A quick intro to finding percentiles and areas for the t distribution using R (a free statistical software package), using the commands qt and pt.

A quick intro to finding percentiles and areas for the t distribution using R (a free statistical software package), using the commands qt and pt.

Hi,

while calculating 5’th percentile in a t distribution , we are using .05 in qt .

My query is – since qt refers to the area to the left , so should we not be using 5/2’th percentile , i.e .025 in qt function to calculate 5’th percentile. So each tail has 2.5th percentile

The 5th percentile is, by the definition of a percentile, the value of the variable that has an area to the left of 0.05. So here, where I want to find the 5th percentile, I use the qt(.05,df) command. It is true that in some other scenarios we want to find the t values that give us a combined area in the two tails of 0.05, but then we would be looking for the 2.5th percentile and the 97.5th percentile.