Nov 2008 exam Act Soc India
Q. 17) As humidity influences evaporation, the solvent balance of water-reducible paints during spray-out is affected by humidity. A study is conducted to examine the relation between humidity (X) and the extent of solvent evaporation (Y). The following data summary is obtained:
n = 25, Σx = 1314.90 Σy = 235.70, Σx2 = 76,308.53, Σy2 = 2286.07 Σxy = 11,824.44
a) Find the estimated correlation coefficient between X and Y and test the
hypothesis H0 : ρ = 0, against H1 : ρ≠ 0 ; ρ being the population correlation
coefficient between X and Y.
ANSWER given at the ASI website is: r = -0.847
For testing the hypothesis H0 : ρ = 0 against H1 : ρ ≠ 0, the test statistic is
t= r (n-2)^1/2 / (1-r^2)^1/2 = -7.635
The table value of t23,0.05 is 1.714. Reject H0
MY QUESTION:
ISNT IT A 2 SIDED TEST ? IF YES, WHY t23, 0.05 is used ? IT SHOULD BE t23, 0.025 !!! assuming we are doing a 5% test.
Last edited by a moderator: May 13, 2009
