4.1.4 How Precise?

Determine what level of precision is appropriate.  Should you report dollars and cents? Should you round to whole dollars or even to the nearest $10 or $100? How many decimal places should you report?

The answer depends on the precision of the data and on how the data will be used.

Two or fewer decimal places will often be sufficient.

If the data are based on opinion or estimates, results with several decimal places are too precise. (See example at right.)

If you are providing estimates or ranges, rounded numbers are more acceptable.

More precision is needed if

• the decision requires an exact number,
• the values are part of a total (i.e., must sum to 100%), or
• the values are part of a calculation where rounding could make a difference in later results.