The effect of awareness of measurement error on physical therapists' confidence in their decisions

Program in Physical Therapy, Northwestern University Medical School, Chicago, IL 60611.

This study examined whether physical therapists understand the meaning of measurement error and whether information about measurement error affects their decisions. One of four versions of two physical therapy problems was mailed to 500 randomly selected physical therapists. Therapists were asked to define reliability and error of measurement, to estimate the error of measurement of two assessments, and to make decisions about an intervention based on specific measurements. They were also asked to rate their confidence in those decisions. Problems varied on the presence or absence of measurement information and on the difference between an observed measurement and a criterion measurement against which the observed measurement must be compared to make a decision. The response rate was 62%; respondents represented a typical profile of practicing physical therapists. The therapists understood reliability, but they did not correctly describe the relationship between reliability and error of measurement. Their estimates of the error of measurement of the two assessments were reasonable for only one procedure. The presence or absence of measurement information and difference between observed and criterion measurements affected their confidence, albeit inappropriately, in only one problem. Confidence was not affected by the therapists' level of experience, type of reading, formal study, or degree earned. Therapists responded to the two problems differently. The problems involved different measures, roles, utilities, and structures. The process of decision making does not generalize to all decision types. Measurement principles and strategies of use in decision making must be emphasized in physical therapy curricula so that physical therapists can consider the quality of their assessment data in making clinical decisions.

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