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Swedish Twin Registry
Average Follow-up Time Detail
The average follow-up time was not reported. Leisure activity was assessed in 1967. Study participants received follow-up assessments for dementia either as part of the OCTO-TWIN study, which began in 1991, or as part of the pilot phase of the Study for Dementia in Swedish Twins, which began between 1987 and 1991.
In the OCTO-TWIN study, individuals could have received up to four dementia assessments over the study follow-up period (1991-1999). In the pilot phase of the Study of Dementia in Swedish Twins, individuals received one dementia assessment.
Crowe et al., report that 16,824 (81%) of the 20,770 Swedish Twin Registry members who were sent the questionnaire in 1967 responded to the leisure activity items. Of these 16,824 people, 640 were evaluated for dementia in OCTO-TWIN, while 1496 were assessed for dementia, in the pilot phase of the Study of Dementia in Swedish Twins. Therefore, overall, 2136 of the 16,284 (12.7%) of those who had leisure activity data were assessed for dementia in these studies.
Participants enrolled as part of the "old cohort" of the Swedish Twin Registry were sent a questionnaire in 1967 assessing their participation in leisure activities prior to age 40. Using data from all responding twins, the investigators conducted an exploratory factor analysis and grouped questionnaire items based on their factor loadings into three factors: "intellectual-cultural", "self-improvement", and "domestic". The "intellectual-cultural" factor incorporates the following four items: (i) reading, (ii) listening to the radio or watching television, (iii) making social visits, and (iv) attending cultural activities (e.g., theatre or cinema).
"Members of the STR who were born between 1886 and 1925 were sent a questionnaire in 1967 that included questions on leisure activities. Participants answered 11 items indicating whether or not, before the age of 40, they were regularly involved in each of these activities: reading, listening to the radio or watching television, social visits, cultural activities such as theatre and cinema, hobbies, home and family, clubs and organizations, studies, house and gardening, outdoor activities, and playing sports. An exploratory factor analysis was performed in order to reduce the number of leisure activity variables and to create a more parsimonious model of activity engagement..."
No data on ethnicity was reported. All participants reside in Sweden.
The value reported here is the average age of the study population in 1967, when the leisure questionnaire was completed. As noted above, assessments for dementia occur much later in life, either as part of the OCTO-TWIN baseline or follow-up assessments between 1991 and 1999, or as part of the pilot phase of the Study of Dementia in Swedish Twins between 1987 and 1991.
Screening and Diagnosis Detail
Mini-Mental State Examination (Folstein 1975)
Telephone assessment of dementia
National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association Criteria (McKhann 1984)
Total dementia diagnosis:
"Case ascertainment for the Study of Dementia in Swedish Twins used a two-step process: an initial screening and then a comprehensive clinical evaluation that resulted in a consensus diagnosis. The initial screening used the Mini-Mental State Examination (MMSE; Folstein, Folstein,&McHugh, 1975) for those who were visited by the SATSA assessment team and a telephone screening protocol for those who were not visited...Subsequently, dementia suspects (i.e., those who scored below preestablished norms for cognitive impairment on MMSE or the telephone screening protocol) and their twin partners were evaluated for dementia by an assessment team that consisted of a nurse, a psychologist, and a physician. The protocol used by this team parallels the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD; Morris et al., 1989) procedures for physical and neurological evaluations, laboratory tests, informant interview, neuropsychological testing, and neuroimaging. Findings of the assessment team were discussed at a consensus diagnosis conference attended by the clinicians and chaired by a psychologist who had not met the participant. Clinical dementia diagnoses were based on the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1987) criteria for dementia and the National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer’s Disease and Related Disorders Association criteria for probable and possible Alzheimer’s disease (McKhann et al., 1984)...Twins and their twin partners underwent identical diagnostic procedures. If the partners were deceased, their diagnosis before death was determined through informant interviews and review of medical records, including death certificates. Cases and partners were followed longitudinally every 18 months.
Case ascertainment from the OCTO-Twin sample was essentially parallel procedurally, entailing a review of MMSE scores and neuropsychological testing, with the cognitive battery parallel to that used in the Study of Dementia in Swedish Twins. For those suspected of dementia, the same informant protocol was followed, medical records were reviewed, and a consensus diagnosis was assigned by a physician and a psychologist."
Covariates & Analysis Detail
Conditional logistic regression
The conditional logistic regression analysis uses only discordant pairs (i.e., twins who have different levels of leisure activity). Discordance is defined as described below.
"For the matched-pairs analyses, each of the factor scores, as well as a summed score of all leisure activities, was dichotomized within pairs by assigning a 1 to twin members with a higher activity score compared with their twin partner and a 0 to the twin member with the lower activity score. When there was a tie in scores, both twins were assigned a 0 because these pairs were uninformative for the analyses."