> fT <- function(r, n) { + r * sqrt((n - 2)/(1 - (r^2))) + } > r1 <- 0.78 > n1 <- 80 > fT(r1, n1)
[1] 11.00831
> qt(0.975, 78)
[1] 1.990847Outro exemplo (não está nas notas de aula) Suponha as seguintes variáveis A e B
> set.seed(123) > a<-rnorm(10) > b<-1:10 > cor.test(a,b)
Pearson's product-moment correlation data: a and b t = -0.7622, df = 8, p-value = 0.4678 alternative hypothesis: true correlation is not equal to 0 95 percent confidence interval: -0.7645707 0.4418019 sample estimates: cor -0.2602059
> fT(cor(a,b),10)
[1] -0.7622297
> qt(0.975,8) # t tabelado
[1] 2.306004
> pt(-.7622,8)*2 # p-valor
[1] 0.467815
> psico <- read.table("psico.txt", h = T) > attach(psico) > plot(x, y, pch = 16, xlab = "idade", ylab = "tempo de reação")
> modelo <- lm(y ~ x, data = psico) > summary(modelo)
Call: lm(formula = y ~ x, data = psico) Residuals: Min 1Q Median 3Q Max -7.500 -4.125 -0.750 2.625 10.500 Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 80.5000 5.4510 14.768 1.67e-11 *** x 0.9000 0.1769 5.089 7.66e-05 *** --- Signif. codes: 0 `***´ 0.001 `**´ 0.01 `*´ 0.05 `.´ 0.1 ` ´ 1 Residual standard error: 5.593 on 18 degrees of freedom Multiple R-squared: 0.5899, Adjusted R-squared: 0.5672 F-statistic: 25.9 on 1 and 18 DF, p-value: 7.662e-05
> anova(modelo)
Analysis of Variance Table Response: y Df Sum Sq Mean Sq F value Pr(>F) x 1 810.00 810.00 25.897 7.662e-05 *** Residuals 18 563.00 31.28 --- Signif. codes: 0 `***´ 0.001 `**´ 0.01 `*´ 0.05 `.´ 0.1 ` ´ 1
> par(mfrow = c(1, 2)) > plot(modelo$fitted.values, modelo$resid, pch = 16, xlab = "preditos", + ylab = "resíduos") > plot(x, modelo$resid, pch = 16, xlab = "xi", ylab = "resíduos")
> par(mfrow = c(1, 1)) > qqnorm(modelo$res) > qqline(modelo$res)
> plot(psico$x, psico$y, xlab = "idade", ylab = "tempo de reação") > medias <- c(mean(y[x == 20]), mean(y[x == 25]), mean(y[x == 30]), + mean(y[x == 35]), mean(y[x == 40])) > points(unique(x), medias, pch = 16) > xe <- 20:40 > ye <- 80.5 + 0.9 * xe > lines(xe, ye)ou
> plot(psico$x, psico$y, xlab = "idade", ylab = "tempo de reação") > abline(modelo)ou
> plot(psico$x, psico$y, xlab = "idade", ylab = "tempo de reação") > lines(x, modelo$fit, col = 2)
> new <- data.frame(x = seq(28, 28, 1)) > predict(lm(y ~ x, data = psico), new, interval = "confidence", + level = 0.95)
fit lwr upr 1 105.7 102.9696 108.4304