Table 6.

Excluded studies

	Disease	Reason for exclusion
Craig et al. (2005) [10]	Dominantly inherited ataxias	Incomprehensive case ascertainment: investigation of a cohort of families with undiagnosed ataxias and suspected Huntington's disease; there may be additional cases outside the cohort studied, hence incomplete case ascertainment
Craig et al. (2004) [11]	Dominantly inherited ataxias	Incomprehensive case ascertainment: investigation of already clinically affected families; no broader searches, therefore possibility of further cases in families not studied, hence incomplete case ascertainment possible
Schrag et al. (1999) [12]	Multiple system atrophy/progressive supranuclear palsy	Incomprehensive case ascertainment: 33/202 patients (16%) identified as potential progressive supranuclear palsy/multiple system atrophy patients declined to be assessed further, therefore complete case ascertainment was not possible; estimates of incidence/prevalence are likely to be too low
Simpson and Johnston (1989) [13]	Huntington's disease	Although study published after 1988, data refer to pre-1988 incidence and prevalence