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

Logarithmic 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)