Does scale length matter? A comparison of nine- versus five-point rating scales for the mini-CEX.
Educators must often decide how many points to use in a rating scale. No studies have compared interrater reliability for different-length scales, and few have evaluated accuracy. This study sought to evaluate the interrater reliability and accuracy of mini-clinical evaluation exercise (mini-CEX) scores, comparing the traditional mini-CEX nine-point scale to a five-point scale.


METHODS
The authors conducted a validity study in an academic internal medicine residency program. Fifty-two program faculty participated. Participants rated videotaped resident-patient encounters using the mini-CEX with both a nine-point scale and a five-point scale. Some cases were scripted to reflect a specific level of competence (unsatisfactory, satisfactory, superior). Outcome measures included mini-CEX scores, accuracy (scores compared to scripted competence level), interrater reliability, and domain intercorrelation.


RESULTS
Interviewing, exam, counseling, and overall ratings varied significantly across levels of competence (P < .0001). Nine-point scale scores accurately classified competence more often (391/720 [54%] for overall ratings) than five-point scores (316/723 [44%], P < .0001). Interrater reliability was similar for scores from the nine- and five-point scales (0.43 and 0.40, respectively, for overall ratings). With the exception of correlation between exam and counseling scores using the five-point scale (r = 0.38, P = .13), score correlations among all domain combinations were high (r = 0.46-0.89) and statistically significant (P < or = .015) for both scales.


CONCLUSIONS
Mini-CEX scores demonstrated modest interrater reliability and accuracy. Although interrater reliability is similar for nine- and five-point scales, nine-point scales appear to provide more accurate scores. This has implications for many educational assessments.
Cook
David A
DA
Division of General Internal Medicine and Office of Education Research, Mayo Clinic College of Medicine, Baldwin 4-A, 200 First Street SW, Rochester, MN 55905, USA. cook.david33@mayo.edu
Beckman
Thomas J
TJ
D002983:Clinical Competence; D004503:Education, Medical, Graduate / Q000379:methods / Q000592:standards*; D004521:Educational Measurement / Q000379:methods / Q000592:standards*; D006801:Humans; D007388:Internal Medicine / Q000193:education*; D007396:Internship and Residency / Q000379:methods / Q000592:standards*; D015203:Reproducibility of Results; D014743:Videotape Recording