These results should be interpreted in light of several limitations. The response rate was only 70%. As described in more detail elsewhere,15
we assessed this problem in a non-respondent survey where a sub-sample of initial non-respondents was offered a large financial incentive ($100) to complete a short (15-minute) telephone interview that included CIDI diagnostic stem questions. No significant difference was found in panic stem question endorsement compared to the main survey sample, indirectly arguing against large non-response bias on the basis of panic. Second, although good concordance with SCID PD diagnoses was found, no validity data were obtained for PA or AG. Third, information about AOO, persistence, and other important course and treatment variables were obtained retrospectively that could be biased. As described in more detail elsewhere,16
a number of strategies were used in the NCS-R to reduce recall bias. Evidence exists that these strategies improved accuracy of retrospective AOO reports,30
but we have no data about effects on other aspects of recall.
With these limitations as a backdrop, the NCS-R lifetime prevalence estimates of DSM-IV PD and PD-AG (4.7%, 1.1%) are similar to the DSM-III-R estimates in the baseline NCS (3.5%, 1.5%). The NCS-R estimate of PD-only prevalence (3.7%) is substantially higher than in the NCS (2.0%).2
Although higher than in earlier epidemiological surveys,31
the concordance of the NCS-R PD prevalence estimate with an independent SCID estimate argues against upward bias. In the case of AG, the concern is more with downward than upward bias based on the fact that the CIDI requirement of anxiety about multiple situations is stricter than the DSM-IV requirement.
Estimates of persistence, socio-demographic correlates, and psychiatric comorbidity are broadly consistent with the baseline NCS1, 2, 32
and other previous epidemiological surveys,14, 31, 33–35
although direct comparison is not possible because previous surveys did not disaggregate panic into the four subgroups considered here. High prevalence among women, low prevalence among the elderly, and strong comorbidity with other anxiety and mood disorders are all noteworthy consistencies with previous surveys. One notable difference is a much higher estimated lifetime prevalence of panic attacks in the NCS-R (28.3%) than the NCS (7.3%), a discrepancy presumably due to the more detailed stem questions in the DSM-IV version of the CIDI than in the DSM-III-R version that suggests panic attacks were underestimated in the baseline NCS.
We are aware of no previous general population research that compared the prevalence and correlates of isolated panic attacks versus panic disorder with and without agoraphobia. The most striking results of this comparison are that isolated panic attacks are both quite common and significantly comorbid with other DSM-IV disorders. These results are consistent with clinical studies.36, 37
The vast majority of people with isolated panic attacks fail to meet PD criteria because they never had recurrent uncued attacks, although they typically had numerous cued attacks. Another notable subgroup results is that cued attacks are more common than uncued attacks even among people with PD. This is especially striking given that probing often uncovers initially unrecognized panic cues,38, 39
which means that the NCS-R probably underestimates the proportion of attacks that are cued. We also found that persistence and number of lifetime attacks are more strongly related to PD than AG, that comorbidity, especially with other anxiety disorders, is more strongly related to AG than PD, and that isolated panic attacks are associated with substantial role impairment when they occur in conjunction with AG.
The subgroup results suggest that AG and PD are to some extent distinct, as about 40% of all respondents with PA and AG never met criteria for PD. This finding is consistent with family aggregation studies, which show that risk of AG is significantly elevated among relatives of people with PA-AG43
and relatives of people with PD-AG compared to PD-only.39,40
Family genetic studies also suggest that AG and PD may have at least some distinct pathogenic mechanisms.41,42
At the same time, our finding of higher conditional prevalence of AG among people with PD than PA is consistent with the strong association between AG and PD long observed in clinical settings.
The subgroup results document monotonic increases from PA-only to PD-AG in number of attacks, comorbidity, clinical severity, role impairment and treatment seeking, with intermediate values for PA-AG and PD-only. Together with the finding that a high proportion of AG is associated with PA, these results could be interpreted as suggesting that panic exists along a continuum in which PA and PD differ in degree rather than in kind. This interpretation is consistent with prior findings that infrequent, spontaneous panic attacks are common in the general population,40, 41
that these attacks typically include fewer and less severe symptoms than those of patients with PD,42
and that infrequent PA aggregates with PD in families.43, 44
The distinction between cued and uncued attacks might be called into question as part of this same line of thinking based on the view that the vast majority of panic attacks are to some extent cued.37, 45, 46
It would be premature to conclude from these results that the boundary between PA and PD is arbitrary. Nevertheless, given the high prevalence of PA-only and the negative outcomes associated with PA-only, future research might profitably attempt to subset PA-only and evaluate whether diagnostic criteria or symptom thresholds for panic disorder should be modified to improve differentiation between pathological and normal panic experiences.
An innovation of the NCS-R was the use of a fully structured version of the PDSS to assess clinical severity. Although lower than in clinical samples, close to 90% of respondents with PD-AG and roughly 50% of those with PA-AG and PD-only were found to be in the clinically significant range on the PDSS. A related finding is that both clinical severity assessed in the PDSS and role impairment assessed in the SDS appear to be influenced nearly as much by agoraphobia (PA-AG vs. PA-only) as panic disorder (PD-only vs. PA-only). This is consistent with prior findings that AG is associated with panic severity, anticipatory anxiety, and cognitive correlates of severity40, 47–49
and our finding that AG is more common among people with PD than PA. Also consistent with this pattern is the higher average number of lifetime panic attacks among respondents with versus without AG in both the PA and PD samples. One possible interpretation of this pattern is that AG is a severity marker of panic, although this is at least superficially inconsistent with the notion in the last paragraph that AG is distinct from PD disorder. Another possibility is that AG has a direct effect on impairment.
The treatment results are consistent with previous NCS-R reports that most people with PD eventually obtain treatment,23
that most active cases receive treatment in a given year,50
and that most current treatment (45–60% across the three PD and-or AG subgroups) fails to meet basic treatment guidelines.50
The latter result is all the more striking in that our definition of treatment quality is liberal. For example, no distinction was made among psychotherapies despite much more evidence for the effectiveness of some types of psychotherapy than others in treating panic.51–53
Nor was a distinction made among antidepressants or anxiolytics despite much more evidence for the effectiveness of some than others.54, 55
In interpreting the finding that many patients fail to receive guideline-concordant treatment, it should be recognized that some patients were so classified because they dropped out of treatment prematurely rather than because treatment providers delivered inappropriate care. Both problems need to be addressed in future practice-oriented research.