Table 3

Logistic Regression Results, odds ratios comparing likelihood of response.

Variable

OR

95% CI

P-value


Main effects only


Notify: Postcard vs. Letter

1.04

0.77

1.39

0.80


Pages: 2 vs 4

0.81

0.60

1.09

0.16


Age: 1 year increase

1.03

1.01

1.04

0.0001


Sex: Female vs Male

1.86

1.38

2.50

<.0001


Race: White vs non-white*

3.35

1.77

6.35

0.0002


Race: White vs other/unknown

2.23

1.49

3.35

0.0001



Including interaction between survey length and age


Notify: Postcard vs. Letter

1.05

0.78

1.42

0.73


Pages: 2 vs 4 (for 25-year-olds)

0.34

0.19

0.62

0.0004


Pages: 2 vs 4 (for 35-year-olds)

0.53

0.36

0.79

0.0015


Pages: 2 vs 4 (for 45-year-olds)

0.84

0.62

1.13

0.25


Pages: 2 vs 4 (for 55-year-olds)

1.32

0.87

2.00

0.19


Sex: Female vs Male

1.86

1.38

2.50

<.0001


Race: White vs non-white*

3.40

1.79

6.47

0.0002


Race: White vs other/unknown

2.33

1.55

3.50

<.0001


Notes: Age was modeled continuously, therefore, the significant interaction in the second model was summarized by calculating the odds ratios at select points across the age range. P-value for survey length-by-age interaction = 0.001. There was no significant interaction found between notification method and survey length (p = 0.25).

* "Non-white" includes: American Indian/Alaskan Native, Black or African American, Native Hawaiian/Pacific Islander, and Asian.

Beebe et al. BMC Medical Research Methodology 2010 10:50   doi:10.1186/1471-2288-10-50

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