Practice question · Sort into groups
Sort each reading of a 95% confidence interval for the mean.
Groups: Correct interpretation · Incorrect interpretation
- There is a 95% chance the true mean is inside this interval
- 95% of the data values lie inside the interval
- This interval either contains the true mean or it does not
- Repeat the study many times and 95 intervals in 100 would hold the true mean
Hints
- A correct reading never assigns a probability to one already-computed interval.
- The interval estimates the MEAN, not the spread of the individual data.
Show the answer
Correct interpretation: Repeat the study many times and 95 intervals in 100 would hold the true mean, This interval either contains the true mean or it does not
Incorrect interpretation: There is a 95% chance the true mean is inside this interval, 95% of the data values lie inside the interval
Why
The confidence level describes the method's long-run success rate. Item 3 confuses an interval for the mean with an interval for the data, since the interval is only a few standard errors wide, it typically contains far less than 95% of the individual values.
Practise Confidence Intervals and Estimation
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