title: Reliability of delirium rating scale (DRS) and delirium rating scale-revised-98 (DRS-R98) using variance-based multivariate modelling.
abstract: Delirium's characteristic fluctuation in symptom severity complicates the assessment of test-retest reliability of scales using classical analyses, but application of modelling to longitudinal data offers a new approach. We evaluated test-retest reliability of the delirium rating scale (DRS) and delirium rating scale-revised-98 (DRS-R98), two widely used instruments with high validity and inter-rater reliability. Two existing longitudinal datasets for each scale included DSM-IV criteria for delirium diagnosis and repeated measurements using the DRS or DRS-R98. To estimate the reliability coefficients RT and RΛ for each scale we used a macros provided by Dr. Laenen at http://www.ibiostat.be/software/measurement.asp. For each dataset a linear mixed-effects model was fitted to estimate the variance-covariance parameters. A total of 531 cases with between 4 and 9 measurement points across studies including both delirious and non-delirious patients. Comorbid dementia in the datasets varied from 27% to 55%. Overall RT for the DRS were 0.71 and 0.50 and for DRS-R98 0.75 and 0.84. RΛ values for DRS were 0.99 and 0.98 and for DRS-R98 were 0.92 and 0.96. Individual RT measures for DRS-R98 and DRS across visits within studies showed more range than overall values. Our models found high overall reliability for both scales. Multiple factors impact a scale's reliability values including sample size, repeated measurements, patient population, etc in addition to rater variability.
authors.affiliation: Research and Academic Institute of Athens, Greece. dimaadamis@yahoo.com
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Adamis
authors.forename: Chantal J
authors.initials: CJ
authors.lastname: Slor
authors.forename: Maeve
authors.initials: M
authors.lastname: Leonard
authors.forename: Joost
authors.initials: J
authors.lastname: Witlox
authors.forename: Jos F M
authors.initials: JF
authors.lastname: de Jonghe
authors.forename: Alastair J D
authors.initials: AJ
authors.lastname: Macdonald
authors.forename: Paula
authors.initials: P
authors.lastname: Trzepacz
authors.forename: David
authors.initials: D
authors.lastname: Meagher
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003693:Delirium / Q000175:diagnosis* / Q000453:epidemiology; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015233:Models, Statistical; D019370:Observation; D011569:Psychiatric Status Rating Scales; D015203:Reproducibility of Results; D012720:Severity of Illness Index