lecture-22-handouts - 11/3/2011 Practical Bioinformatics...

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11/3/2011 1 Practical Bioinformatics for Life Scientists Week 11, Lecture 22 István Albert Bioinformatics Consulting Center Penn State p-values defined When are two values different in a in a reliable (statistically significant) way? p-value the probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true. test statistic numerical summary of the data null hypothesis no change/no relationship p-values - common pitfalls 1. it is not a measure of magnitude or quality 2. it is very sensitive to the number of measurements 3. it is very sensitive to systematic errors 4. does not account for the upper bounds 5. cannot properly account for (latent) multiple testing 6. cannot point to biologically relevant effects 7. my personal observation everything can be made statistically significant if you try hard enough On p-values and statistical significance It’s not just you very few people understand p-values, even fewer can apply them correctly
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lecture-22-handouts - 11/3/2011 Practical Bioinformatics...

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