" Exercise 2.5 Statistical Methods in Biology: Design and Analysis of Experiments and Regression by S.J. Welham, S.A. Gezan, S.J. Clark & A. Mead (2014) Chapman & Hall/CRC Press, Boca Raton, Florida. ISBN: 978-1-4398-0878-8 Data from H.-C. Jing & K. Hammond-Kosack, Rothamsted Research Version 1, 16/09/2014 " " Set working directory - change to location of your data file " \SET [WORKINGDIRECTORY='d:/stats4biol/data/'] " Read data from working directory " FILEREAD [NAME='TRITICUM.DAT'; IMETHOD=read] FGROUPS=no " Plot data " DGRAPH Y=Weight; X=Length " Sample statistics " DESCRIBE [SELECTION=mean,var] DATA=Weight,Length PRINT STRUCTURE=COV(Weight;Length) " Correlation coefficient & test " FCORRELATION [PRINT=correlation,test] DATA=Weight,Length " Rest of file verifies calculations " " Verify calculation of sample variances and covariance " CALCULATE N = NVAL(Weight) CALCULATE DevWt = Weight-MEAN(Weight) CALCULATE DevLn = Length-MEAN(Length) CALCULATE VarWt = SUM(DevWt*DevWt)/(N-1) CALCULATE VarLn = SUM(DevLn*DevLn)/(N-1) CALCULATE Cov = SUM(DevWt*DevLn)/(N-1) PRINT VarWt, VarLn, Cov; DEC=4 " Calculation of correlation coefficient " CALCULATE Corr = Cov/sqrt(VarWt*VarLn) PRINT Corr; DEC=3 " Calculate t statistic " CALCULATE t = Corr*sqrt((N-2)/(1-Corr**2)) PRINT t; DEC=3 " Get 5% critical value for two-sided test = 97.5th quantile of t distribution with 10 df " CALCULATE critical = EDT(0.975;N-2) PRINT critical; DEC=3 " Get observed significance level for test = proportion of t distribution with 10 df > abs(t) or < -abs(t) " CALCULATE P = 2*CUT(ABS(t);n[1]+n[2]-2) PRINT P; DEC=4 " End of File "