Reliability and acquiescence in the measurement of locus of control with adolescents and adults with mental retardation.

The locus of control construct has been useful for explaining individual and group variability in motivation, personality, and achievement. Despite a general agreement that people with mental retardation generally lack control in their lives, the construct has not been used to any meaningful extent to explain less than optimal life outcomes experienced by this group. One reason that this circumstance exists is that people with mental retardation often answer questions in an acquiescent manner, thereby jeopardizing the reliability and validity of the measure. The present study examined the reliability of one measure of locus of control, the Adult version of the Nowicki-Strickland Internal-External Scale, for 491 adults and adolescents with mental retardation and, using alternative forms of this scale, assessed the extent to which acquiescence contributes to externality in this population. Results from repeated-measures analysis of variance suggest that the acquiescence contributes nominally to measurement error with this population. Suggestions are made to improve reliability with the scale.