Table 3.

Cohort studies: Newcastle-Ottawa Scale for assessment of quality of included cohort studies

	Acceptable criteria	Petkus et al21		Gallacher et al20
Selection
Representativeness of exposed cohort	Representative of average adult in the community (age(s), BMI, BP, CAMDEX, CDR, DSM III/IV/V, FAB, GHQ-30, ICD-10, MMSE, NR, STAI)	Population-based Swedish twin registry, subsample of twins aged ≥50 years	+	Men only, representative of male inhabitants of Caerphilly region	−
Selection of non-exposed cohort	Drawn from same community as exposed cohort	Drawn from same community as exposed cohort	+	Drawn from same community as exposed cohort	+
Ascertainment of exposure	Secured records, clinical diagnosis using diagnostic tools (ICD-10/DSM-V)	State anxiety subscale of STPI, containing a subset of items from the STAI	+	Structured interview using STAI	+
Demonstration that outcome of interest was not present at start of study	Assessment for dementia at initial enrolment	No baseline screening, exclusion if previous dementia diagnosis, age at inclusion (mean age 60.86 years) makes cognitive impairment unlikely	−	Age at inclusion (mean age 56.1 years) makes cognitive impairment unlikely	−
Comparability
Comparability of cohorts on basis of design or analysis	Study controls for the most important factor (+/-) and for any additional factor (+/-)	Multivariate models control for depression symptoms, baseline age, sex, education, physical illness	++	Study controls for age, social class, marital status, vascular risk factors (alcohol consumption, BP, BMI, total cholesterol, previous vascular disease), educational ability (National Adult Reading Test) and depression symptoms (GHQ-30)	++
Exposure
Assessment of outcome	Independent blind assessment, record linkage	Screening for dementia using MMSE, cognitive in-person testing (assessing a range of cognitive domains), DSM-III or IV and record linkage using National Patient Registry and National Patient Cause of Death Registry	+	Cognitive function assessed using CAMDEX, FAB, CDR; diagnosis made using DSM-IV, screening of primary care and hospital records	+
Follow-up adequate for outcome to occur	Follow-up >10 years	28 years	+	>20 years	+
Adequacy of follow-up of cohorts	Complete follow-up or subjects lost to follow-up unlikely to introduce bias	NR	−	20% lost to follow-up	+
Total score			7		7

+/− represents whether individual criterion within the subsection was fulfilled, two symbols indicate that two criteria were assessed within the subsection.

BMI, body mass index; BP, blood pressure; CAMDEX, Cambridge Mental Disorders of the Elderly Examination; CDR, Clinical Dementia Rating; DSM III/IV/V, Diagnostic and Statistical Manual of Mental Disorders III/IV/V; FAB, Frontal Assessment Battery; GHQ-30, 30-item General Health Questionnaire; ICD-10, International Classification of Diseases 10th Revision; MMSE, Mini-Mental State Examination; NR, not recorded; STAI, State Trait Anxiety Inventory; STPI, State Trait Personality Inventory.