Question

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Explanation:

Analyze the statement

Using the Statistical Study Evaluation knowledge point

The statement claims: "It is proved beyond a doubt that vitamin C can reduce the severity of colds, because I controlled the experiment carefully for every possible confounding variable."

In experimental design, it is practically impossible to identify, let alone perfectly control or eliminate, every single potential confounding variable. Human biology and environmental factors introduce countless hidden variables. Therefore, claiming something is proved "beyond a doubt" based on controlling "every possible" confounding variable is logically flawed.

Evaluate the options

Using the Statistical Study Evaluation knowledge point

Let's evaluate the given choices based on scientific methodology:

• Option 1: "does not make sense because it is not always easy to discover confounding variables." This is correct because identifying and controlling all confounding variables is extremely difficult, making the claim of absolute proof unrealistic.
• Option 2: "does not make sense because confounding variables would not affect the reliability of the experiment." This is incorrect; confounding variables directly threaten internal validity and reliability.
• Option 3: "makes sense because confounding variables are the only reason an experiment's results could be doubted." This is incorrect; other issues like sample size, bias, and measurement errors also exist.
• Option 4: "makes sense because every possible confounding variable can be eliminated through careful study." This is incorrect; it is impossible to eliminate all confounding variables in human trials.

Thus, the statement does not make sense because discovering and controlling all confounding variables is not always feasible.

Answer:

• (A) does not make sense because it is not always easy to discover confounding variables. (Correct answer)
• (B) does not make sense because confounding variables would not affect the reliability of the experiment.
• (C) makes sense because confounding variables are the only reason an experiment's results could be doubted.
• (D) makes sense because every possible confounding variable can be eliminated through careful study.