I was asked again about the incidence and prevalence of mental health problems in deaf people. I've never seen a good answer, so this is mine:

I've seen data that says the incidence (number of new cases per year) and prevalence (number of cases) of mental health problems are the same for deaf and hearing people, and I've seen data saying deaf people suffer from twice as many.
However, you need to define both "deaf" and "mental health problem" before you present such statistics and nobody ever convincingly has, that I know of.

• Slightly deafened in old age
• Prelingually profoundly deaf
• BSL user
• Unilaterally deaf
• Fidelity problems
•  ... etc

"Mental Health Problems" means:

• Paranoid schizophrenia
• Alcoholic
• Aspergers Syndrome
• Arachnophobia
• Depression for apparently no reason
• Depression for a very good reason
•  ... etc

It is probable that there is a higher incidence because various mental health problems can be caused and/or maintained by THE CAUSE OF DEAFNESS. So you might be deaf from meningitis or a head injury and those things can give rise to all sorts of 'mental' difficulties. Equally the EFFECTS of deafness can cause or exacerbate - such as unemployment, identity problems, exploitation etc. The prevalence may well be higher because deaf people do not tend to seek help, because of lack of education about problems and services, and because of lack of faith in the services that exist (like being able to understand the GP, who may not book an interpreter, and whose receptionist may well just call your name at the appointment time.) Also because psychological therapy is essentially based upon communication ("talking therapies"), there is the whole issue of BSL-English, interpreters, triadic therapy, etc...

So it depends what you mean by the question.