Club foot is a rare disease due to congenital skeletal abnormalities, both genetic and nongenetic factors are thought to be responsible for club foot. A family in which club foot was inherited as an autosomal dominant trait with reduced penetrance was identified in 2008. It was found that a mutation in the PITXI gene that caused club foot in this family. Through DNA testing, they determined that 11 people in the family carried the PITXI mutation, but only 8 of these people had club foot.

Required:
What is the penetrance of the PIXTI mutation in this family?