Why did the scientists use mice of the 'same age, size, health, and sex' for both groups?

Question

BlackTom AI · Accepted Answer

Controlling variables prevents alternative explanations for the observed effect, so the researchers matched mice on age, size, health, and sex.

1) Relevant knowledge points and concepts
- Independent variable: the factor deliberately changed by researchers (here, the type of diet).
- Dependent variable: what is measured to see the effect (here, mice growth).
- Controlled variables (constants): characteristics kept the same across groups to prevent confounding (age, size, health, sex).
- Confounding variable: an uncontrolled factor that could also cause changes in the dependent variable, undermining causal inference.

2) Step-by-step reasoning
Step 1: Identify the independent variable — diet (different diets given to two groups).
Step 2: Identify the dependent variable — growth of the mice.
Step 3: Identify possible confounders — differences in age, size, health, or sex can independently affect growth.
Step 4: To isolate the effect of diet, the researchers keep those potential confounders the same across groups (i.e., use mice matched for age, size, health, sex).
Step 5: If mice differ only by diet, then any systematic difference in growth is much more likely due to diet rather than to other characteristics.

3) Intermediate logical steps (illustrative)
- If older mice tend to grow more slowly, and Group A happens to have older mice, then observed differences could reflect age rather than diet.
- By matching ages, that alternative explanation is removed.
- Same logic applies to size, health, and sex (sex differences can produce different growth rates).

4) Why the correct answer is correct
Answer c states that matching mice ensures differences in growth are likely due to diet and not other factors. This directly captures the purpose of controlling variables: to reduce confounding and strengthen causal inference that the independent variable (diet) caused the observed change in the dependent variable (growth).

5) Why the other options are incorrect
- a. Matching animals does not make the experiment take less time; it addresses validity, not duration.
- b. Matching reduces the number of varying factors (confounders); it does not increase independent variables.
- d. Matching does not eliminate the need for a control group; a control group is still required to compare effects of different diets.

Conclusion: Therefore, the best answer is c. This matches the provided correct answer.

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