Note:

- If the data is comes from a normal distribution, then the t-test and the confidence interval are exact.
- If the data doesn’t come from a normal distribution, then the t-test and confidence interval will be approximate if
**n < 15**and the**data are close to normal**. If the data are clearly not normally distributed or outliers exist, do not use the t-test.**n ≥ 15**, then the t-tests can be used**except**in the case that the data contains**outliers**or the data is**strongly skewed**.**n ≥ 40**(large samples), then the**t-tests can be used**even for skewed distributions and the**results**will be**approximate but fairly accurate**.