R-help to Exercise 21

 

 

# The following function may be used to calculate the means, variances, coefficients of dispersion,

# Pearson X2 with corresponding P-value from the three datasets.

# Copy the commands below and paste them into R:

 

poissontab=function(counts,x=(0:(length(counts)-1)))

{

? n=sum(counts)

? meanx=sum(x*counts)/n

? varx=sum((x-meanx)^2*counts)/(n-1)

? CD=varx/meanx

? df=length(counts)-2

? px=c(dpois(0:df,meanx),1-ppois(df,meanx))

? EX=n*px

? tab=cbind(x,counts,round(EX,2),round(counts-EX,2),round((counts-EX)^2/EX,2))

? X2=sum((counts-EX)^2/EX)

? pval=1-pchisq(X2,df)

? print(paste("Mean=",round(meanx,4)))

? print(paste("Var= ",round(varx,4)))

? print(paste("CD= ",round(CD,4)))

? tab=as.data.frame(tab)

? names(tab)=c("x","Obs","Exp","O-E","(O-E)^2/E")

? print(tab)

? print(paste("Pearson X2 =",round(X2,2)))

? print(paste("p-value??? =",round(pval,4)))

}

 

 

# In order to apply the function to the first data set in the exercise, you give the commands:

yeast=c(75,103,121,54,30,13,4)

poissontab(yeast)

 

 

#Try to understand how the function produces the output given.

# Make sure you understand the output, and use the output to answer the questions in the exercise.

 

 

# Repeat the analysis for the two other data sets in the exercise.