Bartlett' test
Silvano wrote:
Hi, I have an experiment with 5 treatments, of which 2 with 10 repetitions and 2 with 7 replications. I conducted the test of Bartlett step-by-step and compared with the value calculated directly by the R and the values are different. Anyone know tell me why?
Yes. Is mean(tapply(valor,trat,var)) the pooled variance estimate? Maybe you should look at the code of bartlett.test.default. -Peter Ehlers
#------------------- n = length(trat) I = 4 (M = 2.3026*((n-I)*log10(mean(tapply(valor,trat,var))) - (9*log10(vari[1])+9*log10(vari[2])+6*log10(vari[3])+6*log10(vari[4])))) (C = 1 + 1/(3*(4-1))*((1/9 + 1/9 + 1/6 + 1/6) - 1/(9+9+6+6))) (B = M/C)
B
1.748670
qchisq(.05, 3, lower.tail=F) # Valor tabelado
[1] 7.814728
#-----------------------------------------
# Teste de Bartlett de forma direta no R -
#-----------------------------------------
bartlett.test(valor,trat)
Bartlett test of homogeneity of variances
data: valor and trat
Bartlett's K-squared = 0.7845, df = 3, p-value =
0.8532
Thanks,
--------------------------------------
Silvano Cesar da Costa
Departamento de Estat?stica
Universidade Estadual de Londrina
Fone: 3371-4346
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