Statistics positive predictive value

Relative statistical values must govern the sequence of interpretation of a group of immunostains and should move from most to least specific or from highest to lowest positive predictive value. 

Pfizer has recently evaluated open source descriptors and model building algorithms using a training set of approximately 50 000 molecules and a test set of approximately 25 000 molecules with human liver microsomal metabolic stability data. A C5.0 decision tree model demonstrated that the Chemistry Development Kit descriptors together with a set of SMARTS keys had good statistics (Kappa = 0.43, sensitivity = 0.57, specificity 0.91, positive predicted value (PPV) = 0.64) equivalent to models built with commercial MOE2D and the same set of SMARTS keys (Kappa = 0.43, sensitivity = 0.58, specificity... 

For the entire cohort, area under the ROC curve (AUC) using the 7-point scale was 0.78 for digital and 0.74 for film. This ference was not statistically significant Sensitivity, based on the 5-point Bl-RADS scale, was 0.70 for digital mammography and 0.66 for screen-film, also not a statistically significant difference. Figure 9.2a shows the ROC curves for the entire cohort Specificity was the same for each modality at 0.92 positive predictive value for each was 0.05. 

Tables 3 and 4 are the cross-correlation matrices for the various methods and experiment, with a few positions missing because the number of molecules common to certain pairs of methods was not statistically significant. Finally, Table 5 lists the slopes and intercepts determined by linear regression of predicted values for each method against experiment for the neutral solutes. Because the experimental error is very high for the ions (at least 5 kcal/mol), the correlations in Table 4 should be analyzed with care.

In this work, all obtained models are evaluated by commonly used statistical parameters goodness-of-fit (r2) [80], root mean square error between experimental and predicted values (5) [80] by leave-one-out [81], and predictive capacity (q2) [80]. In addition, and in order to avoid chance correlations and excess of parameters, models are submitted to random tests, where the properties are randomly permuted in their positions and the entire modeling procedure is repeated a number of times, a thousand times in our case. If satisfactory correlations are found within the random test, the model obtained should not be trusted, as the methodology used may be potentially capable of correlating any kind of data. 

The percentage positive deviation statistic is the percentage of the predictions that are over predicted from perfect correlation by a technique. If a predictive technique does not have a tendency to over or under predict values, i.e. over predicts as many values as it under predicts then you would expect the percentage positive deviation to be 50%. Therefore this statistic is used as a measure of the tendency of a package to over or under estimate potency. The data reported for this statistic is the distance from 50%, i.e. if positive the technique has a tendency to over-estimate the potency, if negative the technique has a tendency to under-estimate the potency whilst the further away from zero the more exaggerated this tendency. A one sample binomial test was used to identify if the identified tendency to under or over estimate the potency was significant at the 95% confidence hmit. 

Table 1 Sensitivity and specificity of the guinea pig papillary muscle action potential assay for QT and TdP liability using APD90 or APD3o 9o as predictive biomarkers. Predictive values were calculated for three tested pacing frequencies independently from the tested concentrations for all compounds. An in vitro result is considered positive for a compound if at least one concentration showed a statistically significant and/or > 10 % increase in the selected parameter (APD90 or APD3o 9o) vs. baseline values...

In order to assess the analysis given in Figures 1 and 2 in terms of the components 1 and 2, the theoretically predicted abundances of the two components were calculated at 30 K, using the ZPVE values from Table 3. Including the statistical factors, the ratio obtained from the ZPVE s is 0.31 0.69, implying that substitution at the H2 position is slightly favoured compared to the purely statistical probability, as expected from the difference in bond strengths bewtween Cj—H and C2—H2. In a comparision with the... 

In this equation, 8 is a differential parameter developed from Sephadex and polyamide thin-layer chromatography, and ARm(3) and ARm(6) are the values for the substituents at the 3 and 6 positions, respectively. The number of compounds is sufficiently large so that the correlation could be accepted statistically. Although Equation 31 can be used to predict... 

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