APFIVE A researcher compares accident rates between two departments using monthly data collected consecutively. However, the data for one department may suffer from autocorrelation. What error did the researcher make?
Monthly Accident Data (Example):
Month | Dept 1 Accidents | Dept 2 Accidents
1 | 13 | 8
2 | 11 | 7
3 | 12 | 7
… | … | …
(Note: Consecutive months data may exhibit time-dependent patterns.)
They mistakenly used a paired t-test for independent departmental data.
They averaged the accident numbers over months incorrectly, thereby distorting the standard deviation.
They assumed that a larger sample size ensures independence, regardless of time-series effects.
They failed to account for the lack of independence due to autocorrelation in the sequential monthly data, which violates a key assumption of the two-sample t-test.
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