Methodological Factors in Determining Rates of Dementia in Transient Ischemic Attack and Stroke
(I) Impact of Baseline Selection Bias
Background and Purpose—Many previous studies on dementia in stroke have restrictive inclusion criteria, which may result in underestimation of dementia rates. We undertook a large prospective population-based study of all transient ischemic attack and stroke to determine the impact of study entry criteria on measured rates of pre- and postevent dementia.
Methods—All patients with acute transient ischemic attack or stroke from a defined population of 92 728 are referred from primary care or at hospital admission to the Oxford Vascular Study (2002–2007) and have baseline clinical and cognitive assessment and follow-up. We examined the impact of early death, other nonavailability, and commonly used selection criteria, on measured rates of dementia.
Results—Among 1236 patients (mean age/SD 75.2/12.1 years, 582 men, 403 transient ischemic attack), 139 died or were otherwise unavailable for baseline assessment, 319 had prior dependency, 425 had comorbidity, 512 were aged ≥80 years, 85 were dysphasic, and 502 were hospitalized. Pre-event dementia was 3-fold higher in patients dying preascertainment (10/47, 21%) and twice as high in other nonassessed (14/92, 15%) versus assessed patients (69/1097, 6%; P=0.0006 and P=0.002) and was several-fold higher in those with prior functional impairment (24% versus 3%; P<0.0001), age >80 years (13% versus 3%; P<0.0001), dysphasia (11% versus 7%; P<0.0001), and comorbidity (10% versus 6%; P=0.04). Findings for postevent dementia were similar: prior functional impairment (40% versus 13%; P<0.0001), age >80 years (28% versus 10%; P<0.0001), dysphasia (39% versus 15%; P<0.0001), and comorbidity (20% versus 15%; P=0.04).
Conclusions—Exclusion of patients unavailable for assessment, and other widely used selection criteria, results in underestimation of the measured rate of dementia associated with transient ischemic attack and stroke.
- Received November 5, 2014.
- Revision received December 19, 2014.
- Accepted January 7, 2015.
- © 2015 American Heart Association, Inc.