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Try out PMC Labs and tell us what you think. Learn More. Though archival literature states that schizophrenia occurs equally in males and females, recent epidemiological studies report higher incidence of schizophrenia in men than women. Moreover, there is longstanding evidence that women may be under-represented in non-epidemiological research literature.
Our first goal was to quantify gender ratios in non-epidemiological research published in Secondly, we sought to investigate which factors contribute to high s of men in research studies. Our final goal was to compare gender ratios in non-epidemiological schizophrenia research to reported incidence rates. In a recent meta-analysis of incidence, there were 1. In non-epidemiological studies of the schizophrenia patients, there was an average of 1. Although the degree to which men outed women varied according to study type and region of study, research studies included more men than women across all investigated variables.
Either the incidence rates are higher for men than has ly been reported or women are less visible in research settings than in the greater community. Importantly, the discrepancy between gender ratios in epidemiological and non-epidemiological research is consistent. However, specific, identifiable factors are present when male participants are greatest, suggesting that many research environments yield a higher of men.
Thus much of our understanding of the illness and its treatment is based on research conducted disproportionately with men. Recent epidemiological literature has shown unequal incidence of schizophrenia for men and women. This is not clearly the result of a systematic bias in diagnostic systems. Rather, it appears that more males get ill. Younger male onset is one of the explanations evoked for higher male incidence Hafner et al.
In earlier studies that relied on the third edition of the Diagnostic and Statistical Manual of Mental Disorders DSM-III; American Psychiatric Association,this could certainly be true since women who developed schizophrenia after age 45 were excluded and thus incidence - the of new cases per year - of schizophrenia was biased towards men.
However, this disparity seems to be exaggerated in the non-epidemiological research literature e. Thus, although epidemiological and non-epidemiological research show greater proportions of men than women, this disproportion has become more pronounced in non-epidemiological research. To update this research and to investigate possible moderators of the effect, we analyzed the s of men and women with schizophrenia appearing in various research studies.
Furthermore, as publications considered epidemiological and non-epidemiological research independently, we tested for statistical differences between these two literatures. We hypothesized that there would be fewer females in non-epidemiological schizophrenia research than expected from incidence rates. If true, this would suggest that the non-epidemiological literature is weighted toward male patients and may not generalize fully to female patients. As our baseline for comparison, we chose the incidence rate of 1.
We used this incidence value rather than estimated prevalence i. A review was conducted of all non-epidemiological research articles published on schizophrenia in in the following seven high impact psychiatric journals: Archives of General Psychiatry, American Journal of Psychiatry, British Journal of Psychiatry, Biological Psychiatry, Molecular Psychiatry, Schizophrenia Research, and Schizophrenia Bulletin.
Authors J. Where the necessary values were vaguely or incompletely stated, they were resolved through consultation. Of articles published in those journals inwere reviews, editorials, case studies, did not investigate schizophrenia patients, or did not indicate the of male or female patients.
Of remaining articles, thirty-five studies of postmortem patients, Veterans Administration facilities military hospitalsor single gender were excluded. Ten studies appeared to involve samples that overlapped with other studies. Lastly, we required that included studies use relatively common diagnostic criteria i. DSM-III-R or more recent; ICD 8 or more recentreport data on schizophrenia independently from general psychosis, and not only consider subtypes of the schizophrenia spectrum; 28 studies did not meet these inclusions criterion. After exclusions, articles referenced in Appendix 1 were analyzed.
The proportion of male participants, calculated as males divided by participants male plus femalewas used in our analysis. We coded the non-epidemiological articles according to seven multi-level categorical variables. The journals investigated are listed above; 2. Study types were a functional neuroimaging fMRI, MEG, PET, EEGb anatomical using imaging techniques to assess brain structure or chemistryc cognitive examining performance on cognitive tasksd genetic reporting of various genetic and familial liability analysese psychosocial assessing psychosocial interventions, symptoms, and diagnostic criteriaand f pharmacological assessing different pharmacological manipulations ; 3.
The illness stages were a prodromal, b first-episode, c first-admission, and d lifetime; 5. Geographical breakdown was by continent and included: a North America, b Europe, c Asia, d Australia, Where have all the older woment gone e multiple sites; 6. Diagnoses were a schizophrenia only, b schizophrenia or schizoaffective disorder, and c schizophrenia spectrum.
Additionally, two continuous variables, namely the mean age of participants, and the sample size were collected. We attempted to analyze refusal rates and information on the diagnostic process, but there were insufficient data.
Current research has many Where have all the older woment gone of meta-analysis. However, our focus is not the experimental endpoint of a group of studies but, rather, a statistics that is possibly ancillary i. Therefore, the assumptions underlying typical meta-analysis are not met Hunter, In place of standard meta-analyses, we took the following straightforward statistical approach. The first set of analyses considered only the non-epidemiological data. Regression coefficients determined whether the age of participants or sample size affected the proportion of male participants.
Second, we compared the non-epidemiological data to the expected gender proportions, as defined by McGrathin t-tests for single means. We checked for normality for the distributions of all the proportions, and found no meaningful departure. We also applied the standard arc-sine transformation to the proportions and found no meaningful differences between those inferences and those obtained using just the t-test.
Moreover we checked the analysis using chi square tests of equality and found no departure from the t-test. The central fact of the proportions data is that virtually all are approximately centered in the interval [0. The articles from the non-epidemiological research literature includedmales andfemales. We analyzed articles from Schizophrenia Bulletin and Schizophrenia Research separately from the other five journals in order to rule out the possibility that gender ratios in articles published in journals focusing specifically on schizophrenia might be unrepresentative.
However, there were no differences in effect or levels of ificance. In order to directly compare our findings to reports 13, 14we separately considered the articles from the Archives of General Psychiatry. We examined whether the difference between epidemiological and non-epidemiological literature was ificant. The remaining analyses investigated the seven multi-level categorical variables identified in Methods. Table 2 summarizes findings for the first five of these variables. As seen in the table, there were numerical differences of male participants exceeded that of females in every journal, in every study type, in every type of sample, institution, and continent.
Critically, in most cases, the male proportion in the non-epidemiological studies ificantly exceeded the imbalance that would have been expected based on the baseline incidence value taken from the epidemiological literature. Indeed, 19 of the 25 post hoc t-test comparisons were ificant, even after control for multiple comparisons, suggesting a clear and consistent excess of males in non-epidemiological research relative to the value expected based on epidemiological findings.
Non-epidemiological research findings by individual variable levels. This is also indicated by the asterisks and bold font. Though the majority of comparisons favored our hypothesis, there were exceptions, as follows. The category of genetic articles did not yield a ificant result. This group of studies was consistent with the proportion of 0. In addition, gender proportions for articles that investigated pharmacological topics, were published in Molecular Psychiatry, looked at converted cases in prodromal samples, or were conducted in Asia, Australia or in multiple locations did not differ ificantly from incidence estimates.
Note that in nearly all of these cases where ificance was not maintained following correction, males still exceeded females numerically. Diagnosis variable 7 in Methods did not affect the proportion male. In fact, though the differences were not ificant, those studies including schizophrenia spectrum diagnoses yielded the most female participants. We then considered the effect of the remaining variables. The of participants did not correlate to the proportion of males. Our analysis revealed a widespread mismatch between the incidence of schizophrenia in females and their participation in research studies.
Additional points emerge from the examination of moderators of this effect. There was some variability in gender proportions as a function of study characteristics, but all variables contained numerically more males than females and, for most, these differences were ificant compared with the epidemiological literature, and survived statistical corrections for multiple testing. Our estimate of the magnitude of this effect may be conservative. Had we used the prevalence values that appear in the literature i.
Thus, the evidence against equal frequency of the disorder across gender is strong in the epidemiological research — however, this imbalance is ificantly exaggerated in published non-epidemiological research studies. In the 's, gender proportions in epidemiological and non-epidemiological seemed to be matched. However, the 's saw large jumps in the of male research participants. Our findings are comparable to those of the 's.
Thus, males appear to have remained overrepresented in the literature for over two decades. We found a ificant correlation of age and the gender of participants, with fewer males the older the mean age of the sample. When comparing the of participants to their gender, it made sense that larger samples might liken the gender proportions of non-epidemiological research to epidemiological findings.
Yet, the regression was not ificant, suggesting that the nature of the research, more than the size of the sample, influenced the of females. Since the proportion of males was ificantly greater than the epidemiological baseline for nearly all the categorical variables, the elevated of males in non-epidemiological research does not appear to be an isolated occurrence. The few studies that resemble the incidence rate- namely genetic, Molecular Psychiatry, prodromal, Asian, Australian, and transcontinental studies- offer Where have all the older woment gone into characteristics that increase the of females in patient samples.
There was a trend level effect for diagnostic system but, given the unbalanced subgroups, this possible effect requires further investigation. Unexpectedly, the type of diagnosis e.
Explaining the considerable difference between the incidence literature and the non-epidemiological literature is difficult. First, it is possible that the incidence of schizophrenia in women is overestimated. Other studies find that gender does not predict diagnosis accuracy Moilanen et al. However, the fact Where have all the older woment gone the prodromal conversion literature approximates the epidemiological literature weakens this explanation.
Another explanation is that a greater proportion of female patients in hospitals and clinics choose not to participate in research. However, there was not sufficient information in our data to address this point. Future studies would benefit from considering the relationship of gender and variables during recruitment, such as refusal rates.
It may be that many women with schizophrenia never enter the treatment settings where most clinical research is conducted. Our findings are most consistent with this hypothesis. The prodromal patients matched the epidemiological ratio, while chronic and first episode populations contained a far higher of men. Of note, the recruitment of prodromal patients typically involves very aggressive case finding methods, often outside of mental health treatment settings, methods more akin to those typically employed in epidemiological and genetic research.
This suggests that only some portion of cases present for care in the settings captured in the first episode literature, and that portion is comprised very largely of male patients. It is possible that there are substantial s of female patients with schizophrenia who remain fully outside of the clinical settings where schizophrenia research is conducted. Thus gender differences may not be pronounced affecting study participation and trajectory of illness until after the prodromal stage. Careful screening during the recruitment process, as in genetic studies that employ large, representative populations, seems to result in gender ratios similar to epidemiological predictions.
This may explain why gender proportions in studies reported in Molecular Psychiatry, publishing with a heavy emphasis on genetic research, more nearly approximates actual incidence proportions. Since the degree of unevenness varied according to continent of study, we must also consider the impact of culture, economy, and human participant protection practices. Stringent ethical guidelines can make it more difficult to recruit female participants, particularly those of childbearing years.
In an effort to understand the gender discrepancy, we separately examined a of broad and obvious differences across studies that might moderate the effect, including journal of publication, study type, sample, institution, continent, and diagnostic criteria.Where have all the older woment gone
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