Transformation of data
Square root transformation :
Applied for data consisting of small whole numbers
Eg.: Data obtained in counting rare events such as number of infested plants in a plot, number of insects caught in traps, number of weeds /plot
It is also appropriate for percentage data where the range is 0-30% and 70-100%
Arc Sin Transformation :
Data obtained from counts and data expressed as decimal fractions or percentages .
Percentages : Range :
30-70 % : No transformation require
0-30% or 70-100% (not both): Square root transformation
Except the above rules : Arc sin transformation
Data that are whole numbers and cover wide range of values.
Eg.: Number of insects per plot / number of egg masses per plant (or per unit area)
(Source : Statistical Procedures for Agricultural Research by Kwanchai A. Gomez, Arturo A. Gomez)