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Detecting Systematic Error

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An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements. The x-coordinates are calculated as follows: (7) where TN is the number of true negatives and FP is the number of false positives. doi: 10.1038/nbt0803-859. [PubMed] [Cross Ref]Kaul A. However, the values in wells, measured across all plates, can have different SDs and variances. More about the author

Centre Ville, Montreal, QC, Canada, H3C 3P8, 2McGill University and Genome Quebec Innovation Centre, 740 Dr. Many technical, procedural or environmental factors can cause systematic measurement error or inequalities in the conditions in which the measurements are taken. The exact experimental conditions of Test assay are reported in [18]. First, we generated error-free datasets consisting of random normally distributed data.

How To Reduce Random Error

After Well correction was performed, the hit selection was carried out again for the hit selection thresholds: μ-3SD and μ-2.29SD. First, three random null data sets (i.e. Statistical analysis of systematic errors in HTS. Figure 6 presents the hit distributions for the following hit selection thresholds and Figure 10S presents the hit distribution surfaces for the thresholds (, and ).

We studied the chemical structure of compounds within each well of the McMaster data set and have not found any systematic pattern in the compound distribution. This file contains Figures 1SM to 19SM presenting additional simulation results (Figures 1SM to 18SM) and an example of data distribution before and after the application of the Discrete Fourier Transform Find out more Skip Navigation Oxford Journals Contact Us My Basket My Account Bioinformatics About This Journal Contact This Journal Subscriptions View Current Issue (Volume 32 Issue 20 October 15, 2016) Random Error Calculation In Simulation 1, we carried out this test on every row and every column of each assay.

All rights reserved. Systematic Error Examples The experimental data for 164 plates were considered. Specifically, the hit detection rate as well as the false positive and the false negative rates were computed during the simulations. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3034671/ The χ2-value decreased from 2377.4 to 204.6 (with critical value equal to 111.1), i.e.

At the same time, the accuracy of the K-S test is extremely low in almost all of the considered situations. Personal Error At the same time, when the well correction was applied to the data free of noise, it did not have any negative influence to the false-positive rate (Table 1). The first step in calibrating the scale, therefore, is to adjust the scale to read zero when there is nothing on it. Navigate This Article Top Abstract 1 INTRODUCTION 2 MATERIALS AND METHODS 3 RESULTS AND DISCUSSION 4 CONCLUSION ACKNOWLEDGEMENTS Footnotes REFERENCES Search this journal: Advanced » Current Issue October 15, 2016 32

Systematic Error Examples

doi: 10.1177/001316446002000104. [Cross Ref]Fleiss JL. see here Spotting and correcting for systematic error takes a lot of care. How To Reduce Random Error Improved statistical methods for hit selection in HTS. Systematic Error Calculation Given a particular experimental procedure and setup, it doesn't matter how many times you repeat and average your measurements; the error remains unchanged.

When analyzing the obtained hits for the μ-2.29SD threshold, one can notice that 24 of the original hits were not detected and, at the same time, 30 new compounds were selected http://completeprogrammer.net/systematic-error/determinate-systematic-error.html For example, if you think of the timing of a pendulum using an accurate stopwatch several times you are given readings randomly distributed about the mean. Because the optimal parameters are sought for each well location of the assay independently, well correction has more fitting parameters than B-score and median polish. All values lower than or equal to the threshold value are considered as hits. Random Error Examples Physics

Within-plate normalization of all samples, which can be done including or excluding hits and outliers, using the Z-score transformation (i.e. Systematic error size: 10% (at most 8 columns and 8 rows affected). Accepted April 10, 2007.  Next Section Abstract Motivation: High-throughput screening (HTS) is an early-stage process in drug discovery which allows thousands of chemical compounds to be tested in a single study. http://completeprogrammer.net/systematic-error/define-systematic-error.html Compared to the four other methods, the well correction procedure was particularly accurate as to the false-negative rate (Tables 2S–4S).

We conducted a comprehensive simulation study with artificially generated HTS data, constructed to model a variety of real-life situations. Instrumental Error The B-score method improved accuracy somewhat but at the high cost of a large decrease in precision. The residual (rijp) of the measurement for row i and column j on the p-th plate is obtained by fitting a two-way median polish.

This second calibration point should be as far from the first as feasible, to establish an accurate calibration curve.

Screen 2005;10:557-567. Thus, to identify hits in the McMaster assay we applied the classical hit selection algorithm based on the assay mean and SD (Method 2) and the well correction procedure (Method 5). There are many advantages to this approach, including that thresholds do not need to be determined in advance. Zero Error Definition View larger version: In this window In a new window Download as PowerPoint Slide Fig. 3.

The basic data format adopted here was that of the McMaster dataset - 1250 plates, each containing 96 wells arranged in 8 rows and 12 columns. The curves were obtained for the standard normal data with 1% of added hits without (a) and with (b) systematic error. Survey of applications of combinatorial technologies. navigate to this website Each value on the graphic depicts the number of hits found at the associated well.

HTS identifies novel inhibitors of Escherichia coli dihydrofolate reductase that are competitive with dihydrofolate. The detailed analysis of the McMaster hit distributions obtained for different thresholds is presented in the section 3.2. 2.5 Compared methods The five following methods were compared in this study. IFCS 2006, Studies in Classification, Data Analysis, and Knowledge Organization, Springer Verlag; 2006b. Visual and computational analysis of structure-activity relationships in high-throughput screening data.

J. A systematic error (an estimate of which is known as a measurement bias) is associated with the fact that a measured value contains an offset.