2.2. Exposure

At the subject hospital, patients were routinely screened for cognitive impairment before admission using the Dementia Assessment Sheet for Community‐based Integrated Care System 21‐items (DASC‐21, Appendix A). 23 A previous study reported that the DASC‐21 has adequate reliability and validity to evaluate cognitive and daily functioning impairments, detect dementia, and assess dementia severity in community‐dwelling older adults in Japan. 24 In that study, Cronbach alpha for DASC‐21 as evaluated by trained nurses was estimated to be 0.934, and DASC‐21 scores were significantly correlated with the Clinical Dementia Rating total and box scores, the Mini‐Mental State Examination, and the Frontal Assessment Battery. 24 The 21 items of DASC‐21 are answered using a scale ranging from 1 to 4 (total score range: 21‐84), and a total score of 31 or more indicates a risk of dementia. 23

In this study, cognitive impairment severity was derived from the DASC‐21 data and classified into four categories in accordance with the DASC‐21 assessment manual: (1) normal cognition (ie, no cognitive impairment), (2) minor cognitive impairment, (3) moderate cognitive impairment, and (4) severe cognitive impairment (Figure 1). 23 This category of cognitive impairment severity was based on the clinical status of impairment in cognitive function and functioning in daily life using the total DASC‐21 score and responses to the items about remote memory (Question 3), space orientation (Question 5), social common sense (Question 9), and physical ADL (Question 16‐21). 23 A total score of 30 or less on the DASC‐21 indicated “normal cognition.” A total score of 31 and above and a score of 1 or 2 for Questions 3, 5, 9, and 16‐21 indicated “minor cognitive impairment.” A total score of 31 and above and a score of 3 or 4 for at least one item (but not all) for Questions 3, 5, 9, and 16‐21 indicated “moderate cognitive impairment.” A total score of 31 and above and a score of 3 or 4 for all of these questions indicated “severe cognitive impairment.” The DASC‐21 is administered to each patient's family members or caregivers to assess the patient's cognitive function during the month before admission. If a patient did not have any family member or caregiver available to answer, they completed the DASC‐21 themselves or through a proxy such as a care manager or care worker.

Categorization of cognitive impairment severity. Questions: No. 3 (remote memory): “Does he/she forget his/her own birth date?”; No. 5 (spatial orientation): “Does he/she forget where he/she is?”; No. 9 (social common sense): “Can he/she select his/her own clothes appropriately according to the season or situation?”; Nos. 16‐21 (physical activities of daily living): “Can he/she take a bath by himself/herself?”, “Can he/she change clothes by himself/herself?”, “Can he/she use the toilet by himself/herself?”, “Can he/she take care of his/her own appearance?”, “Can he/she eat on his/her own?”, and “Can he/she move around the house by himself/herself?”. DASC‐21, Dementia Assessment Sheet for Community‐based Integrated Care System‐21 items