Phasic influences on psychometric measures during the menstrual cycle: implications for the construct integrity of the locus of control dimension.

Thirty healthy female volunteers with normal menstrual cycles participated in a study to examine the influence of menstrual cycle phase on locus of control (LC) orientation. LC measures were taken on the follicular, luteal and premenstrual phase of the cycle. It was found that menstrual cycle phase had little effect on LC orientation suggesting that previously observed LC differences across the cycle in dysmenorrhea and premenstrual syndrome sufferers cannot be generalized to a normal non-clinical population. Surprisingly, it was further found that no significant statistical relationship was found between the two LC measures used, in spite of the finding that, individually, each LC measure intercorrelated highly significantly across the menstrual cycle. Since one of the LC scales was derived theoretically, and the other LC scale used was derived from clinical practice, the findings are discussed in relation to the theory-practice divide and the prima facie value of self-report LC measures.