Prevalence and Incidence of Factor XI deficiency, congenital
Ophanet, who are a consortium of European partners,
currently defines a condition rare when if affects 1 person per 2,000.
They list Factor XI deficiency, congenital as a "rare disease".
More information about Factor XI deficiency, congenital is available from Orphanet
About prevalence and incidence statistics:
The term 'prevalence' of Factor XI deficiency, congenital usually refers to the estimated population
of people who are managing Factor XI deficiency, congenital at any given time.
The term 'incidence' of Factor XI deficiency, congenital refers to the annual diagnosis rate,
or the number of new cases of Factor XI deficiency, congenital diagnosed each year.
Hence, these two statistics types can differ:
a short-lived disease like flu can have high annual incidence but low prevalence,
but a life-long disease like diabetes has a low annual incidence but high prevalence.
For more information see about prevalence and incidence statistics.