Matched set (or pair)
Disease (1, case; 2, control)
Some chracteristics of the child: sex (1, male; 2, female), Down’s
syndrome (a known risk factor for leukemia; 1, no; 2, yes), age
Risk factors related to the use of x-ray: MXray (mother ever had
x-ray during pregnancy; 1, no; 2, yes), UMXray (mother ever had
upper-body x-ray during pregnancy; 0, no; 1, yes), LMXray (mother
ever had lower-body x-ray during pregnancy; 0, no; 1, yes), FXray
(father ever had x-ray; 1, no; 2, yes), CXray (child ever had x-ray; 1,
no; 2, yes), CNXray (child’s total number of x-rays; 1, none; 2, 1–2;
3, 3–4; 4, 5 or more)
(a)Taken collectively, do the covariates contribute significantly to the
separation of cases and controls?
(b)Fit the multiple regression model to obtain estimates of individual
regression coe‰cients and their standard errors. Draw conclusions
concerning the conditional contribution of each factor.
(c)Within the context of the multiple regression model in part (b),
does gender alter the e¤ect of Down’s syndrome?
(d)Within the context of the multiple regression model in part (b),
taken collectively, does the exposure to x-ray (by the father, or
mother, or child) relate significanty to the disease of the child?
(e)Within the context of the multiple regression model in part (b), is
the e¤ect of age linear?
(f)Focus on Down’s syndrome as the primary factor, taken collec-
tively; was this main e¤ect altered by any other covariates?444 ANALYSIS OF SURVIVAL DATA