29 Aug 2011

Comparing Two Distributions

Here I compare two distributions, flowering duration of indigenous and allochtonous plant species. The hypothesis is that alien compared to indigenous plant species exhibit longer flowering periods.

11 Aug 2011

Test Difference between Two Proportions & Plot Confidence Intervals

..an illustrative example for testing proportions and presenting the results.

the data: number of indigenous and alien plant species with and without vegetative reproduction (N = 3399, mid-european species, data-courtesy: BiolFlor) . Hypothesis: The proportion of species with vegetative reproduction is different between alien and indigenuos plant species.

result:  the prop. of plants with veg. reproduction is sign. lower for alien compared to indigenous plant species. this is simply due to the large number of agricultural weeds and contaminants within alien species - these species almost always reproduce by seeds.

8 Aug 2011

Two-Way PERMANOVA (adonis, vegan-Package) with Customized Contrasts

...say you have a multivariate dataset and a two-way factorial design - you do a PERMANOVA and the aov-table (adonis is using ANOVA or "sum"-contrasts) tells you there is an interaction - how to proceed when you want to go deeper into the analysis?
You could, however somewhat tedious, customize contrasts for the PERMANOVA and check for differences between certain level combinations.