Use of ROC curve analysis for prediction gives fallacious results: Use predictivity-based indices.

ABSTRACT: The area under the ROC curve is frequently used for assessing the predictive efficacy of a model, and the Youden index is commonly used to provide the optimal cut-off. Both are misleading tools for predictions. A ROC curve is drawn for the sensitivity of a quantitative test against its (1 - specificity) at different values of the test. Both sensitivity and specificity are retrospective in nature as these are indicators of correct classification of already known conditions. They are not indicators of future events and are not valid for predictions. Predictivity intimately depends on the prevalence which may be ignored by sensitivity and specificity. We explain this fallacy in detail and illustrate with several examples that the actual predictivity could differ greatly from the ROC curve-based predictivity reported by many authors. The predictive efficacy of a test or a model is best assessed by the percentage correctly predicted in a prospective framework. We propose predictivity-based ROC curves as tools for providing predictivities at varying prevalence in different populations. For optimal cut-off for prediction, in place of the Youden index, we propose a P-index where the sum of positive and negative predictivities is maximum after subtracting 1. To conclude, for correctly assessing adequacy of a prediction models, predictivity-based ROC curves should be used instead of the usual sensitivity-specificity-based ROC curves and the P-index should replace the Youden index.

Optimising plasma clozapine levels to improve treatment response: an individual patient data meta-analysis and receiver operating characteristic curve analysis.

BACKGROUND: Although clozapine is the most efficacious medication for treatment-refractory schizophrenia, not all patients will have an adequate response. Optimising clozapine dose using therapeutic drug monitoring could therefore maximise response. AIMS: Using individual patient data, we undertook a receiver operating characteristic (ROC) curve analysis to determine an optimal therapeutic range for clozapine levels to guide clinical practice. METHOD: We conducted a systematic review of PubMed, PsycINFO and Embase for studies that provided individual participant level data on clozapine levels and response. These data were analysed using ROC curves to determine the prediction performance of plasma clozapine levels for treatment response. RESULTS: We included data on 294 individual participants from nine studies. ROC analysis yielded an area under the curve of 0.612. The clozapine level at the point of optimal diagnostic benefit was 372 ng/mL; at this level, the response sensitivity was 57.3%, and specificity 65.7%. The interquartile range for treatment response was 223-558 ng/mL. There was no improvement in ROC performance with mixed models including patient gender, age or length of trial. Clozapine dose and clozapine concentration to dose ratio did not provide significantly meaningful prediction of response to clozapine. CONCLUSIONS: Clozapine dose should be optimised based on clozapine therapeutic levels. We found that a range between 250 and 550 ng/mL could be recommended, while noting that a level of >350 ng/mL is the most optimal for response. Although some patients may not respond without clozapine levels >550 ng/mL, the benefits should be weighed against the increased risk of adverse drug reactions.

Lepra tuberculoide borderline en paciente con reacción lepromatosa tipo eritema nudoso simulando un síndrome de Sweet / Borderline Tuberculoid Leprosy in Erythema Nodosum Leprosum Reaction Mimicking Sweet's Syndrome

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Pápulas y placas pruriginosas persistentes y eritema flagelado como manifestaciones de una enfermedad de Still del adulto / Persistent Pruritic Papules AND Plaques and Flagellate Erythema as Presenting Manifestations of an Adult onset Still's Disease

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Lupus miliar diseminado de la cara / Lupus Miliaris Disseminatus Faciei

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Ausencia congénita de uñas y pulgar digitalizado debida a la exposición prenatal a fenitoína / Congenital Absence of Nails and Digital-Type Thumb due to Prenatal Phenytoin Exposure

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Vesículas perimenstruales recurrentes en el interior de la oreja. Una presentación inusual / Recurrent Perimenstrual Vesicles Inside the Ear: A Rare Presentation

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Nail changes due to chemotherapy: a prospective observational study of 129 patients.

BACKGROUND: Nail changes due to systemic drugs are common, especially with anticancer treatments due to involvement of nail plate, nail bed and periungual area. OBJECTIVE: To study the pattern of nail changes occurring due to chemotherapy in patients suffering from various malignancies. MATERIALS AND METHODS: A prospective, observational study was conducted at various health care centres, Nashik, India, for 15 months. The timing of administration of chemotherapy and onset of nail changes were recorded and evaluated by a dermatologist at regular interval. RESULTS: A total of 129 diagnosed cases of various malignancies who received chemotherapy were included. The most common malignancy noted was breast cancer, that is n = 42 (32.5%) followed by oral cancer, that is n = 24 (18.6%). Chemotherapy agents included taxanes (n = 54), cyclophosphamide (n = 42) and prednisolone (n = 28). Nail changes were noted in 92 patients (71.3%). The most common nail changes observed were chromonychia (n = 70, 54.26%), followed by nail dystrophy (n = 38, 29.45%). CONCLUSION: Nail toxicity is quite common side effect of anticancer agents. Nail changes due to chemotherapy depend on the nail structure involved and the severity of insult. Awareness among dermatologists and oncologists of these nail changes and their culprit agent can promote early diagnosis and may avoid inadvertent measures.

Evaluation of Emblica officinalis fruit powder as a growth promoter in commercial broiler chickens.

AIM: The present study was conducted to evaluate the dietary addition of Emblica officinalis (Amla) fruit powder as a growth promoter in commercial broiler chickens. MATERIALS AND METHODS: An experiment was conducted on 135 commercial broiler chicks (Ven-Cobb 400 strain) divided into three groups with three replicates of 15 chicks each. Three treatment groups were as follows - T1: Basal diet as per BIS standards; T2: Basal diet supplemented with 0.4% of E. officinalis fruit powder; and T3: Basal diet supplemented with 0.8% of E. officinalis fruit powder. RESULTS: The average body weights at the end of the 6(th) week were significantly higher (p<0.05) in groups T2 and T3 compared to group T1. Feed intake, feed conversion ratio and feed cost per kg live weight production were similar among the treatment groups. The net profit per bird was the highest in group T2 (Rs. 19.22/bird) followed by group T3 (Rs. 17.86/bird) and the lowest in group T1 (Rs. 14.61/bird). CONCLUSION: Based on the results of the present study, it was concluded that dietary addition of E. officinalis (Amla) fruit powder had a positive effect on growth performance and net profit per bird in commercial broiler chickens.