investigation involves comparing identical twins, where one twin has reduced his physical activity. This suggests a matched-pairs design, which is a type of observational study where subjects are paired based on shared variables—in this case, identical genetics—to control for confounding variables.

02

Determine Explanatory and Response Variables

The explanatory variable is the level of physical activity, specifically the reduction in activity for one twin. The response variables are the measurements taken: body fat percentage, endurance levels, and insulin sensitivity.

03

Classify the Study Type

This is an observational study because the researchers are observing natural variations in the levels of physical activity without manipulating them. Experiments require active intervention or manipulation by the researcher.

04

Explain the Importance of Blinding

Blinding means that the individuals measuring the outcomes did not know which twin was less active. This is crucial as it prevents measurement bias and ensures objectivity, meaning that pre-existing beliefs do not influence the results.

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Key Concepts

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

Matched-Pairs Design

In the study involving identical male twins in Finland, a matched-pairs design was used. This type of study design centers around pairing subjects who are alike on many characteristics, except for the treatment or condition being studied. Here, identical twins were perfect candidates for this design because they share the same genetics and likely many environmental factors. The only major difference was the reduction in physical activity in one of the twins, which allowed researchers to compare how this variation affected key health markers. Matched-pairs design helps control for confounding factors because pairs already account for shared variables, thus making it possible to better detect genuine effects of the condition under study, such as changes in physical activity.

Explanatory and Response Variables

In research, understanding the relationship between variables is crucial. In this study, the explanatory variable is the level of physical activity, specifically the reduction in activity for one of the twins in each pair. The researchers were interested in seeing how this would influence certain health metrics.

The response variables included:

• Body fat percentage
• Endurance levels
• Insulin sensitivity

These response variables were the outcomes measured to observe the health impact of decreased physical activity. Observing these variables helps in understanding the effects and associations tied to levels of physical activity.

Measurement Blinding

Measurement blinding refers to ensuring that the individuals who measure the outcomes do not know which participants belong to which group. In this study, the measurements (such as body fat percentage, endurance, and insulin sensitivity) were carried out blindly. This is critical to prevent measurement bias—a situation where the research outcomes might be skewed by someone’s expectations. Blind measurements help maintain objectivity and ensure that results are driven by actual data, not the preconceived beliefs of those measuring the data. This practice increases the validity and reliability of the study results by reducing the influence of bias.

Confounding Variables Control

In any observational study, controlling for confounding variables is crucial. Confounding variables are external factors that could potentially affect the study's outcome. This matched-pairs study, by design, minimizes the impact of confounding variables because the twins are genetically identical and likely share similar environmental experiences. This control is further enhanced by focusing on a single differing variable—physical activity reduction. By maintaining control over potential confounders, researchers can attribute differences in response variables more confidently to the change in the explanatory variable.