Anesthetic Effectiveness
Thirty patients were given an anesthetic agent maintained at a predetermined level (conc) for 15 minutes before making an incision. It was then noted whether the patient moved, i.e. jerked or twisted.
anesthetic
This data frame contains the following columns:
a binary numeric vector coded for patient movement (0 = no movement, 1 = movement)
anesthetic concentration
logarithm of concentration
the complement of move
The interest is in estimating how the probability of jerking or twisting varies with increasing concentration of the anesthetic agent.
unknown
print("Logistic Regression - Example 8.1.4")
z <- table(anesthetic$nomove, anesthetic$conc)
tot <- apply(z, 2, sum) # totals at each concentration
prop <- z[2, ]/(tot) # proportions at each concentration
oprop <- sum(z[2, ])/sum(tot) # expected proportion moving if concentration had no effect
conc <- as.numeric(dimnames(z)[[2]])
plot(conc, prop, xlab = "Concentration", ylab = "Proportion", xlim = c(.5,2.5),
ylim = c(0, 1), pch = 16)
chw <- par()$cxy[1]
text(conc - 0.75 * chw, prop, paste(tot), adj = 1)
abline(h = oprop, lty = 2)
pause()
anes.logit <- glm(nomove ~ conc, family = binomial(link = logit),
data = anesthetic)
anova(anes.logit)
summary(anes.logit)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.