The British Picture Vocabulary Scale: constructing confidence intervals to evaluate change.

The practitioner is often faced with the situation where a client has been administered a test more than once, and it must be determined whether variation in the scores obtained is either due to real change or merely reflects imprecision in measurement. This paper offers a table of standard errors of prediction, and confidence levels based thereon, which can help in making this decision where the British Picture Vocabulary Scale is used. The table is based on the normative data provided in the manual.