1 / 14

Lecture 14 Non-parametric hypothesis testing

Lecture 14 Non-parametric hypothesis testing. Spiders on Mazurian lake islands. The ranking of data. Disturbance. The ranking of data eliminates outliers and non-linearities . In most cases it reduces within group variances . All parametric tests can be applied to ranked data!.

rufin
Télécharger la présentation

Lecture 14 Non-parametric hypothesis testing

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. Lecture14 Non-parametrichypothesistesting Spiders on Mazurianlakeislands The ranking of data Disturbance The ranking of data eliminatesoutliers and non-linearities. In most casesitreduceswithin group variances. All parametrictestscan be applied to ranked data!

  2. Effects of ranking Ranking oftenreducesthewithin group variances.

  3. Pairedcomparisons of themean; Wilcoxon’smatchedpairsrank test TheWicoson test isthenon-parametricalternative to theone-wayrepeatedmeasures ANOVA W z isapproximatelynormallydistributed. Past uses a differentalgorithm for the same test.

  4. Sign test

  5. Therank test of Withney and Mann – U-test Spiderabundances Expectedmeanif no difference Expected SE if no difference The U-test isthenonparametricalternative to thet-test.

  6. Ranked data Raw data As in the case of the t-test does the ranked ANOVA result in lower significance levels. Ranking levels off the within group heterogeneity (lower within group variance). The test is less conservative.

  7. Kruskal-Wallis test or Kruskal-Wallis one wayANOVA by ranks Raw data ANOVA KW is approximately χ2 distributed. Values can be taken from a c2 table with r-1 degrees of freedom

  8. The ANOVA gavethemoreconservativeresult

  9. Random skewers Diversity of groundbeetlesalong an elevational gradient We take 1000 random samples and calculateeach time Spearman’srank order correlation.

  10. Ifthereis no trend inspeciesrichness we expect a Bernoulli distribution of positive and negativecorrelations. Of 1000 rankcorrelations 623 werepositive. The associated probabilityis It’shighlyprobablethatthereis a altitudinal trend inspeciesrichness.

  11. Home work and literature • Refresh: • U-test • Wilcoxonmatchedpairs test • Sign test • Kruskal Wallis test • Raw and ranked data • Tiedranks Literature: Łomnicki: Statystyka dla biologów http://statsoft.com/textbook/

More Related