Biomedical subjects

Prashni Paliwal

Publications and source records attributed to Prashni Paliwal.

7 recordsLinked to original sources

PubMed2006

Estimating measures of diagnostic accuracy when some covariate information is missing.

Many biomedical data sets are concerned with relating the result of screening procedure(s) for a clinical event to the occurrence of that event. The effect of risk factors on measures of accuracy such as positive predictive value and negative predictive value is of great interest for clinicians. In this paper we propose a generic approach to estimate these measures of accuracy in the setting where an explanatory model has been fitted to the joint screening and event outcome data but information on one or more risk factors in the model is not available. We refer to these as conditional rates, i.e. rates conditioned on only a subset of risk factors. We argue that, based upon the joint distribution of the event outcome, the screening result and the risk factor occurrence, a formal expression for such a rate can be obtained. This expression is a function of model parameters and thus can be estimated once the model has been fitted. Inference within the Bayesian framework is particularly attractive since simulation based model fitting straightforwardly yields samples from the posterior distribution of any conditional rate of interest. We perform a simulation study to compare these estimated conditional rates with frequently used ad hoc estimates. Differences can be substantial. We also illustrate the proposed methodology to compute conditional positive predictive value for a screening mammography data set. The proposed approach is also applicable when there are multiple diagnostic screening test outcomes.

Bayes Theorem↗

PubMed2006

Decreased cerebrospinal fluid allopregnanolone levels in women with posttraumatic stress disorder.

BACKGROUND: Alterations in the gamma-amino-butyric acid (GABA) neurotransmitter system have been identified in some populations with posttraumatic stress disorder (PTSD). METHODS: To further investigate factors of relevance to GABAergic neurotransmission in PTSD, we measured cerebrospinal fluid (CSF) levels of allopregnanolone and pregnanolone combined (ALLO: congeners that potently and positively modulate effects of GABA at the GABA(A) receptor), 5alpha-dihydroprogesterone (5alpha-DHP: the immediate precursor for allopregnanolone), dehydroepiandrosterone (DHEA: a negative modulator of GABA(A) receptor function), and progesterone with gas chromatography, mass spectrometry in premenopausal women with (n = 9) and without (n = 10) PTSD. Subjects were free of psychotropic medications, alcohol, and illicit drugs; all were in the follicular phase of the menstrual cycle except three healthy and four PTSD subjects receiving oral contraceptives. RESULTS: There were no group differences in progesterone, 5alpha-DHP, or DHEA levels. The PTSD group ALLO levels were < 39% of healthy group levels. The ALLO/DHEA ratio correlated negatively with PTSD re-experiencing symptoms (n = -.82, p < 008; trend) and with Profile of Mood State depression/dejection scores (n = -0.70, p < 0008). CONCLUSION: Low CSF ALLO levels in premenopausal women with PTSD might contribute to an imbalance in inhibitory versus excitatory neurotransmission, resulting in increased PTSD re-experiencing and depressive symptoms.

5-alpha-Dihydroprogesterone↗

PubMed2006

A decrease in the plasma DHEA to cortisol ratio during smoking abstinence may predict relapse: a preliminary study.

RATIONALE: Increases in depressive symptoms during smoking cessation have been associated with risk for relapse. Several studies have linked plasma levels of cortisol and dehydroepiandrosterone (DHEA) or DHEA-sulfate (DHEAS) to depressive symptoms. OBJECTIVES: To determine whether changes in plasma cortisol, DHEA, or DHEAS levels and emergence of depressive symptoms during smoking cessation are associated with smoking relapse. MATERIALS AND METHODS: Subjects were healthy non-medicated men and women, aged 39+/-12 years, who smoked, on average, 22 cigarettes per day. Depressive symptoms, smoking withdrawal symptoms, and plasma steroid levels were measured before and after 8 days of verified smoking abstinence. Relapse status at day 15 was then determined. RESULTS: In the full sample (n=63), there was a trend for changes in depressive symptoms to be associated with relapse. In the subset of 25 subjects with plasma neuroactive steroid data, there was a significant interaction between the change in the plasma DHEA/cortisol ratio from day 0 to day 8 and relapse status at day 15. This ratio was similar before abstinence, but lower at day 8 in relapsed, compared to abstinent, subjects. Changes in the DHEA/cortisol ratio tended to predict changes in depressive symptoms in the women only. CONCLUSION: A decrease in the plasma DHEA/cortisol ratio during 8 days of smoking abstinence was associated with relapse over the following week. Further research is needed to fully characterize sex-specific relationships between abstinence-induced changes in neuroactive steroid levels, depressive or withdrawal symptoms, and relapse. Such research may lead to new interventions for refractory smoking dependence.

Adult↗

PubMed2006

Examining accuracy of screening mammography using an event order model.

Screening mammography is a widely used method for breast cancer detection. For each mammogram we propose a performance model based on order of outcomes. That is, we envision an initial assessment, a follow up assessment if the initial one is positive and, eventually, a determination of whether cancer was present or not. A model can be built at each stage reflecting effects due to patient characteristics, to the facility where mammogram was performed and to the radiologist reading the mammogram. Since assessment is not perfectly associated with outcome, familiar rates of agreement and disagreement are of interest. These rates can be investigated at various levels of risk factors of interest. The approach is illustrated with screening mammography data from the Group Health Cooperative in Seattle, WA. A Bayesian framework is adopted for inference and an analysis of the data set is presented.

Adult↗

PubMed2006

Stress-induced cocaine craving and hypothalamic-pituitary-adrenal responses are predictive of cocaine relapse outcomes.

BACKGROUND: Cocaine dependence is associated with high rates of relapse. Stress and drug cue exposure are known to increase cocaine craving and stress arousal, but the association between these responses and cocaine relapse has not been previously studied. OBJECTIVE: To examine whether stress-induced and drug cue-induced cocaine craving and hypothalamic-pituitary-adrenal axis responses evoked in the laboratory are associated with subsequent cocaine relapse. DESIGN: Prospective study design assessing cocaine relapse and drug use during a 90-day follow-up period after discharge from inpatient treatment and research. Data were analyzed by Cox proportional hazards regression and multiple regression. SETTING: Inpatient treatment and research unit in a community mental health center. PATIENTS: Forty-nine treatment-seeking cocaine-dependent individuals. MAIN OUTCOME MEASURES: Time to cocaine relapse, number of days of cocaine use, and amount of cocaine used per occasion in the follow-up phase. RESULTS: Greater stress-induced, but not drug cue-induced, cocaine craving was associated with a shorter time to cocaine relapse. Stress-induced corticotropin and cortisol responses predicted higher amounts of cocaine use per occasion in the 90-day follow-up. CONCLUSIONS: These results demonstrate that stress-related increases in cocaine craving and hypothalamic-pituitary-adrenal axis responses are each associated with specific cocaine relapse outcomes. The findings support the use of stress-induced drug craving and associated hypothalamic-pituitary-adrenal axis responses to evaluate cocaine relapse propensity. Furthermore, treatments that address stress-induced cocaine craving and hypothalamic-pituitary-adrenal responses could be of benefit in improving relapse outcomes in cocaine dependence.

Adrenocorticotropic Hormone↗

PubMed2006

Meta-analysis of diagnostic and screening test accuracy evaluations: methodologic primer.

OBJECTIVE: Interest in evidence-based diagnosis is growing rapidly as diagnostic and screening techniques proliferate. In this article we provide an overview of systematic reviews of diagnostic performance and discuss in detail statistical methods for the most common variant of the problem: meta-analysis of studies in which a pair of estimates of sensitivity and specificity is reported. The need to account for possible variations in threshold for test positivity across studies led to the formulation of the Summary ROC (SROC) curve method. We discuss graphical and model-based ways to estimate, summarize, and compare SROC curves, and we present an example from a meta-analysis of data on techniques for staging cervical cancer. We also present a brief survey of the methodologic literature for addressing heterogeneity, correlated data, multiple thresholds per study, and systematic reviews of ROC studies. We conclude with a discussion of the significant methodologic challenges that continue to face investigators in this area of diagnostic medicine research. CONCLUSION: Systematic reviews of diagnostic performance are a rigorous approach to examining and synthesizing evidence in the evaluation of diagnostic and screening tests. The information from such reviews is needed by clinicians, health policy makers, researchers in diagnostic medicine, developers of diagnostic techniques, and the general public. However, despite progress in study quality and reporting and in methodologic development, major challenges confront investigators undertaking these reviews.

Diagnostic Techniques and Procedures↗

PubMed2004

The association between obesity and screening mammography accuracy.

BACKGROUND: Obesity is increasing among American women, especially as they age. The influence of obesity on the accuracy of screening mammography has not been studied extensively. METHODS: We analyzed 100 622 screening mammography examinations performed on members of a nonprofit health plan. The relationship between body mass index (weight in kilograms divided by the square of height in meters) and measures of screening accuracy was assessed. Body mass index was categorized as underweight or normal weight (<25), overweight (25-29), obesity class I (30-34), and obesity classes II to III (> or =35). RESULTS: Compared with underweight or normal weight women, overweight and obese women were more likely to be recalled for additional tests after adjusting for important covariates, including age and breast density (overweight odds ratio [OR], 1.17; 95% confidence interval [CI], 1.11-1.23); obesity class I OR, 1.27; 95% CI, 1.19-1.35; obesity classes II-III OR, 1.31; 95% CI, 1.22-1.41). As body mass index increased, women were more likely to have lower specificity (overweight OR, 0.86; 95% CI, 0.81-0.90; obesity class I OR, 0.79; 95% CI, 0.74-0.84; and obesity classes II-III OR, 0.77; 95% CI, 0.71-0.82). No statistically significant differences were noted in sensitivity. Adjusted receiver operating characteristic analysis showed statistically significant improvement in the area under the curve (AUC) for underweight or normal weight women (AUC = 0.941) vs overweight women (AUC = 0.916, P =.02) and underweight or normal weight women vs obesity classes II and III women (AUC = 0.904, P =.02). CONCLUSIONS: Obese women had more than a 20% increased risk of having false-positive mammography results compared with underweight and normal weight women, although sensitivity was unchanged. Achieving a normal weight may improve screening mammography performance.

Adult↗