Botto-Khoury 2 × 4 table for analysis of gene × environment interactions for GSTM1 genotypes versus current ETS exposure (⩾20 cigarettes)
| Outcomes | (1) GSTM1+ and ETS− | (2) GSTM1+ and ETS+ | (3) GSTM1− and ETS− | (4) GSTM1− and ETS+ | (5) Expected OR§/departure from expected OR (†‡) |
|---|---|---|---|---|---|
| In each cell the prevalence (%) of each outcome is shown with numbers of cases and total in parentheses. Adjusted odds ratio (OR) with 95% confidence intervals, adjusted for age, sex, city, family history of asthma, hay fever, eczema and ETS exposure, are compared with the reference cell (second line of each cell). Column 1 shows the reference group without smoke exposure and without a genetic defect in the respective GST enzyme; column 2 shows the effect of GST deficiency alone; column 3 shows the isolated effect of ETS exposure in children with the intact GST gene, respectively; column 4 shows the values for the combined effect of the respective GST deficiency and concomitant ETS exposure; column 5 shows the expected OR under the assumption of a multiplicative effect, the departure from the effect, and the statistical significance of the departure from the multiplicative model. | |||||
| *p value <0.05 compared with reference group. | |||||
| †Departure from expected OR = OR in column 4 divided by the expected OR. | |||||
| ‡p value from the test for interaction from logistic regression model. | |||||
| §Expected OR is the product of the ORs in columns 2 and 3. | |||||
| Current asthma | 3.9 (29/735) | 6.1 (2/33) | 5.1 (39/758) | 8.9 (4/45) | |
| 1.0 | 2.94 (0.61 to 14.05) | 1.40 (0.85 to 2.30) | 5.48 (1.62 to 18.55)* | 4.10/1.34 (p = 0.77) | |
| Wheeze ever | 19.6 (142/725) | 24.2 (8/33) | 23.0 (172/748) | 31.1 (14/45) | |
| 1.0 | 1.81 (0.75 to 4.41) | 1.27 (0.98 to 1.64) | 2.81 (1.31 to 6.04)* | 2.30/1.22 (p = 0.71) | |
| Current wheeze | 6.5 (47/726) | 9.1 (3/33) | 8.9 (67/749) | 17.8 (8/45) | |
| 1.0 | 2.03 (0.55 to 7.54) | 1.50 (1.01 to 2.22)* | 4.74 (1.79 to 12.57)* | 3.04/1.56 (p = 0.56) | |
| Current cough without cold | 15.5 (113/727) | 12.1 (4/33) | 15.5 (117/753) | 26.1 (12/46) | |
| 1.0 | 1.04 (0.34 to 3.18) | 1.03 (0.78 to 1.37) | 2.76 (1.23 to 6.17)* | 1.07/2.58 (p = 0.15) | |