help:kruskal

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+ | [[http://www.sofastatistics.com/userguide.php | Contents]] | ||

+ | [[:help:stats_tests | Statistical Tests Available]] | ||

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+ | ====== Kruskal-Wallis H ====== | ||

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+ | [[http://en.wikipedia.org/wiki/Kruskal%E2%80%93Wallis_one-way_analysis_of_variance | Kruskal-Wallis H]] lets you decide if there is a difference in an ordinal variable e.g. user satisfaction ratings, between groups. It is the non-parametric equivalent of the [[:help:anova | ANOVA (Analysis of Variance)]] relying on value ranks rather than data values themselves. | ||

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+ | Because it is based on order rather than value, the output table displayed by SOFA shows the median instead of the mean. | ||

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+ | The p value tells you how likely the difference observed would occur if drawing from the same population (i.e. where the groups didn't really have a relationship with the value being averaged). A small p value tells you that it would be rare to observe such a difference if the group doesn't have a relationship with the value being averaged. From this we might reject the null hypothesis in favour of the alternative hypothesis - namely, that there is a difference according to the grouping variable. | ||

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+ | In the example below (based on false data for illustration only), we shouldn't be surprised the p value is very low. It is possible to see a large difference in average age and N is reasonably large for each group. In this case we could reject the hypothesis that nation has no relationship with age. | ||

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+ | {{:help:kruskal_wallis_h_example.gif|}} | ||

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+ | Be aware that there is a certain sensitivity about terminology around this area. According to a widespread convention, we shouldn't conclude that there is a relationship, only that we reject the null hypothesis (see [[http://www.stats.gla.ac.uk/steps/glossary/hypothesis_testing.html#h0 | Hypothesis testing]]). We might go so far as to reject the null hypothesis in favour of the alternative hypothesis. See [[http://en.wikipedia.org/wiki/Statistical_hypothesis_testing | Statistical hypothesis testing]]. | ||

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+ | If your data is not numeric and it is adequately normal the [[:help:anova | ANOVA (Analysis of Variance)]] is a good alternative. | ||

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+ | [[http://www.sofastatistics.com/userguide.php | Contents]] | ||

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+ | [[:help:stats_tests | Statistical Tests Available]] | ||

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+ | [[:home | Wiki]] |

help/kruskal.txt ยท Last modified: 2010/12/20 02:37 (external edit)