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ST5213

Appendix: R output

Chi-square statistics

> round(qchisq(0.05,  df=1:130,  lower.tail  =  FALSE),  3)

[1]

3.841

5.991

7.815

9.488

11.070

12.592

14.067

15.507

16.919

18.307

[11]

19.675

21.026

22.362

23.685

24.996

26.296

27.587

28.869

30.144

31.410

[21]

32.671

33.924

35.172

36.415

37.652

38.885

40.113

41.337

42.557

43.773

[31]

44.985

46.194

47.400

48.602

49.802

50.998

52.192

53.384

54.572

55.758

[41]

56.942

58.124

59.304

60.481

61.656

62.830

64.001

65.171

66.339

67.505

[51]

68.669

69.832

70.993

72.153

73.311

74.468

75.624

76.778

77.931

79.082

[61]

80.232

81.381

82.529

83.675

84.821

85.965

87.108

88.250

89.391

90.531

[71]

91.670

92.808

93.945

95.081

96.217

97.351

98.484

99.617

100.749

101.879

[81]

103.010

104.139

105.267

106.395

107.522

108.648

109.773

110.898

112.022

113.145

[91]

114.268

115.390

116.511

117.632

118.752

119.871

120.990

122.108

123.225

124.342

[101]

125.458

126.574

127.689

128.804

129.918

131.031

132.144

133.257

134.369

135.480

[111]

136.591

137.701

138.811

139.921

141.030

142.138

143.246

144.354

145.461

146.567

[121]

147.674

148.779

149.885

150.989

152.094

153.198

154.302

155.405

156.508

157.610

Question 1

> library(Sleuth3)

> dat <- ex2012

> str(dat)

’data.frame’: 120 obs. of 3 variables:

$ Group: Factor w/ 2 levels "Case","Control": 2 2 2 2 2 2 2 2 2 2 ...

$ CK : int 52 20 28 30 40 24 15 22 42 130 ...

$ H : num 83.5 77 86.5 104 83 78.8 87 91 65.5 80.3 ...

> levels(dat$Group)

[1] "Case" "Control"

> dat$Group <- relevel(dat$Group, ref="Control")

> str(dat)

’data.frame’: 120 obs. of 3 variables:

$ Group: Factor w/ 2 levels "Control","Case": 1 1 1 1 1 1 1 1 1 1 ...

$ CK : int 52 20 28 30 40 24 15 22 42 130 ...

$ H : num 83.5 77 86.5 104 83 78.8 87 91 65.5 80.3 ...

> range(dat$CK) [1] 15 925

> range(dat$H) [1] 34 118

> plot(CK ~ H, dat, pch=as.character(as.numeric(Group)))

40 60 80 100 120

H

> plot(log(CK) ~ H, dat, pch=as.character(as.numeric(Group)))

40 60 80 100 120

H

> (fm <- glm(Group ~ CK + H, family = binomial, data=dat))

Call: glm(formula = Group ~ CK + H, family = binomial, data = dat)

Coefficients:

(Intercept)

CK

H

-16.16695

0.06838

0.12732

Degrees of Freedom: 119 Total (i.e. Null); 117 Residual Null Deviance: 149.8

Residual Deviance: 62.22 AIC: 68.22

> (fm1  <- update(fm, .~. + I(H^2)))

Call: glm(formula = Group ~ CK + H + I(H^2), family = binomial, data = dat) Coefficients:

(Intercept) CK H I(H^2)

-32.806114 0.069289 0.494264 -0.002002

Degrees of Freedom: 119 Total (i.e. Null); 116 Residual Null Deviance: 149.8

Residual Deviance: 61.68 AIC: 69.68

> anova(fm, fm1, test = "Chisq") Analysis of Deviance Table

Model 1: Group ~ CK + H

Model 2: Group ~ CK + H + I(H^2)

Resid. Df Resid. Dev Df Deviance Pr(>Chi)

1

117

62.224

2

116

61.675 1

0.54905 0.4587

> (fm1  <- update(fm, .~. + I(CK^2)))

Call: glm(formula = Group ~ CK + H + I(CK^2), family = binomial, data = dat) Coefficients:

(Intercept) CK H I(CK^2)

-1.664e+01 7.859e-02 1.292e-01 -7.130e-05

Degrees of Freedom: 119 Total (i.e. Null); 116 Residual Null Deviance: 149.8

Residual Deviance: 61.79 AIC: 69.79

> anova(fm, fm1, test = "Chisq") Analysis of Deviance Table

Model 1: Group ~ CK + H

Model 2: Group ~ CK + H + I(CK^2)

Resid. Df Resid. Dev Df Deviance Pr(>Chi)

1

117

62.224

2

116

61.789 1

0.43496 0.5096

> (fm1  <- update(fm, .~. + I(H*CK)))

Call: glm(formula = Group ~ CK + H + I(H * CK), family = binomial, data = dat)

Coefficients:

(Intercept)

CK

H

I(H * CK)

-10.05172

-0.05812

0.05818

0.00147

Degrees of Freedom: 119 Total (i.e. Null); 116 Residual Null Deviance: 149.8

Residual Deviance: 61.13 AIC: 69.13

> anova(fm, fm1, test = "Chisq")

Analysis of Deviance Table

Model 1: Group ~ CK + H

Model 2: Group ~ CK + H + I(H * CK)

Resid. Df Resid. Dev Df Deviance Pr(>Chi)

1

117

62.224

2

116

61.128 1

1.0961

0.2951

> drop1(fm, test = "Chisq")

Single term deletions Model:

Group ~ CK + H

Df  Deviance AIC LRT Pr(>Chi)

62.224 68.224

CK 1 128.168   132.168   65.944  4.64e-16

H 1 85.647 89.647   23.423  1.30e-06

> (fm <- glm(Group ~ log(CK) + H, family = binomial, data=dat))

Call: glm(formula = Group ~ log(CK) + H, family = binomial, data = dat)

Coefficients:

(Intercept)

log(CK)

H

-28.9134

4.0204

0.1365

Degrees of Freedom: 119 Total (i.e. Null); 117 Residual Null Deviance: 149.8

Residual Deviance: 61.99 AIC: 67.99

> (fm1  <- update(fm, .~. + I(H^2)))

Call: glm(formula = Group ~ log(CK) + H + I(H^2), family = binomial,  data = dat)

Coefficients:

(Intercept)

log(CK)

H

I(H^2)

-39.511498

3.987467

0.376885

-0.001328

Degrees of Freedom: 119 Total (i.e. Null); 116 Residual Null Deviance: 149.8

Residual Deviance: 61.75 AIC: 69.75

> anova(fm, fm1, test = "Chisq") Analysis of Deviance Table

Model 1: Group ~ log(CK) + H

Model 2: Group ~ log(CK) +  H  +  I(H^2) Resid. Df Resid. Dev