• Natalie A de Morton, Megan Davidson, and Jennifer L Keating.
• School of Primary Health Care, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Victoria, Australia; The Northern Clinical Research Center, Northern Health, Epping, Victoria, Australia. natalie.demorton@nh.org.au.
• Physiother Res Int. 2011 Sep 1; 16 (3): 159-69.

BackgroundThe de Morton Mobility Index (DEMMI) is an instrument that accurately measures the mobility of older people across clinical settings.PurposeTo report the multiple reliability studies conducted during the development and validation of the DEMMI.MethodsIntra-rater and inter-rater reliability studies were conducted for the DEMMI in two independent samples (development and validation samples) of older acute medical patients (aged 65 years or older). Inter-rater reliability studies were conducted between the test developer (a physiotherapist) and another experienced physiotherapist. Order of assessor administration was randomized by a coin toss. Patients who were fatigued after the first assessment were excluded from the inter-rater reliability study. Intra-rater reliability studies included participants with 'unchanged' mobility status between hospital admission and discharge. Scale reliability estimates were expressed as the minimal detectable change with 90% confidence (MDC90 ). Item reliability was calculated using Kappa statistics and absolute percentage agreement.ResultsThe MDC90 for the DEMMI development sample was 9.51 points (95% confidence interval [95% CI], 5.04-13.32; n=21) and 7.84 (95% CI, 4.34-11.65; n=16) on the 100-point interval DEMMI scale for the inter-rater and intra-rater reliability studies, respectively. Similar estimates were obtained for the DEMMI validation samples of 8.90 (95% CI, 6.34-12.69; n=35) and 13.28 points (95% CI, 8.08-20.87; n=19). Items were not excluded from the DEMMI based on the results of item reliability.ConclusionReliability estimates for the DEMMI were consistent across independent samples of older acute medical patients using different reliability study methodology. Error represents approximately 9% of the DEMMI scale width.Copyright © 2010 John Wiley & Sons, Ltd.

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