s08_2 - Statistics 224/324 - lecture 1 (Bates) Midterm 2...

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Unformatted text preview: Statistics 224/324 - lecture 1 (Bates) Midterm 2 2008-04-10 (p. 1) The kfm data set from the text gives the milk intake (dl/day) of 50 infants approximately 2 months old; 25 girls and 25 boys. boy girl 5 6 7 8 9 10 Milk intake (dl/day) Density 0.0 0.1 0.2 0.3 4 6 8 10 12 boy girl Standard normal quantiles Milk intake (dl/day) 5 6 7 8 9 10-2-1 1 2 > with(kfm, summary(dl.milk)) Min. 1st Qu. Median Mean 3rd Qu. Max. 4.440 6.555 7.660 7.504 8.428 10.430 > with(kfm, c(variance = var(dl.milk), std.dev. = sd(dl.milk))) variance std.dev. 2.284666 1.511511 > t.test(dl.milk ~ sex, kfm, conf.level = 0.99) Welch Two Sample t-test data: dl.milk by sex t = 2.174, df = 47.89, p-value = 0.03468 alternative hypothesis: true difference in means is not equal to 0 99 percent confidence interval:-0.2095362 2.0015362 sample estimates: mean in group boy mean in group girl 7.9524 7.0564 The article Pavement thickness designs for no-fines concrete parking lots ( J. of Transportation Engr. , 1995: 476-484) provided data from an experiment measuring y = porosity (%) as it relates to x = unit weight (pcf) in concrete specimens. Unit weight (pcf) Porosity (%) 10 15 20 25 100 105 110 115 120 Fitted values Residuals-1 1 10 15 20 25 30 Standard normal quantiles Residuals-1 1-2-1 1 2 Statistics 224/324 - lecture 1 (Bates) Midterm 2 2008-04-10 (p. 2) > summary(fm1 <- lm(porosity ~ weight, concrete)) Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 118.90992 4.49912 26.43 1.10e-12 weight-0.90473 0.04109-22.02 1.12e-11 Residual standard error: 0.938 on 13 degrees of freedom Multiple R-squared: 0.9739, Adjusted R-squared: 0.9719 F-statistic: 484.8 on 1 and 13 DF, p-value: 1.125e-11 > confint(fm1) 2.5 % 97.5 % (Intercept) 109.1901530 128.6296806 weight-0.9934966-0.8159647 > anova(fm1) Df Sum Sq Mean Sq F value Pr(>F) weight 1 426.62 426.62 484.84 1.125e-11 Residuals 13 11.44 0.88 > unlist(predict(fm1, list(weight = 115), se = TRUE)) fit.1 se.fit df residual.scale 14.8658911 0.3357749 13.0000000 0.9380352 > qt(c(0.05, 0.025, 0.01, 0.005), df = 13, lower = FALSE) [1] 1.770933 2.160369 2.650309 3.012276 A consumer product-testing organization wishes to compare the annual power consumption for different brands of dehumidifier. Because power consumption depends on the prevailing humidity level, it was decided to monitor each brand at four different levels of humidity ranging from mod- erate to very high humidity. Each brand was tested at each humidity level and the annual power consumption (kWh) recorded....
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s08_2 - Statistics 224/324 - lecture 1 (Bates) Midterm 2...

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