The terms "competence" and "incompetence" refer to a person's ability to understand the nature and consequences of decisions and should be restricted to describe a person's legal status.
A person may be declared incompetent in business or financial matters but remain legally competent to consent or refuse care.

Competence is determined by a proper legal authority, usually a judge.

Jaffe E and Knight CF. Unipac six: ethical and legal dimensions of treating life-limiting illness. Hospice and palliative care training for physicians: a self-study program. American Academy of Hospice and Palliative Medicine. 3rd ed. 2008. p. 15.

Possession of a satisfactory level of relevant knowledge and acquisition of a range of relevant skills that include interpersonal and technical components necessary to perform the tasks that reflect the scope of professional practices.
It is therefore not the same as “knowing”.
Competence may differ from “performance”, which denotes actions taken in a real life situation - although the integration of understandings, abilities and professional
judgments can be inferred from performance.

Adapted from Andrzej Wojtczak. Glossary of Medical Education Terms. AMEE Occasional Paper No 3. Internet. Accessed on August 29, 2017.