## 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
The number of ACF observed 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)