1 / 15

WILCOXON TEST

BIOCHEMISTRY

Download Presentation

WILCOXON TEST

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. NON- PARAMETRIC TESTS M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.

  2. Non-parametric tests • Note: When valid use parametric • Commonly used Wilcoxon Chi square etc. • Performance comparable to parametric • Useful for non-normal data • If normalization not possible • Note: CI derivation-difficult/impossible

  3. Wilcoxon signed rank test To test difference between paired data

  4. STEP 1 • Exclude any differences which are zero • Put the rest of differences in ascending order • Ignore their signs • Assign them ranks • If any differences are equal, average their ranks

  5. STEP 2 • Count up the ranks of +ives as T+ • Count up the ranks of –ives as T-

  6. STEP 3 • If there is no difference between drug (T+) and placebo (T-), then T+ & T- would be similar • If there were a difference one sum would be much smaller and the other much larger than expected • The smaller sum is denoted as T • T = smaller of T+ and T-

  7. STEP 4 • Compare the value obtained with the critical values (5%, 2% and 1% ) in table • N is the number of differences that were ranked (not the total number of differences) • So the zero differences are excluded

  8. 3rd & 4th ranks are tied hence averaged T= smaller of T+ (50.5) and T- (4.5) Here T=4.5 significant at 2% level indicating the drug (hypnotic) is more effective than placebo

  9. Wilcoxon rank sum test • To compare two groups • Consists of 3 basic steps

  10. Non-parametric equivalent of t test

  11. Step 1 • Rank the data of both the groups in ascending order • If any values are equal average their ranks

  12. Step 2 • Add up the ranks in group with smaller sample size • If the two groups are of the same size either one may be picked • T= sum of ranks in group with smaller sample size

  13. Step 3 • Compare this sum with the critical ranges given in table • Look up the rows corresponding to the sample sizes of the two groups • A range will be shown for the 5% significance level

  14. * 17, 18 & 19are tied hence the ranks are averaged

  15. THANK YOU

More Related