title: Defining the minimal detectable change in scores on the eight-item Morisky Medication Adherence Scale.
abstract: BACKGROUND
  Self-report scales are used to assess medication adherence. Data on how to discriminate change in self-reported adherence over time from random variability are limited.
  
  
  OBJECTIVE
  To determine the minimal detectable change for scores on the 8-item Morisky Medication Adherence Scale (MMAS-8).
  
  
  METHODS
  The MMAS-8 was administered twice, using a standard telephone script, with administration separated by 14-22 days, to 210 participants taking antihypertensive medication in the CoSMO (Cohort Study of Medication Adherence among Older Adults). MMAS-8 scores were calculated and participants were grouped into previously defined categories (<6, 6 to <8, and 8 for low, medium, and high adherence).
  
  
  RESULTS
  The mean (SD) age of participants was 78.1 (5.8) years, 43.8% were black, and 68.1% were women. Overall, 8.1% (17/210), 16.2% (34/210), and 51.0% (107/210) of participants had low, medium, and high MMAS-8 scores, respectively, at both survey administrations (overall agreement 75.2%; 158/210). The weighted κ statistic was 0.63 (95% CI 0.53 to 0.72). The intraclass correlation coefficient was 0.78. The within-person standard error of the mean for change in MMAS-8 scores was 0.81, which equated to a minimal detectable change of 1.98 points. Only 4.3% (9/210) of the participants had a change in MMAS-8 of 2 or more points between survey administrations.
  
  
  CONCLUSIONS
  Within-person changes in MMAS-8 scores of 2 or more points over time may represent a real change in antihypertensive medication adherence.
authors.affiliation: University of Alabama at Birmingham, Birmingham, AL, USA. pmuntner@uab.edu
authors.forename: Paul
authors.initials: P
authors.lastname: Muntner
authors.forename: Cara
authors.initials: C
authors.lastname: Joyce
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Holt
authors.forename: Jiang
authors.initials: J
authors.lastname: He
authors.forename: Donald
authors.initials: D
authors.lastname: Morisky
authors.forename: Larry S
authors.initials: LS
authors.lastname: Webber
authors.forename: Marie
authors.initials: M
authors.lastname: Krousel-Wood
mesh_terms: D000368:Aged; D000959:Antihypertensive Agents / Q000627:therapeutic use; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D011795:Surveys and Questionnaires; D014894:Weights and Measures / Q000592:standards*; D016903:Drug Monitoring
chemical_list: D000959:Antihypertensive Agents