Hello everyone! welcome to my tutorial page hosted on GitHub. Here, I have complied some basic tutorial of statistical and phylogenetic analysis. Statistical analysis can be execute in R statistical programming. Different free softwares can be used for phylogenetic analysis.
Two-way ANOVA test is used to evaluate simultaneously the effect of two grouping variables (A and B) on a response variable. Assumption of Two-way ANOVA: response variables are normally distributed and have equal variance across groups
You can use the ToothGrowth data available in R. The ToothGrowth data consists of tooth growth values when Guinea pigs are treated with two types of delivery methods of vitamin C and at three different dose level of vitamin C. Here, grouping variables: (i) delivary method of vitamin C and (ii) different dose level.
Now before checking homogeneity of variace across group change the dose to categorical variable in ToothGrowth data fix(ToothGrowth). Click dose header and select type as character. Check whether variance is same across group or not?
p-value is greater than 0.05. It means data has homogeneity of variace across groups.
The p-value of supp is 0.000231 (significant), which indicates that the levels of supp are associated with significant different tooth length. The p-value of dose is < 2e-16 (significant), which indicates that the levels of dose are associated with significant different tooth length. The p-value for the interaction between supp*dose is 0.02 (significant), which indicates that the relationships between dose and tooth length depends on the supp method.