Inspired by this post on Neuroskeptic’s blog on the rates of personality disorders (PDs) in the UK, I decided to look up some stats on PDs in the US. The most comprehensive survey of the prevalence of PDs in this country to date is the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) undertaken by Grant and colleagues. This was a pretty impressive survey of mental health problems in the general population consisting of approx. 40,000 respondents carried out not once, but twice – of the same subjects, with a 2 – 3 year interval!
When results of the first part of the survey or Wave 1 initially came out, the sheer prevalence of PDs appeared somewhat surprising (link here with a nice bar graph of all the PDs they assessed) as apparently 30.8 million (or 14.8%) in the US population had at least one personality disorder. Additionally, the authors had left out three PDs out of Wave 1 (borderline, schizotypal, and narcissistic) due to difficulties in assessment. However, they did manage to assess these in the second wave conducted about 2 – 3 years later, and when these were added to the estimates, a more recent study by Trull et al. (2010) found that the overall prevalence of PDs shot up even more to 21.5%.
This latter study also tried to clear up the mystery of high PD rates by tightening up the criteria for distress/impairment used in the NESARC survey. The original authors (Grant et al) required that distress/impairment be associated with only one criterion for each PD for a diagnosis. The revised estimates by Trull et al (2010) required every criterion for every PD to be associated with impairment. Naturally, this made it harder to be diagnosed with any PD, and the prevalence of PDs dropped quite drastically from 21.5% to 9.1%. However, according to Trull et al, it also brought it more in line with other previous surveys of PDs to date. So, we can already see glimmers of some problems with PD rates calculated by NESARC so far.
Additionally, when wading through these articles what caught my eye was this paper from the NESARC group. Keep in mind that some PDs were assessed only in Wave 1, while others were assessed only in Wave 2.
So:
Wave 1: Paranoid, Schizoid, Antisocial, Histrionic, Narcissistic, Avoidant, Dependent, Obsessive-Compulsive
Wave 2: Schizotypal, Borderline, Narcissistic
This paper on correlates of borderline PD states in its abstract that, “With additional comorbidity controlled, associations with bipolar disorder and schizotypal and narcissistic PDs remained strong and significant”. That made me pause a few seconds.
So, in other words, even after taking out the effects of all other co-occurring Axis I and II disorders, the three PDs that were specifically assessed only in Wave 2 had some sort of special relationship….? That seems like quite a coincidence to me.
The authors don’t discuss the possibility that this might actually be an artifact of assessment at all and seem to consider this a “true” finding. In fact, if their tables are anything to go by, their results indicate that a whole bunch of people developed these three specific PDs between Wave 1 and Wave 2, or alternatively, that their survey is not working quite as well as they think.
Here’s a condensed version of these findings from the paper (Table 4 from their paper – I’ve cut down quite a few columns and rows to make it easier to read) that details the odds ratios of associations between borderline PD and any other disorder after controlling for associations with all other remaining disorders (both Axis I and II) and sociodemographic characteristics.
And you can immediately see that the odds ratios between borderline PD, and schizotypal and narcissistic PDs (those assessed only in Wave 2) far exceed those of all the other PDs (these were assessed only in Wave 1). The only other disorders that come close are bipolar I and II. I’ll leave you to draw your own conclusions.
This paper has been cited quite a few times (89 according to Google) since it was published, and a quick skim of the citing articles suggested that no one had really questioned the validity of these estimates (though it is very possible that I could have missed something).
Clearly, a survey like NESARC is an impressive undertaking – face to face standardized interviews of 40,000 people carefully selected to be representative of the population, and re-interviewed in 3 years is no small achievement. However, data for the sake of data, without a deeper investigation of what the numbers mean is not really useful, and worse, can be potentially misleading.
Grant BF, Stinson FS, Dawson DA, Chou SP, Ruan WJ, & Pickering RP (2004). Co-occurrence of 12-month alcohol and drug use disorders and personality disorders in the United States: results from the National Epidemiologic Survey on Alcohol and Related Conditions. Archives of general psychiatry, 61 (4), 361-8 PMID: 15066894
Grant BF, Chou SP, Goldstein RB, Huang B, Stinson FS, Saha TD, Smith SM, Dawson DA, Pulay AJ, Pickering RP, & Ruan WJ (2008). Prevalence, correlates, disability, and comorbidity of DSM-IV borderline personality disorder: results from the Wave 2 National Epidemiologic Survey on Alcohol and Related Conditions. The Journal of clinical psychiatry, 69 (4), 533-45 PMID: 18426259
Trull TJ, Jahng S, Tomko RL, Wood PK, & Sher KJ (2010). Revised NESARC personality disorder diagnoses: gender, prevalence, and comorbidity with substance dependence disorders. Journal of personality disorders, 24 (4), 412-26 PMID: 20695803
Mmm, well spotted. This is indeed something that could be an artefact of assessment. It wouldn't even have to be anything very complicated. For almost anything, if you ask a bunch of questions on one day, then wait a while, and ask a second bunch, within-bunch correlations are going to be stronger relative to between-bunch, just because various random things will have happened in the intervening time which may change the results.
ReplyDeleteFor example if you wanted to correlate blood pressure to salt intake, and then, 10 years later, asked them about their weight, you would probably find that salt is more important than weight as a correlation of blood pressure even if, in fact, it's the opposite.
I am surprised this kind of stuff got through peer review. It's also a little hard for me to believe that Grant and colleagues somehow missed this fact when running their analyses and writing up this paper. Mistakes happen, and obviously no one wants to point out potential flaws in their own work. But you would think there's a higher degree of responsibility and accounting involved when you are trying to get precise estimates of rates of mental disorders for an entire country.
ReplyDeleteHi there, would you like to take an Avoidant personality disorder test?
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