Aberrant Crypt Foci in Rat Colons

Description

Numbers of aberrant crypt foci (ACF) in the section 1 of the colons of 22 rats subjected to a single dose of the carcinogen azoxymethane (AOM), sacrificed at 3 different times.

Usage

ACF1

Format

This data frame contains the following columns:

count

Observed number of ACF in section 1 of each rat colon

endtime

Time of sacrifice, in weeks following injection of AOM

Source

Ranjana P. Bird, Faculty of Human Ecology, University of Manitoba, Winnipeg, Canada.

References

E.A. McLellan, A. Medline and R.P. Bird. Dose response and proliferative characteristics of aberrant crypt foci: putative preneoplastic lesions in rat colon. Carcinogenesis, 12(11): 2093-2098, 1991.

Examples

sapply(split(ACF1$count,ACF1$endtime),var)
plot(count ~ endtime, data=ACF1, pch=16)
pause()
print("Poisson Regression - Example 8.3")
ACF.glm0 <- glm(formula = count ~ endtime, family = poisson, data = ACF1)
summary(ACF.glm0)

# Is there a quadratic effect?
pause()

ACF.glm <- glm(formula = count ~ endtime + I(endtime^2),
  family = poisson, data = ACF1)
summary(ACF.glm)

# But is the data really Poisson?  If not, try quasipoisson:
pause()

ACF.glm <- glm(formula = count ~ endtime + I(endtime^2),
  family = quasipoisson, data = ACF1)
summary(ACF.glm)