Baseline characteristics of the 7185 offspring and 5307 parents are presented in Table
1. Offspring had a mean age of 30 years when they answered the RHINESSA questionnaire. The parents’ mean age was 53 years. Slightly more women than men participated, both among offspring (58%) and parents (55%). Most of the offspring had a higher education (60%), 12% were smokers, 16% had asthma and 41% had children themselves. Forty-one percent of parents smoked during the offspring’s childhood, of those 54% had on average smoked at least 10 cigarettes per day.
Table 1
Characteristics of offspring and parents
Offspring, n = 7185 |
Female, n (%) | 4147 | (57.7) |
Age, mean (SD) | 30 | (7.7) |
Smoker, n (%) | 877 | (12.2) |
Asthma, n (%) | 1157 | (16.1) |
University/College, n (%) | 4281 | (59.6) |
Secondary, n (%) | 2693 | (37.5) |
Primary, n (%) | 211 | (2.9) |
At least one child, n (%) | 2920 | (41.1) |
Parents, n = 5307 |
Female, n (%) | 2931 | (55.2) |
Age, mean (SD) | 53 | (7.2) |
Smoking during offspring’s childhood, n (%) | 2195 | (41.4) |
> 10 cig, n (%) | 1191 | (53.5) |
< 10 cig, n (%) | 1035 | (46.5) |
The sensitivity for correct offspring-reported parental smoking status during childhood (0-10years) was 0.82 (95 % CI 0.81–0.84), specificity was 0.95 (95 % CI 0.95–0.96) and a good agreement was observed κ = 0.79 (95 % CI 0.78–0.81) (Table
2). Offspring’s report of mothers’ smoking status during pregnancy showed a lower sensitivity 0.66 (95 % CI 0.60–0.71), and a slightly lower specificity 0.92 (95 % CI 0.90–0.95) compared to the analysis during childhood, and a good agreement κ = 0.61 (95 % CI 0.55–0.67) (Table
2).
Table 2
Sensitivity, specificity and Cohen’s Kappa estimate of smoking status prenatal or during offspring’s childhood
Parents’ smoking status during offspring’s childhood 0–10 years (offspring n = 7185, parents n = 5307) |
| 95% CI |
Sensitivity | 0.82 | [0.81;0.84] |
Specificity | 0.95 | [0.95;0.96] |
Cohen’s Kappa | 0.79 | [0.78;0.80] |
Mothers’ smoking status during pregnancy (offspring n = 807, mother n = 679) |
| 95% CI |
Sensitivity | 0.66 | [0.60;0.71] |
Specificity | 0.92 | [0.90;0.95] |
Cohen’s Kappa | 0.61 | [0.55;0.67] |
Multivariate logistic regression analyses (Table
3) showed that offspring’s own status as a parent was a predictor for discrepant answers, where offspring with no children had a higher disagreement (OR 2.11 [95% CI 1.21–3.69]) compared to offspring with children. Younger offspring age tended to predict discrepant answers (OR 2.03 [95% CI 0.95–4.35]) for offspring < 25 years. A lower amount of smoking was related to more discrepant answers, < 10 cigarettes per day (OR 2.72 [95% CI 1.71–4.31]) compared to 10 or more cigarettes per day. Offspring’s report of their fathers’ smoking status was also found to be a predictor for discrepant answers (OR 1.73 [95% CI 1.09–2.74]) compared to offspring’s report of their mothers’ smoking status during offspring’s childhood. Offspring’s own sex, asthma status, educational level or smoking status was not significantly related to discrepant answers.
Table 3
Predictors for discrepant answers for offspring- reported parental smoking status and parents own report of smoking
Offspring sex |
Female | 1.00 | |
Male | 1.06 | [0.66;1.70] |
Offspring asthma status |
Asthma | 1.00 | |
No asthma | 1.04 | [0.57;1.92] |
Offspring educational level |
Primary | 1.00 | |
Secondary | 4.32 | [0.64;29.20] |
University/College | 5.06 | [0.69;34.45] |
Offspring smoker status |
No | 1.00 | |
Yes | 1.42 | [0.69;2.91] |
Offspring age |
≥ 35 years | 1.00 | |
≥ 25 < 35 years | 1.30 | [0.72;2.35] |
< 25 years | 2.03 | [0.95;4.35] |
Offspring’s own parental status |
Children | 1.00 | |
No children | 2.11 | [1.21;3.67] |
Parents sex |
Mother | 1.00 | |
Father | 1.73 | [1.09;2.74] |
Parents amount of smoking |
≥ 10 cig /day | 1.00 | |
< 10 cig /day | 2.72 | [1.71;4.31] |
Sensitivity analyses
Sensitivity analyses including those who were excluded due to missing covariates produce similar results, sensitivity 0.82 (95% CI 0.81–0.84), specificity 0.95 (95% CI 0.95–0.96) and κ 0.79, (95% CI 0.77–0.80). When childhood was expanded to cover 0–18 years, similar results were also observed, sensitivity 0.82 (95% CI 0.80–0.83), specificity 0.96 (95% CI 0.95–0.96) and κ 0.79, (95% CI 0.77–0.80).
Analyses by sex showed largely similar results with a slightly lower sensitivity 0.81 (95% CI 0.79–0.83) and κ 0.78, (95% CI 0.76–0.80) and similarly specificity 0.96 (95% CI 0.95–0.97) of the fathers compared to mothers, sensitivity 0.84 (95% CI 0.82–0.86), κ 0.80, (95% CI 0.78–0.82) and specificity 0.95 (95% CI 0.94–0.96), Additional file
1: Table S1. Analyses by offspring’s own parental status showed a lower sensitivity 0.78 (95% CI 0.76–0.80), and κ 0.77, (95% CI 0.75–0.79) and similar specificity 0.96 (95% CI 0.96–0.97) of the offspring without children, compared to offspring with children, sensitivity 0.87 (95% CI 0.85–0.88), κ 0.80, (95% CI 0.77–0.82) and specificity 0.93 (95% CI 0.92–0.94).
In subgroup analyses of parents’ smoking amount, the sensitivity 0.89 (95% CI 0.88–0.91) and κ 0.85, (95% CI 0.83–0.86) were increased when the parents had smoked more than 10 cigarettes per day during their offspring’s childhood compared to the main analysis and decreased if the parents had smoked less than 10 cigarettes per day, sensitivity 0.74 (95% CI 0.72–0.76) and κ 0.72, (95% CI 0.70–0.74). The specificities remained unchanged. Separate analysis of offspring and parental predictors for disagreement produced similar results as the main analyses with offspring and parental predictors in the same model.
Further analyses of the 715 false answers in the main analysis showed a higher prevalence of false negative answers (n = 511, 71%) compared to false positive answers (n = 204, 29%), meaning that the parents had reported smoking more often than the offspring. Characteristics of offspring themselves who reported false negative answers were similar to the total study population except higher educational level (University/College 66% vs 60%), whereas offspring who reported false positive answers were slightly older and more often females (59% vs 58%), smokers (17% vs 12%), and asthmatics (18% vs 16%). Offspring who reported false negative were less likely to report regarding their mothers (49% vs 55% females) compared to the total population, whereas offspring who reported false positive answers were more likely to report regarding their mothers (60% vs 55% females). Parents’ mean age was slightly higher for offspring who reported false negative as well as false positive compared to the total population (54 and 55 vs 53 years).
Sensitivity analysis of the reversed data priority produced similar sensitivity, specificity and Cohen’s Kappa as for the main analysis.
Analyses stratified by study centre with respect to sensitivity, specificity and Cohen’s Kappa showed largely the same result as for the combined analysis; however, with wider confidence intervals with kappa ranging from 0.71 to 0.83 (Additional file
2: Table S2).