View Full Version : Significant digits - a Quiz for our community

05-21-2007, 12:34 AM
Hi everyone,

This is general question relevant to a lot of our research. It should
be simple, but I don't recall the answer.

How many digits should be used in reporting data?

Here is an example. A biomechanist is trying to show a difference
between Technique A and Technique B. He/she recruits 36 subjects and
records each one of them performing both techniques, using equipment
that measures each person to the nearest 0.1 unit. How many decimal
places should be used in reporting the data? I can make a "common
sense" determination, but is there some accepted procedure or guideline?

Example data:


Subject 1: 13.3 units

Subject 2: 35.0 units

Subject 3: 22.2 units

Subject 36: 18.4 units


Subject 1: 12.9 units

Subject 2: 35.0 units

Subject 3: 21.9 units

Subject 36: 18.5 units

Even though the mean within-subject difference is less than 0.1 units, a
paired t-test reveals a statistically significant difference.

Technique A mean: 25.33333 units

Technique B mean: 25.36170 units

Average difference : 0.02837 units

Paired t-test p-value: 0.035

How many decimal places would you use in reporting these mean values and
difference in your paper? Why?

Thanks in advance,

- Glenn S. Fleisig, Ph.D.

Glenn S. Fleisig, Ph.D., Smith & Nephew Chair of Research
American Sports Medicine Institute
833 St. Vincent's Drive, Suite 100
Birmingham, AL 35205
(email) glennf@asmi.org
(tel) 205-918-2139