Application of Markov chain Monte Carlo methods to modelling birth prevalence of Down syndrome

Data collected before the routine application of prenatal screening are of unique value in estimating the natural live-birth prevalence of Down syndrome. However, much of these data are from births from over 20 years ago and they are of uncertain quality. In particular, they are subject to varying degrees of underascertainment. Published approaches have used ad hoc corrections to deal with this problem or have been restricted to data sets in which ascertainment is assumed to be complete. In this paper we adopt a Bayesian approach to modelling ascertainment and live-birth prevalence. We consider three prior specifications concerning ascertainment and compare predicted maternal-age-specific prevalence under these three different prior specifications. The computations are carried out by using Markov chain Monte Carlo methods in which model parameters and missing data are sampled.     

Estimation of the Force of Infection from Current Status Data Using Generalized Linear Mixed Models

Based on sero-prevalence data of rubella, mumps in the UK and varicella in Belgium, we show how the force of infection, the age-specific rate at which susceptible individuals contract infection, can be estimated using generalized linear mixed models (McCulloch & Searle, 2001). Modelling the dependency of the force of infection on age by penalized splines, which involve fixed and random effects, allows us to use generalized linear mixed models techniques to estimate both the cumulative probability of being infected before a given age and the force of infection. Moreover, these models permit an automatic selection of the smoothing parameter. The smoothness of the estimated force of infection can be influenced by the number of knots and the degree of the penalized spline used. To determine these, a different number of knots and different degrees are used and the results are compared to establish this sensitivity. Simulations with a different number of knots and polynomial spline bases of different degrees suggest - for estimating the force of infection from serological data - the use of a quadratic penalized spline based on about 10 knots.     

Prevalence and Diagnostic Correlates of DSM-IV Pathological Gambling in Psychiatric Outpatients

Studies of the prevalence of pathological gambling (PG) in psychiatric and substance abusing patients suggest that the disorder is not rare. Most studies have been of substance abusers in treatment, and the rate of PG has been found to be several times higher than the rate found in community based epidemiological surveys. However, only one study has examined the prevalence of PG in a heterogeneous sample of patients, and this was a study of psychiatric inpatients. We are not aware of any prior study of the prevalence of PG in a psychiatric outpatient sample. In the present report from the Rhode Island Methods to Improve Diagnosis and Services (MIDAS) project we examined the current and lifetime prevalence of PG in 1,709 psychiatric outpatients interviewed with a semi-structured diagnostic interview that included a module to diagnose DSM-IV PG. Forty (2.3%) patients had a lifetime history of DSM-IV PG, all of whom had at least one other DSM-IV axis I disorder. Patients with PG had significantly more axis I disorders than patients without PG, and had significantly higher rates of bipolar disorder, social phobia, panic disorder with agoraphobia, alcohol use disorder, and other impulse control disorders. Possible reasons for the low prevalence of PG in our sample are discussed.     

Examining Sex Differences in the Use of Direct and Indirect Aggression

Direct and indirect aggressive behaviors were studied using surveys and interviews of students in two public schools. The variables of “sex-of-aggressor” and “sex-of-target” were included. Claims in previous research that girls engage in far more indirect aggression than boys are not supported. Further, it was found that girls are more likely to target the opposite sex with direct aggression than boys. This suggests more gender fluidity in the use of aggression by girls and adds to a growing body of research that dispels the notion that direct and indirect aggression can be neatly sorted into male and female categories of behavior.

Bayesian sample size determination for estimating binomial parameters from data subject to misclassification

We investigate the sample size problem when a binomial parameter is to be estimated, but some degree of misclassification is possible. The problem is especially challenging when the degree to which misclassification occurs is not exactly known. Motivated by a Canadian survey of the prevalence of toxoplasmosis infection in pregnant women, we examine the situation where it is desired that a marginal posterior credible interval for the prevalence of width w has coverage 1−α, using a Bayesian sample size criterion. The degree to which the misclassification probabilities are known a priori can have a very large effect on sample size requirements, and in some cases achieving a coverage of 1−α is impossible, even with an infinite sample size. Therefore, investigators must carefully evaluate the degree to which misclassification can occur when estimating sample size requirements.     

Reflections on Accuracy

The difference between test accuracy and predictive accuracy is presented and defined. The failure to distinguish between these two types of measures is shown to have led to a misguided debate over the interpretation of prevalence estimates. The distinction between test accuracy defined as sensitivity and specificity, and predictive accuracy defined as positive and negative predictive value is shown to reflect the choice of the denominator used to calculate true positive, false positive, false negative, and true negative rates. It is further shown that any instrument will tend to overestimate prevalence in low base rate populations and underestimate it in those populations where prevalence is high. The implications of these observations are then discussed in terms of the need to define diagnostic thresholds that have clinical and policy relevance.     

Estimates of human immunodeficiency virus prevalence and proportion diagnosed based on Bayesian multiparameter synthesis of surveillance data

Summary.  Estimates of the number of prevalent human immunodeficiency virus infections are used in England and Wales to monitor development of the human immunodeficiency virus–acquired immune deficiency syndrome epidemic and for planning purposes. The population is split into risk groups, and estimates of risk group size and of risk group prevalence and diagnosis rates are combined to derive estimates of the number of undiagnosed infections and of the overall number of infected individuals. In traditional approaches, each risk group size, prevalence or diagnosis rate parameter must be informed by just one summary statistic. Yet a rich array of surveillance and other data is available, providing information on parameters and on functions of parameters, and raising the possibility of inconsistency between sources of evidence in some parts of the parameter space. We develop a Bayesian framework for synthesis of surveillance and other information, implemented through Markov chain Monte Carlo methods. The sources of data are found to be inconsistent under their accepted interpretation, but the inconsistencies can be resolved by introducing additional 'bias adjustment' parameters. The best-fitting model incorporates a hierarchical structure to spread information more evenly over the parameter space. We suggest that multiparameter evidence synthesis opens new avenues in epidemiology based on the coherent summary of available data, assessment of consistency and bias modelling.     

Prevalence rate of DSM mental disorders among adolescents living in residential group homes of the French Child Welfare System

Purpose

To determine the prevalence of some major mental disorders among adolescents living in a residential group home and the distribution of these disorders by gender.

Method

The participants included 183 adolescents (13–17 years old) living in residential group homes of the Child Welfare System in the county of Bouches-du-Rhône (South of France). A structured psychiatric Diagnostic Interview Schedule for Children was used to assess the existence of Anxiety Disorder (AD), Major Depression (MD), Conduct Disorder (CD), Eating Disorder (ED), Enuresia (En), Psychosis Screen (PS) and Attention Deficit Hyperactivity Disorder (ADHD) among the study participants over the six-month period before the assessment was taken. The existence of Suicide Attempts (SA) during the lifetime of each child was also assessed.

Results

Of the youths qualified, 48.6% as having at least one psychiatric disorder during the last six months (AD: 28.4%; CD: 15.3%; MD: 14.8%; PS: 18.6%; ADHD: 3.8%), and SA have been reported in 23% of them. Females were more affected than boys (p < 0.001) with 64.9% having at least one disorder compared to 36.8% of boys; AD: 49.3% vs. 13.2%; and MD: 27.3% vs. 5.6%.

Conclusion

Adolescents living in residential group homes of the Child Welfare System in France have notably high rates of mental disorder (about three times more than those of the general population of the same age), similar to the patterns found in adolescents in North America and Europe. These data are the first of their kind in France and will guide necessary changes to the child welfare system.     

Prevalence of Adult Problem and Pathological Gambling between 2000 and 2005: An Update

Background Excessive gambling is a prominent Public Health problem with high prevalence rates in many countries. Substance abuse and other co-morbidities often constitute a major health hazard for the person which gambles with a loss of material and social resources, as well as being a major concern for his or her significant others. The present study updates and extends prevalence data to include work published between 2000 and 2005 in English and other European languages. Methods In a three-step search and exclusion process, studies with current adult prevalence rates were gathered. Results Almost all studies fulfil basic research standards. The weighted mean prevalence rates for excessive gambling (problem and pathological) are 3.0% for the South Oaks Gambling Survey (problem 1.2%; pathological 1.8%), 3.3% for the Canadian Problem Gambling Index (problem 2.4%; pathological 0.8%) and 3.1% for the DSM-IV (problem 1.9%; pathological 1.2%). Conclusion The prevalence rates are comparable and relatively stable between countries and across survey instruments, and do not differ from earlier reviews. The regular epidemiological monitoring of excessive gambling remains a major Public Health issue although the distinction between pathological and problem gambling is not appropriate for epidemiological research. Further studies are needed with respect to concomitant lifestyle characteristics.     

Statistical assessment of multivalued screening tests

When the outcome of a screening test is expressed by the probabilities of k possible outcomes among individuals with a certain physiologic condition and by the corresponding probabilities among individuals without the condition, the screening usefulness of the test depends on the relative likelihood that its result may properly alter the management of a given patient. New statistical methods are introduced to apply the screening usefulness concept to the assessment of combined or multivalued tests. The method is applied to assess the usefulness of genotypes at cytochrome P450 IAI and glutathione-S-transferase-μ as biomarkers of susceptibility to developing lung cancer. The argument and methods developed should be widely applicable to the statistical assessment of screening tests for a wide range of physiologic conditions.