Logistic Regression: A Self-learning Text, Third Edition (Statistics in the Health Sciences)

Variable Abbreviation Coding

Smoking status SMK 1 ¼ever, 0¼never

Number of sexual

partners

NS 1 ¼ 4 þ,0¼0–3

Age at first intercourse AS 1 ¼ 20 þ,0¼ 19

PRINTOUT:

Model I

2lnL^¼174.97

Variable b S.E. Chi sq P

SMK 1.4361 0.3167 20.56 0.0000

NS 0.9598 0.3057 9.86 0.0017

AS 0.6064 0.3341 3.29 0.0695

Model II

2lnL^¼171.46

Variable b S.E. Chi sq P

SMK 1.9381 0.4312 20.20 0.0000

NS 1.4963 0.4372 11.71 0.0006

AS 0.6811 0.3473 3.85 0.0499

SMKNS 1.1128 0.5997 3.44 0.0635

Variance–Covariance Matrix(Model II)

SMK NS AS SMKNS

SMK 0.1859

NS 0.1008 0.1911

AS 0.0026 0.0069 0.1206

SMKNS 0.1746 0.1857 0.0287 0.3596

1. What method of estimation was used to obtain esti-
   mates of parameters for both models, conditional or
   unconditional ML estimation? Explain.


2. Why are the variables, age and socioeconomic status,
   missing from the printout, even though these were
   variables matched on in the study design?


3. For Model I, test the hypothesis for the effect of SMK
   on cervical cancer status. State the null hypothesis in

160 5. Statistical Inferences Using Maximum Likelihood Techniques