Biostatistics

564 CHAPTER 11 REGRESSION ANALYSIS: SOME ADDITIONAL TECHNIQUES
been considered. The final model contains all of the independent variables that meet the
inclusion criteria.
Backward Elimination This model-building procedure begins with all of the
variables in the model. This strategy also builds a model using correlations and a
predetermined inclusion criterion based on the F statistic. The first variable considered
for removal from the model is the one with the smallest partial correlation coefficient. If
this variable does not meet the criterion for inclusion, it is eliminated from the model. The
next variable to be considered for elimination is the one with the next lowest partial
correlation. It will be eliminated if it fails to meet the criterion for inclusion. This procedure
continues until all variables have been considered for elimination. The final model contains
all of the independent variables that meet the inclusion criteria.
EXERCISES
11.3.1 Refer to the data of Exercise 10.3.2 reported by Son et al. (A-6), who studied family caregiving in
Korea of older adults with dementia. The outcome variable, caregiver burden (BURDEN), was
measured by the Korean Burden Inventory (KBI) where scores ranged from 28 to 140 with higher
scores indicating higher burden. Perform a stepwise regression analysis on the following independent
variables reported by the researchers:
CGAGE: caregiver age (years)
CGINCOME: caregiver income (Won-Korean currency)
CGDUR: caregiver-duration of caregiving (month)
ADL: total activities of daily living where low scores indicate the elderly perform activities
independently.
MEM: memory and behavioral problems with higher scores indicating more problems.
COG: cognitive impairment with lower scores indicating a greater degree of cognitive impairment.
SOCIALSU: total score of perceived social support (25–175, higher values indicating more
support). The reported data are as follows.
CGAGE CGINCOME CGDUR ADL MEM COG SOCIALSU BURDEN
41 200 12 39 4 18 119 28
30 120 36 52 33 9 131 68
41 300 60 89 17 3 141 59
35 350 2 57 31 7 150 91
37 600 48 28 35 19 142 70
42 90 4 34 3 25 148 38
49 300 26 42 16 17 172 46
39 500 16 52 6 26 147 57
49 309 30 88 41 13 98 89
40 250 60 90 24 3 147 48
(Continued )