The correction for bias in prevalence estimation with screening tests

Estimation of the dispersal distances of an aphid-borne virus in a patchy landscape

Characterising the spatio-temporal dynamics of pathogens in natura is key to ensuring their efficient prevention and control. However, it is notoriously difficult to estimate dispersal parameters at scales that are relevant to real epidemics. Epidemiological surveys can provide informative data, but parameter estimation can be hampered when the timing of the epidemiological events is uncertain, and in the presence of interactions between disease spread, surveillance, and control. Further complications arise from imperfect detection of disease and from the huge number of data on individual hosts arising from landscape-level surveys. Here, we present a Bayesian framework that overcomes these barriers by integrating over associated uncertainties in a model explicitly combining the processes of disease dispersal, surveillance and control. Using a novel computationally efficient approach to account for patch geometry, we demonstrate that disease dispersal distances can be estimated accurately in a patchy (i.e. fragmented) landscape when disease control is ongoing. Applying this model to data for an aphid-borne virus (Plum pox virus) surveyed for 15 years in 605 orchards, we obtain the first estimate of the distribution of flight distances of infectious aphids at the landscape scale. About 50% of aphid flights terminate beyond 90 m, which implies that most infectious aphids leaving a tree land outside the bounds of a 1-ha orchard. Moreover, long-distance flights are not rare-10% of flights exceed 1 km. By their impact on our quantitative understanding of winged aphid dispersal, these results can inform the design of management strategies for plant viruses, which are mainly aphid-borne.

Comparative Test Evaluation: Methods and Challenges

The present paper has three objectives. First, methods for comparing alternative tests for the purpose of replacement of one test with a second presumably superior test are described. Second, problems in the interpretation of the relevance of different diagnostic thresholds (thresholds of positivity) that define who is and who is not a disordered gambler are examined and a potential solution offered in the form of a common quantitative measure of the risk of being a disordered gambler. Third, alternative methodologies are described as potential solutions to the lack of a gold or reference standard in the evaluation of new tests.

Test Performance Variation Between Settings and Populations

The present paper is the third in a series on the evaluation of new tests designed to detect the disordered gambler. The present paper has two objectives. First, the observed variation in test performance between settings and populations is described in general terms and an explanation of the observed variation is presented in terms of what is referred to as spectrum effects. Second the expected variation in test performance between settings and populations is illustrated with several examples and the implications emphasized for the purpose of test evaluation.

Diagnostic utility of brain activity flow patterns analysis in attention deficit hyperactivity disorder

BACKGROUND

A previous small study suggested that Brain Network Activation (BNA), a novel ERP-based brain network analysis, may have diagnostic utility in attention deficit hyperactivity disorder (ADHD). In this study we examined the diagnostic capability of a new advanced version of the BNA methodology on a larger population of adults with and without ADHD.

METHOD

Subjects were unmedicated right-handed 18- to 55-year-old adults of both sexes with and without a DSM-IV diagnosis of ADHD. We collected EEG while the subjects were performing a response inhibition task (Go/NoGo) and then applied a spatio-temporal Brain Network Activation (BNA) analysis of the EEG data. This analysis produced a display of qualitative measures of brain states (BNA scores) providing information on cortical connectivity. This complex set of scores was then fed into a machine learning algorithm.

RESULTS

The BNA analysis of the EEG data recorded during the Go/NoGo task demonstrated a high discriminative capacity between ADHD patients and controls (AUC = 0.92, specificity = 0.95, sensitivity = 0.86 for the Go condition; AUC = 0.84, specificity = 0.91, sensitivity = 0.76 for the NoGo condition).

CONCLUSIONS

BNA methodology can help differentiate between ADHD and healthy controls based on functional brain connectivity. The data support the utility of the tool to augment clinical examinations by objective evaluation of electrophysiological changes associated with ADHD. Results also support a network-based approach to the study of ADHD.

Impaired Decision-Making, Higher Impulsivity, and Drug Severity in Substance Dependence and Pathological Gambling

OBJECTIVES

Substance use disorder is characterized by impaired decision making, impulsivity, and risk taking. Pathological gambling shares many of these characteristics, and having both diagnoses may be associated with greater problems than either diagnosis alone. We investigated whether among substance-dependent individuals, comorbid pathological gambling would be associated with worse decision making, greater impulsivity, risk taking, and drug severity.

METHODS

Ninety-six substance-dependent individuals were recruited from a residential treatment program and divided into 1 of the 2 groups depending on whether they met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, criteria for pathological gambling (SDPG, n = 26) or not (SD, n = 70). Ninety-two controls were recruited from the community. Participants completed a decision-making task (modified Iowa Gambling Task), measures of impulsivity (Barratt Impulsivity Scale and Delay Discounting), and risk taking (Balloon Analog Risk Task). Decision making was analyzed using a computational model. We tested for group differences using analysis of covariance or Kruskal-Wallis and appropriate post-hoc tests.

RESULTS

The groups differed in decision-making parameters (P < 0.001) and self-reported impulsivity (P < 0.001). All post-hoc comparisons were significant on these measures, and indicated stepwise changes in controls, followed by SD, followed by SDPG, with SDPG performing worse on decision making and being more impulsive. Compared with SD, SDPG had greater drug severity (P < 0.001). No group differences were observed in delay discounting or risk taking.

CONCLUSIONS

Compared with individuals with substance dependence without pathological gambling, those with both disorders demonstrated worse decision making and significantly more drug-related symptoms. When evaluating patients with substance dependence, clinicians should consider diagnostic assessments for gambling, as the co-occurrence of both disorders may impact clinical characteristics.

Attention Deficit Hyperactivity Disorder Symptoms, Comorbidities, Substance Use, and Social Outcomes among Men and Women in a Canadian Sample

Background. Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that can persist in adolescence and adulthood. Aim. To examine prevalence of ADHD symptoms and correlates in a representative sample of adults 18 years and older living in Ontario, Canada. Method. We used the Centre for Addiction and Mental Health Monitor, an ongoing cross-sectional telephone survey, to examine the relationships between ADHD positive symptoms and comorbidities, substance use, medication use, social outcomes, and sociodemographics. Results. Of 4014 residents sampled in 2011-2012, 3.30% (2.75%–3.85%) screened positively for ADHD symptoms (women = 3.6%; men = 3.0%). For men, distress, antisocial symptoms, cocaine use, antianxiety medication use, antidepressant medication use, and criminal offence arrest were associated with positive ADHD screen. For women, distress, cocaine use, antianxiety medication use, antidepressant medication use, pain medication use, and motor vehicle collision in the past year were associated with positive ADHD screen. Conclusions. ADHD symptoms are associated with adverse medical and social outcomes that are in some cases gender specific.

The validation of screening tests: meet the new screen same as the old screen?

The focus of this report is to examine the process of validation of new screening tests designed to detect the problem gambler in research and practice settings. A hierarchical or phases of evaluation model is presented as a conceptual framework to describe the basic features of the validation process and its implications for application and interpretation of test results. The report describes a number of threats to validity in the form of sources of unintended bias that when unrecognized may lead to incorrect interpretations of study results and the drawing of incorrect conclusions about the usefulness of the new screening tests. Examples drawn from the gambling literature on problem gambling are used to illustrate some of the more important concepts including spectrum bias and clinical variation in test accuracy. The concept of zones of severity and the bias inherent in selecting criterion thresholds are reviewed. A definition of reference or study gold standard is provided. The use of 2-stage designs to establish validity by efficiently using reference standards to determine indices of accuracy and prevalence is recommended.

Estimating the prevalence of drinking problems among physicians

OBJECTIVE

Surveys assessing alcohol use among physicians have most commonly employed the Alcohol Use Disorders Identification Test (AUDIT) or the AUDIT-C, the most common short version of the AUDIT. As with other screeners, prevalence estimation is dependent on the accuracy of the test as well as choice of the cutoff value. The aim of the current study is to derive more precise prevalence estimates of alcohol problems in physicians by correcting for false-positive and false-negative results.

METHOD

In the context of a survey, the AUDIT was sent out via email or standard postal service to all 2484 physicians in Salzburg, Austria. A total of 456 physicians participated. A published correction formula was used to estimate the real prevalence of alcohol use problems.

RESULTS

Applying a cutoff of 5 points for the AUDIT-C, 15.7% of female and 37.7% of male physicians screened positive. Use of a correction based on general population data and the sensitivity and specificity of the AUDIT-C resulted in much lower prevalence rates: 4.0% for female and 9.5% for male physicians. Using the full AUDIT, 19.6% of the female physicians and 48% of the male physicians were screened positive. Using the correction, the estimated prevalence rates for females and males were 6.3% and 15.5%, respectively.

CONCLUSIONS

Our findings demonstrate that uncorrected screening results may markedly overestimate the prevalence of physicians drinking problems.

Validating the gambling functional assessment--revised in a United kingdom sample

The gambling functional assessment-revised (GFA-R) was designed to assess whether the respondent's gambling was maintained by positive reinforcement or escape. The present study attempted to validate the GFA-R's psychometric properties using United Kingdom (UK) university students and to compare the results to those from a sample of American university students. Two hundred seventy four UK students completed the GFA-R, and 153 also completed the South Oaks gambling screen (SOGS). Two hundred one United States (US) university students completed both measures. A confirmatory factor analysis indicated that the original model of the GFA-R provided an excellent fit for the UK data and internal consistency was high. These outcomes were similar, if not superior, to those from the US sample. SOGS scores strongly correlated with GFA-R escape subscale scores in both samples, replicating previous results. These findings indicate that the GFA-R is a valid measure for use in the UK, which is potentially useful to both practitioners and researchers. They also suggest that the strong relationship between endorsing gambling as an escape and measures of disordered gambling may be ubiquitous.

The Relationship between Endorsing Gambling as an Escape and the Display of Gambling Problems

Previous research has reported a strong relationship between endorsing gambling as an escape and problem/pathological gambling as measured by the South Oaks Gambling Screen (SOGS). The present study recruited 249 university students to complete the Gambling Functional Assessment-Revised (GFA-R), which measures the function of the respondent's gambling, as well as the SOGS and the Problem Gambling Severity Index (PGSI), which was designed to identify gambling problems in the general population. Endorsing gambling as an escape on the GFA-R was again predictive of SOGS scores. The function of one's gambling was also predictive of the respondents' PGSI scores, but whether gambling for positive reinforcement or as an escape was the significant predictor differed between male and female respondents. Scores on the GFA-R subscales also accounted for a significant amount of variance in PGSI scores above and beyond that accounted for by SOGS scores. The present results support the idea that both practitioners and researchers should be interested in the function of an individual's gambling as well as the presence or the absence of pathology. They also suggest that differences in the function of gambling might also exist between the sexes.

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.

A test of the false positive bias hypothesis

An evaluation of the hypothesis that adolescent gamblers are biased toward the production of false positive responses proposed by Derevensky et al. was tested. The results of secondary analysis of available data supported the hypothesis for items on the South Oaks Gambling Screen and items from the DSM-IV screening instrument. The conclusions were presented as tentative in view of the modest sizes of the observed effects. A number of limitations to the analysis are also described.

The South Oaks Gambling Screen (SOGS): A rebuttal to critics

A review of the literature reveals strong support for the construct validity of interpretations based on scores obtained with the original and more recent versions and/or variants of the South Oaks Gambling Screen (SOGS). Criticisms of the SOGS are shown to lack merit, to be offset by more important criteria, or to be no longer relevant. The evidence reviewed indicates that the construct of pathological gambling as represented by the SOGS and its variants provides a robust definition and implies that the SOGS meets the important criterion of validity generalization. The construct of chasing and behaviors related to chasing is shown to provide powerful measures by which to discriminate between the presence and absence of pathological gambling. The viability of the SOGS to continue to make important contributions to the understanding of pathological gambling is discussed in terms of the criteria for selecting a research instrument.

Interpreting prevalence estimates of pathological gambling: Implications for policy

Some guidelines for interpreting prevalence estimates for the purpose of establishing the number of pathological gamblers in the community are presented. The analysis is based on the concept of the likelihood ratio, a recommended procedure for validating criteria for defining cases based on test scores. It is shown that the likelihood ratio can be employed with available estimates of prevalence to translate cut-off scores into positive predictive value. Those cut-off scores associated with high positive predictive values provide an empirical measure of confidence that those gamblers who meet or exceed the cut-off criterion are pathological gamblers. A potential limitation of the analysis is the possible specificity of results to the validation studies employed to compute likelihood ratios and to the specific estimates of prevalence used to determine positive predictive value. A recommendation is presented for obtaining study- or community-specific validation evidence.

Using the Rasch model to develop a revised Gambling Attitudes and Beliefs Scale (GABS) for use with male college student gamblers

Research suggests that an overwhelming majority of college students gamble, with between 2-9% of U.S. students meeting DSM-IV criteria for pathological gambling. Despite the prevalence of gambling among college students, accurate and easily implemented methods for the assessment of gambling involvement among college students are lacking. Thus, the purpose of the current study was to establish the psychometric properties of a measure of gambling attitudes and beliefs (GABS) and demonstrate this measure's association with gambling frequency and an established gambling screen among 374 U.S. male college students during 1995-1997. Using techniques based in modern test theory (e.g., Rasch model), we identified a set of 10 items that reliably rank-ordered students in relation to their positive attitudes and beliefs about gambling. Further, the resulting 10 items accounted for variance in gambling behavior beyond that provided by a more standard consequences-based assessment measure. Use of this measure for the improvement of gambling assessment in college students is recommended.

Is the SOGS an accurate measure of pathological gambling among children, adolescents and adults?

The South Oaks Gambling Screen (SOGS) is widely used to assess the prevalence of pathological gambling. For a variety of reasons, this instrument may not provide an accurate rate of the prevalence of pathological gambling. In this paper, one source of error in data provided by the SOGS is investigated. It is argued that individuals may not fully understand the meaning of some items, and that clarification of the meaning of misunderstood items may in some cases lead to a changed score on the scale. The present study evaluates respondents' understanding of the SOGS items. The results from three studies are reported, each using a different sample: grade school children, adolescents and adults. It was hypothesised that (1) participants would not understand some items of the SOGS, (2) problem gamblers and probable pathological gamblers would be more inclined to interpret items incorrectly than would non-problem gamblers and, (3) consistent with the first two hypotheses, clarification of items would decrease the number of participants identified as problem gamblers or probable pathological gamblers. The data obtained supported hypotheses 1 and 3. Furthermore, hypothesis 2 was supported for grade school children, but not for adolescents or adults. These results are consistent with recent literature on endorsement and acquiescence phenomena, and have implications for prevalence studies of probable pathological gambling.

Using the Rasch model to evaluate the South Oaks Gambling Screen for use with nonpathological gamblers

Despite its utility for the dichotomous differentiation of pathological and nonpathological gamblers, some have questioned the use of the South Oaks Gambling Screen (SOGS) for discriminating individuals across the entire range of gambling problems. Using methods from item response theory, we derived a six-item version of the SOGS. This shortened version of the SOGS performed uniformly across a sample of pathological gamblers and a sample of students and resulted in five levels of discrimination and the following interpretation: a score of 1 reveals potential for problems; 2 reveals likely problem gambling; 3 or 4 items endorsed represent significant levels of problems noticeable by others; while 5 or 6 represents severe problems with significant financial involvement. We discuss the implications and remaining limitations of using this shortened measure for the continuum-based assessment of gambling problems.

A Reply to Gambino's "An Epidemiologic Note on Verification Bias: Implications for Estimation of Rates"

While two-stage designs in problem gambling research are expensive and relatively difficult to execute, they have the potential to yield more accurate prevalence estimates as well as valuable additional information about gambling and problem gambling in the community. However, gains in precision are heavily dependent on the accuracy of the screening methods used and the sample sizes involved. Sound practice requires reliable information about the variances and confidence levels associated with different screens. In the spirit of contributing to the ongoing dialog about ways to improve the measurement of problem gambling, we examine several reasons to question whether the revised estimates offered by Gambino are in fact an improvement.

Interference with PDK1-Akt survival signaling pathway by UCN-01 (7-hydroxystaurosporine)

3-Phosphoinositide-dependent protein kinase-1 (PDK1) plays a central role in activating the AGC subfamily of protein kinases. In particular, PDK1 plays an important role in the regulation of Akt/PKB survival pathway by phosphorylating Akt on Thr308. Here we show that UCN-01 (7-hydroxystaurosporine), a drug now in clinical trials and with a unique fingerprint pattern, induced dephosphorylation and inactivation of Akt, resulting in the turn-off of the survival signals and the induction of apoptosis. Further analysis revealed that UCN-01-mediated Akt inactivation was caused by inhibiting upstream Akt kinase PDK1 (IC50=33 nM) both in vitro and from cells, but not by suppressing Akt itself or phosphatidylinositide-3-OH kinase. UCN-01-induced PDK1 inhibition was also observed in in vivo murine and human tumor xenografts. Overexpression of active form of Akt diminished the cytotoxic effects of UCN-01, suggesting that UCN-01 may in part exert its cytotoxicity by inhibiting PDK1-Akt survival pathway. Because UCN-01 has already proved to have potent anti-tumor activity in vivo, PDK1-Akt survival pathway is a new, attractive target for cancer chemotherapy.

Role of cAMP, PKA and Rap1A in thyroid follicular cell survival

Cyclic AMP (cAMP) rescues cells from apoptosis stimulated by diverse insults. We examined the role of cAMP as a survival factor, and the signaling pathways through which cAMP affords protection. Rat thyroid cells were selected for these studies given the predominant role of cAMP in thyrotropin (TSH)-stimulated proliferation and as an oncogene in thyroid cells. Wistar rat thyroid (WRT) cells perished via apoptosis following sodium nitroprusside (SNP) treatment. Elevations in cAMP following treatment with forskolin, 8BrcAMP or IBMX rescued cells from SNP-induced cell death. Notably, TSH prevented apoptosis, implicating an important role for this hormone as a survival factor. Cyclic AMP activates multiple signaling pathways including those mediated through PKA, PI3K, p70S6k and the Ras-related small G protein, Rap1. Intriguingly, multiple pathways modulate thyroid cell survival. Interference with cAMP-stimulated p70S6k, but not PI3K, activity abrogated cell survival. Treatment with PKA inhibitors was sufficient to stimulate apoptosis in hormone-deprived cells and markedly enhanced cell death in response to SNP. Cells expressing an activated Rap1A mutant exhibited an enhanced sensitivity to SNP-induced apoptosis, while those expressing dominant negative Rap1A were resistant to SNP-initiated cell death. Together, these findings establish an important role for PKA and Rap1 in the control of thyroid cell survival.

Expression of the oncogenic NPM-ALK chimeric protein in human lymphoid T-cells inhibits drug-induced, but not Fas-induced apoptosis

Anaplastic large cell lymphomas (ALCLs) are frequently associated with the t(2;5)(p23;q35) translocation, leading to the expression of NPM-ALK, a fusion protein linking nucleophosmin and anaplastic lymphoma kinase, a receptor tyrosine kinase. In ALCLs, dimerization of NPM-ALK leads to constitutive autophosphorylation and activation of the kinase, necessary for NPM-ALK oncogenicity. To investigate whether NPM-ALK, like other oncogenic tyrosine kinases, can inhibit drug-induced apoptosis, we permanently transfected NPM-ALK into Jurkat T-cells. As in ALCLs, NPM-ALK was expressed as a constitutively kinase-active 80 kDa protein, and could be detected by immunocytochemistry in nucleoli, nuclei and cytoplasm. Doxorubicin-induced apoptosis (assessed by cell morphology and annexin V-FITC binding) was significantly inhibited in two independent NPM-ALK-expressing clones (5.2+/-1.8 and 7.5+/-0.8% apoptosis), compared to control vector-transduced cells (36+/-6.7%). Similar results were observed with etoposide. In contrast, Fas-induced apoptosis was not inhibited. Cytochrome c release into the cytosol was delayed in doxorubicin-, but not anti-Fas-treated transfectant cells, indicating that apoptosis inhibition occurred upstream of mitochondrial events. Using NPM-ALK mutants, we demonstrated that inhibition of drug-induced apoptosis: (1) requires functional kinase activity, (2) does not involve phospholipase C-gamma, essential for NPM-ALK-mediated mitogenicity and (3) appears to be phosphoinositide 3-kinase independent, despite a strong Akt/PKB activation observed in wild type NPM-ALK-expressing cells. These results suggest that the NPM-ALK antiapoptotic and mitogenic pathways are distinct.

Modulation of cellular apoptotic potential: contributions to oncogenesis

The importance of apoptosis as a natural means to eliminate unwanted or damaged cells has been realized over the past decade. Many components required to exercise programmed cell death have been identified and shown to pre-exist in most, if not all, cells. Such ubiquity requires that apoptosis be tightly controlled and suggests the propensity of cells to trigger the cellular death machinery can be regulated. Recently, several signaling pathways have been demonstrated to impact the apoptotic potential of cells, most notably the phosphatidylinositol 3' kinase (PI3'K) pathway. The 3' phosphorylated lipid products generated by this enzyme promote activation of a protein-serine kinase, PKB/AKT, which is necessary and sufficient to confer cell PI3'K-dependent survival signals. The relevance of this pathway to human cancer was revealed by the recent finding that the product of the PTEN tumor suppressor gene acts to antagonize PI3'K. This review focuses on the regulation and mechanisms by which PKB activation protects cells and the oncologic consequences of dysregulation of the pathway.