Rounding Rules for Confidence Intervals

1. When you are given a list of raw data you should round the mean and standard deviation to 1 more decimal place than what the data has.
    If your data has no decimals you round to 1 decimal place.
    If your data has 1 decimal place you round to 2 decimal places.
    If your data has 2 decimal places you round to 3 decimal places.
    If your data has 3 decimal places you round to 4 decimal places.

2. When calculating confidence intervals for the mean (using z or t), round your margin of error ( E ) to match the number of decimal places in the standard deviation.

3. When calculating confidence intervals for the proportion ( z ), round your margin of error ( E ) and the sample proportion (p hat) to 3 decimal places.

4. When calculating confidence intervals for the standard deviation or variance ( X2 ), round your margin of error ( E ) to match the number of decimal places in the standard deviation.

5. When finding the sample size round n to the next larger whole number.

Type of information
Rounding rules
 Raw data
One additional decimal place beyond  your data.
 Margin of Error ( E )
Match the number of decimal places in the standard deviation.
 Proportions ALWAYS round to three decimal places.
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