You hypothesize that physiotherapy will improve pain levels in patients with chronic back pain and undertake an evaluation of treatment outcomes. You compare pain scores measured after treatment with pain scores measured pre-treatment in a cohort of 50 patients. Assuming an alpha of 0.05, use MS Excel's =T.INV function to work out the reference critical t value. 

Report your value to one decimal place (do not enter any + or - sign in front of the number).