" Exercise 5.4
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 J. Baverstock, Rothamsted Research
Version 1, 20/08/2014 "
" Set working directory - change to location of your data file "
\set [workingdirectory='d:/stats4biol/data/']
" Read data from working directory "
FILEREAD [NAME='FUNGUS.DAT'; IMETHOD=read] FGROUPS=no,yes,no
" Reorder levels of factor Treatment so that Control is the 3rd level "
FACAMEND FACTOR=Fungus; NEWLEVELS=!(1,3,2)
" Bartlett's test "
VHOMOGENEITY [PRINT=test,variance; GROUPS=Fungus] DATA=Nymphs
" Verify calculation "
SCALAR N; VALUE=NVAL(Nymphs)
SCALAR t; VALUE=NLEVELS(Fungus)
" Get sample variances and replication "
TABULATE [CLASSIFICATION=Fungus; COUNT=Tc] Nymphs; VARIANCE=Tvar
PRINT Tc,Tvar; DECIMALS=0,2
VTABLE Tvar,Tc; VARIATE=Vvar,Vc
" Get pooled estimate of variance "
CALCULATE Pooled = SUM((Vc-1)*Vvar)/SUM(Vc-1)
PRINT Pooled; DECIMALS=2
" Calculate scalar for Bartlett statistic "
CALCULATE c = (SUM(1/(Vc-1))-1/(N-t))/(3*(t-1))
PRINT c; DECIMALS=3
" Calculate test statistic "
CALCULATE X2 = ((N-t)*log(Pooled)-SUM((Vc-1)*log(Vvar)))/(1+c)
PRINT X2; DECIMALS=3
" Get 95th percentile of Chisquared distribution on 2 df "
PRINT EDCHI(0.95;2); DECIMALS=3
" Get observed significance level "
PRINT CUCHI(X2;2); DECIMALS=3
" End of File "