Vicki A Freedman1, Hakan Aykan, Linda G Martin. 1. Polisher Research Institute, Madlyn and Leonard Abramson Center for Jewish Life (formerly Philadelphia Geriatric Center), North Wales, Pennsylvania 19454, USA. vfreedman@abramsoncenter.org
Abstract
OBJECTIVES: This study explored whether previously reported declines in severe cognitive impairment were robust to cumulative effects of potentially confounding survey design issues. METHODS: Using the 1993 Asset and Health Dynamics of the Oldest Old study (n = 7,443) and 1998 Health and Retirement Survey (HRS; n = 7,624) the proportion of persons ages 70 and older with severe cognitive impairment was calculated under various assumptions about item nonresponse, differential loss to follow-up, and the size and composition of the nursing home population. Impairment was measured for self-respondents using a modified version of the Telephone Interview Cognitive Screen; for proxy respondents ratings of memory and judgment were used. Chi-square tests were adjusted to account for complex survey designs. RESULTS: Ignoring loss to follow-up, excluding nursing home residents, and assigning a low score to those refusing subscales yielded a statistically significant decline in severe cognitive impairment from 5.8% in 1993 to 3.8% in 1998, or an average annual decline of 6.9%. When cumulative effects of survey design issues were considered and design effects incorporated into statistical tests, statistically significant declines persisted, albeit at a reduced average annual rate, ranging from 2.5% to 6.9% per year. DISCUSSION: Previously reported improvements in severe cognitive impairment appear to be robust to a variety of specifications. Replication with future waves of the HRS and other data is warranted.
OBJECTIVES: This study explored whether previously reported declines in severe cognitive impairment were robust to cumulative effects of potentially confounding survey design issues. METHODS: Using the 1993 Asset and Health Dynamics of the Oldest Old study (n = 7,443) and 1998 Health and Retirement Survey (HRS; n = 7,624) the proportion of persons ages 70 and older with severe cognitive impairment was calculated under various assumptions about item nonresponse, differential loss to follow-up, and the size and composition of the nursing home population. Impairment was measured for self-respondents using a modified version of the Telephone Interview Cognitive Screen; for proxy respondents ratings of memory and judgment were used. Chi-square tests were adjusted to account for complex survey designs. RESULTS: Ignoring loss to follow-up, excluding nursing home residents, and assigning a low score to those refusing subscales yielded a statistically significant decline in severe cognitive impairment from 5.8% in 1993 to 3.8% in 1998, or an average annual decline of 6.9%. When cumulative effects of survey design issues were considered and design effects incorporated into statistical tests, statistically significant declines persisted, albeit at a reduced average annual rate, ranging from 2.5% to 6.9% per year. DISCUSSION: Previously reported improvements in severe cognitive impairment appear to be robust to a variety of specifications. Replication with future waves of the HRS and other data is warranted.
Authors: Kenneth M Langa; Eric B Larson; Jason H Karlawish; David M Cutler; Mohammed U Kabeto; Scott Y Kim; Allison B Rosen Journal: Alzheimers Dement Date: 2008-03-04 Impact factor: 21.566