Description Usage Format Details Source Examples
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.
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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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | 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)
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