title: Methodological factors in determining rates of dementia in transient ischemic attack and stroke: (I) impact of baseline selection bias.
abstract: OBJECTIVE
  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.
authors: From the Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.); and University of Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.). sarah.pendlebury@ndcn.ox.ac.uk.
authors: Sarah T
authors: ST
authors: Pendlebury
authors: From the Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.); and University of Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.).
authors: Ping-Jen
authors: PJ
authors: Chen
authors: From the Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.); and University of Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.).
authors: Linda
authors: L
authors: Bull
authors: From the Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.); and University of Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.).
authors: Louise
authors: L
authors: Silver
authors: From the Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.); and University of Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.).
authors: Ziyah
authors: Z
authors: Mehta
authors: From the Stroke Prevention Research Unit, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.); and University of Oxford, United Kingdom (S.T.P., P.-J.C., L.B., L.S., Z.M., P.M.R.).
authors: Peter M
authors: PM
authors: Rothwell
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003704:Dementia / Q000150:complications* / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006760:Hospitalization; D006801:Humans; D002546:Ischemic Attack, Transient / Q000150:complications* / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D011446:Prospective Studies; D012107:Research Design; D015983:Selection Bias; D020521:Stroke / Q000150:complications* / Q000453:epidemiology*; D016896:Treatment Outcome
keywords: dementia; ischemic attack, transient; selection bias; stroke
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