Stanine width is about half a standard deviation.

• A. True
• B. False
• C. Not applicable
• D. Depends on norm group

Answer: (D)

Stanine scores are a nine-point scaled system that places equal-area segments of a norm-referenced distribution into nine bins. The boundaries between these bins are based on percentile cutpoints of the normative sample, not on fixed standard-deviation intervals.

Because those cutpoints are derived from the actual shape of the norm group’s distribution, the distance between stanines in standard-deviation units can vary. If the normative distribution is roughly normal, the widths may resemble about half a standard deviation, but this is only an approximation. For distributions that are skewed or have different dispersion, the actual SD width per stanine will shift.

So, whether stanine width is about half a standard deviation depends on the norm group used to create the stanine scale. That’s why the best answer is that it depends on the norm group.