To the Editor: In their study, Dr Yaffe and colleagues1 concluded that older women with sleep-disordered breathing are more likely to suffer cognitive decline. However, the patients in both study groups, with and without sleep-disordered breathing, had mild cognitive impairment at baseline (mean Mini-Mental State Examination [MMSE] scores of 25.1 and 24.9, respectively). Almost 5 years later, both groups received another cognitive assessment. The authors found 44.8% of women with sleep-disordered breathing developed mild cognitive impairment or dementia compared with 31.1% of those without it. Because patients in both groups started the study with mild cognitive impairment, what percentage developed dementia? How did the MMSE scores change over time? In addition, the authors used different instruments in the 5-year cognitive assessments, making it difficult to appreciate the difference between the 2 groups over time.