A population based study on the intra and inter-rater reliability of the clock drawing test in Brazil: the Bambuí Health and Ageing Study.

Background: Reliability should be considered when selecting a scoring system since it influences validity. CDT reliability has rarely been assessed in population based studies and in developing countries. The aim of the present study was to determine intra and inter-rater reliabilities of the CDT scored by the Shulman (2000) method, in elderly with very low formal educational level from Brazil.

Methods: CDTs performed by a random sample of 202 subjects of a population-based cohort of elderly were scored on two occasions by the same rater and by two independent raters. Reliability was measured using the kappa statistic, weighted kappa and the intraclass correlation coefficient. Data were stratified according to gender, age and schooling level.

Results: Intra and inter-rater reliabilities were excellent when CDTs were classified as 'normal' (scores 4 or 5) or 'abnormal' (scores 0 to 3) (kappa = 0.99 and 0.94, respectively) and were in the good to excellent range when scored from 0 to 5 (kappa = 0.88 and 0.74, respectively). Difficulties in distinguishing between scores 4 and 5, and a low proportion of score 1 tests were found.

Conclusions: The CDT scored by the Shulman (2000) method appears to have good to excellent reliability in an elderly population with very low formal educational level. However, difficulties in distinguishing between scores 4 and 5, and a low proportion of score 1 tests suggest these scores may not be totally adequate for this population. Further studies are necessary to determine the consistency of our results in similar populations.