Anesthetic Effectiveness

Description

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.

Usage

anesthetic

Format

This data frame contains the following columns:

move

a binary numeric vector coded for patient movement (0 = no movement, 1 = movement)

conc

anesthetic concentration

logconc

logarithm of concentration

nomove

the complement of move

Details

The interest is in estimating how the probability of jerking or twisting varies with increasing concentration of the anesthetic agent.

Source

unknown

Examples

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)