Scleritis is not a common disease, although the exact prevalence and incidence are unknown.

It is reported frequently in the Dominican Republic, but exact prevalence there is not known.

The exact prevalence of this condition remains to be established.

The exact prevalence of antiphospholipid syndrome is not well known, as different studies employ different definitions of the condition.

The exact prevalence of food allergy in cats remains unknown.

Episcleritis is a rare disease, and its exact prevalence and incidence are unknown.

The prevalence is widely quoted to be 1/20,000, but the exact prevalence is not known.

The exact prevalence of the syndrome is unknown.

Because Cowden syndrome can be difficult to diagnose, the exact prevalence is unknown; however, it probably occurs in at least 1 in 200,000 people.

Despite extensive research, the exact prevalence of hyperlipidaemia has not been determined due to methodological differences.