Table 3.

Details of included studies

Source/ condition	Design	Population/ denominator	Timescale	Case ascertainment method	Diagnostic method	Outcome	Potential bias/methodological limitations
Morrison et al. (1995) [6] HD	Population-based study of prevalence	Northern Ireland population of 1,569,971 based on 1991 national census	Prevalence estimated on April 21, 1991	Northern Ireland GP records; neurologist, psychiatrist and geriatrician records; Department of Medical Genetics diagnostic records	DNA-confirmed diagnoses for all patients	Prevalence of 6.4/100,000	Small founder effect due to large families; however, families not large enough to cause bias in population statistics
James et al. (1994) [7] HD	Population-based study of prevalence	South and Mid Glamorgan, and Gwent; population of 1,393,900 based on 1991 national census	Prevalence estimated on March 1, 1994	HD register for South Wales	Details of formal diagnosis in register; notes of symptom type and onset provided	Prevalence of 6.2/100,000	All known living cases of HD studied; potential for cases not included in register, and subsequent underestimation of prevalence
Watt and Seller (1993) [8] HD	Population-based study of prevalence	Oxford Region Health Authority under NHS; population of 2,520,000	Prevalence estimated on live patients on January 1, 1988	Oxford region medical genetics department records; it is thought by the time of the study all persons affected in 1988 would have been referred and ascertained	Confirmed by presymptomatic linkage test	Prevalence of 4.0/100,000	None identified

HD = Huntington's disease; NHS = National Health Service; GP = general practitioner.