Understanding Statistical Concepts: Sample Size, Causation, Confidence Intervals, and Z-Scores
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1. The t-test is never valid if the sample size is small, say less than 30. (TRUE OR FALSE)
It can be valid if the sample is approximately normal.
2. The results of an observational study indicate that people who use vitamin supplements get fewer colds than people who don't. However, we can't conclude that vitamin supplements prevent colds because this type of study does not allow us to infer causation. (TRUE OR FALSE)
Only experimental designs can infer causation because it allows us to create treatment groups that are very similar.