Sunday, January 14, 2007

Prevalence of Personality Disorders

I don't understand how people could think that you estimate the prevalence of personality disorders by statistical studies of patients receiving treatment in mental health clinics.

Passing that off as a legitimate estimate is ridiculous. You can't estimate prevalence that way. You have to take a random sample of the population.

ESPECIALLY for disorders like Narcissistic Personality Disorder and Antisocial Personality Disorder, in which the mentally ill person firmly believes there is nothing wrong with him or her.

One might as well think to estimate the rate of mental illness by hanging out a shingle that says, "Wanted: Everyone Who Thinks They're Sick in the Head."

Did anyone seriously think narcissists and psychopaths are going to answer the call? Mainly only the psychopaths who end up in jail for violent crimes get diagnosed and treated.

The first legitimate survey was taken in 2004, and it doubled DSM estimate of 6-9%, estimating that 15% of American have at least one of seven personality disorders - not counting borderline, schizotypal, and narcissistic disorders. Yikes, imagine the percentage if you add them in.

Since Grant conducted the study among a randomly selected population-based sample, the prevalence rates from her study diverged from those presented in the DSM-IV-TR in some cases.

For instance, according to the DSM-IV-TR, dependent personality disorder is "among the most frequently reported personality disorders encountered in mental health clinics," the study report pointed out. However, Grant's study found it to be the least common in the population.

In addition, the DSM-IV-TR estimates that the prevalence of avoidant personality disorder in the general population is between 0.5 percent and 1 percent, yet Grant found it to be 2.36 percent.

Grant explained that prevalence estimates of various personality disorders in the DSM are based on relatively small, clinical studies of patients who are receiving mental health services on an inpatient or outpatient basis.

"You can run into problems if you rely solely on clinical samples," she said. "If you want to know the true prevalence of a certain disorder, you have to get out of the clinic."

Duh, like how embarrassing to have to state the obvious like that.

Chances are the instrument (questionnaire) needs improvement, but at least this is a start in the direction of real science. The DSM estimates are worthless.
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