Botto-Khoury 2 × 4 table for analysis of gene × environment interactions for GSTT1 genotypes versus current ETS exposure (⩾20 cigarettes)
| Outcomes | (1) GSTT1+ and ETS− | (2) GSTT1+ and ETS+ | (3) GSTT1− and ETS− | (4) GSTT1− 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 the 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 | 4.8 (59/1238) | 7.5 (5/67) | 3.5 (9/255) | 9.1 (1/11) | |
| 1.0 | 3.25 (1.14 to 9.27)* | 0.73 (0.35 to 1.50) | 4.10 (0.43 to 39.04) | 2.37/1.73 (p = 0.67) | |
| Wheeze ever | 21.8 (266/1222) | 25.4 (17/67) | 19.1 (48/251) | 45.5 (5/11) | |
| 1.0 | 1.77 (0.92 to 3.42) | 0.84 (0.60 to 1.19) | 4.37 (1.17 to 16.39)* | 1.49/2.93 (p = 0.13) | |
| Current wheeze | 7.9 (96/1222) | 13.4 (9/67) | 7.1 (18/253) | 18.2 (2/11) | |
| 1.0 | 2.61 (1.09 to 6.21)* | 0.90 (0.53 to 1.52) | 3.30 (0.61 to 17.91) | 2.34/1.41 (p = 0.71) | |
| Current cough without cold | 15.4 (189/1228) | 16.2 (11/68) | 16.3 (41/252) | 45.5 (5/11) | |
| 1.0 | 1.50 (0.71 to 3.20) | 1.08 (0.74 to 1.56) | 6.72 (1.77 to 25.52)* | 1.62/4.15 (p = 0.05) | |