Base rates of "10 to 11" clocks in Alzheimer's and Parkinson's disease.

We extended the work of Rouleau et al. (I. Rouleau, D. P. Salmon, N. Butters, C. Kennedy, & K. McGuire, Quantitative and qualitative analyses of clock drawings in Alzheimer's and Huntington's disease. Brain and Cognition, 18, 1992, 70-87) and Ryan et al. (J. J. Ryan, S. J. Lopez, & S. W. Sumerall, Base rate of "10 to 11" clocks among patients referred for neuropsychological evaluation. Perceptual and Motor Skills, 81, 1995, 1138) by providing base rates for "10 to 11" clocks in samples of healthy elderly (n = 168), Alzheimer's disease (AD; n = 81), and Parkinson's disease (PD; n = 105). Groups were comparable in age and education. Stimulus bound clocks occurred in 3.0% of controls, 30.9% of AD, 5.7% of PD, and 10.2% of the combined sample. The 10.2% base rate is consistent with Ryan et al. for a mixed sample and Rouleau et al. for healthy elderly and patients with AD or Huntington's disease.