Sample-size dependence of validation parameters in linear regression models and in QSAR.

The dependence of statistical validation parameters was investigated on the size of the sample taken in fit of multivariate linear curves. We observed that R2 and related internal parameters were misleading as they overestimated the goodness-of-fit of models at small sample size. Cross-validation metrics showed correct trends. It was possible to scale the leave-one-out and the leave-many-out results close to identical by correcting the degrees of freedom of the models. y and x-randomized validation parameters were calculated and the methods provided close to identical results. We suggest to use the simplest methods in both cases. The external parameters followed correct trends with respect to the sample size, but their sensitivity differed. We plotted the Roy-Ojha metrics in 2D and we coloured them with respect to other external parameters to provide an easy classification of models. The rank correlations were calculated between the performance parameters. Up to a sample size, goodness-of-fit and robustness were distinguishable, but above a certain sample size, the parameters were redundant. The external-internal pairs were weakly correlated. Our data show that all the three aspects of validation are necessary at small sample sizes, but the internal check of robustness is not informative above a given sample size.

Increased Lipocalin 2 level may have important role in thrombotic events in patients with polycythemia vera and essential thrombocythemia.

The aim of our study was to evaluate the possible effect of lipocalin 2 on thrombotic events in polycythemia vera and essential thrombocythemia patients. The samples of 89 patients were collected and RNA based method was used to evaluate the relative gene expression level of lipocalin 2. 74 samples were available for evaluation. Drawing a cut off point at level 30 relative expression rate, 13 patients with elevated lipocalin 2 expression had thrombotic events during the course of their disease. Based on these data high lipocalin 2 expression level seems to have strong positive predictive value on thrombotic events in patients with polycythemia vera and essential thrombocythemia. Lipocalin 2 may be useful in thrombotic risk stratification in these patients.

Measuring couplings in crowded NMR spectra: pure shift NMR with multiplet analysis.

The PSYCHE method for pure shift NMR is exploited to generate 2D J spectra with full decoupling in one dimension and multiplet structure in the other, allowing spin-spin coupling constants to be measured even in very crowded spectra. Significant improvements over existing techniques are demonstrated for the hormones estradiol and androstenedione.