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AlzRisk Paper Detail

Reference: Leibson, 1997
Cohort: Rochester Epidemiology Project
Risk Factor: Diabetes Mellitus

Average Follow-up Time Detail
The average follow-up time pertains only to participants in the diabetes group, for whom the authors provided the total number of participants as well as the person-years of follow-up. Although the number of person-years for the non-diabetic group (the standard population) is estimable using the reported rates for this group, the number of individuals in this group was not provided."

Exposure Detail
"The diagnostic criteria for diabetes mellitus were those outlined by the National Diabetes Data Group (26). The criteria consisted of two consecutive fasting glucose levels >140 mg/dl or 1- and 2-hour levels >200 mg/dl obtained during a standard oral glucose tolerance test. These levels were based on the Auto-Analyzer (Technicon, New York, New York) ferrocyanide reductase technique for plasma, the method used at the Mayo Clinic since May 1972. Glucose values obtained at other institutions or using earlier laboratory methods were transformed to their post-May 1972 equivalents. Persons who failed to meet the criteria above but for whom there was evidence of oral agents or insulin use for at least 2 weeks or until death also qualified as cases.

"Date of diagnosis was the earliest date for which criteria were met. Persons who moved to Rochester with confirmed AODM were assigned the first mentioned date of diagnosis obtained from patient history."

Ethnicity Detail
Not reported in this paper. All participants were residents of Rochester, Minnesota, USA.
According to a description of the cohort, in 1990, 96% of the Olmsted County population were white, many of northern European origin.

Age Detail
Rates were computed within age groups. The minimum age of the youngest age group was 45, and the maximum age of the oldest age group was 99.

Screening and Diagnosis Detail
AD Diagnosis:
DSM IIIR Diagnostic and Statistical Manual III-Revised

"Other" diagnostic criteria: medical record review using DSM-IIIR-like criteria adapted for retrospective review.

Total dementia definition: From medical record review using DSM-IIIR-like criteria adapted for retrospective review.

"The complete medical records of each member of the AODM cohort were reviewed by a nurse abstractor (V. A. H.) and evaluated by a neurologist (E. K.) for evidence of dementing illness. Diagnostic criteria for dementia were based on the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (27), adapted for retrospective record review (figure 1). Based on all available clinical, laboratory, and autopsy information, year of onset of symptoms was assigned and cases were classified as Alzheimer's or non- Alzheimer's disease (figure 1). Cases were classified as Alzheimer's disease combined with other types of dementia including cerebrovascular dementia if 1) there was evidence of both Alzheimer's and non-Alzheimer's disease at autopsy, or 2) if the dementia was characterized by insidious onset and slow progression but was accompanied by preexisting conditions (e.g., stroke, Parkinson's disease, alcoholism) that may have contributed to the dementia. The personnel and the criteria used in this study were the same as those in previous Rochester Epidemiology Project studies describing the incidence and prevalence of dementia and Alzheimer's disease for the Rochester, Minnesota, community (4, 28-32)."

Covariates & Analysis Detail
Analysis Type:
Standardized morbidity ratios (SMRs)

The authors also estimated incidence rate ratios (IRRs) using Poisson regression. For AD, they reported separate diabetes-related IRRs for men and women, adjusting for age, age-squared, age-cubed and calendar year. The diabetes-related IRR for men was 2.27 (95% CI 1.55-3.31), and for women, it was 1.37 (0.94-2.01). The Poisson regression model for TD included terms for age, age-squared and age-cubed, and the results from this analysis indicated a DM-related IRR of 1.66 (95% CI 1.35-2.04).

In addition, the report provided the sample size only for the diabetes cohort (N=1455). Based on data in Table 2, about 4.3%-4.5% of person-years were contributed by the diabetes cohort. Assuming that this distribution roughly applies to the number of people studied, we estimated the total population to be about 33,000.

AD Covariates:

TD Covariates:

The authors adjusted for age (in 5-year age groups) and sex by stratifying on these variables in the calculation of the SMR.