Assessment of delirium is performed with a variety of instruments, making comparisons between studies difficult. A conversion rule between commonly used instruments would aid such comparisons. The present study aimed to compare the revised Delirium Rating Scale (DRS–R98) and Memorial Delirium Assessment Scale (MDAS) in a palliative care population and derive conversion rules between the two scales.

Both instruments were employed to assess 77 consecutive patients with DSM–IV delirium, and the measures were repeated at three-day intervals. Conversion rules were derived from the data at initial assessment and tested on subsequent data.

There was substantial overall agreement between the two scales [concordance correlation coefficient (CCC) = 0.70 (CI95 = 0.60–0.78)] and between most common items (weighted κ ranging from 0.63 to 0.86). Although the two scales overlap considerably, there were some subtle differences with only modest agreement between the attention (weighted κ = 0.42) and thought process (weighted κ = 0.61) items. The conversion rule from total MDAS score to DRS–R98 severity scores demonstrated an almost perfect level of agreement (r = 0.86, CCC = 0.86; CI95 = 0.79–0.91), similar to the conversion rule from DRS–R98 to MDAS.

Overall, the derived conversion rules demonstrated promising accuracy in this palliative care population, but further testing in other populations is certainly needed.