Table 1.
Descriptive statistics of the study sample from the ALSPAC by sex
| Characteristics, median (P25–P75), mean (SD) or na (%) | Boys (n = 1030) | Girls (n = 1236) | P |
|---|---|---|---|
| Potential confounders | |||
| Maternal educational achievement (n = 2124) | |||
| Low level (none, CSE and vocational) | 155 (16.0) | 191 (16.5) | |
| Intermediate level (O-level) | 330 (34.0) | 410 (35.5) | 0.659 |
| High level (A-level, university degree) | 484 (50.0) | 554 (48.0) | |
| Parental social classb (n = 2059) | |||
| Professional and intermediate (class I and class II) | 636 (68.0) | 722 (64.3) | |
| Skilled non-manual (class III non-manual) | 197 (21.0) | 264 (23.5) | 0.219 |
| Skilled manual, partly and unskilled (class III manual, class IV and class V) | 103 (11.0) | 137 (12.2) | |
| Maternal age (years) (n = 2095) | 29.5 (4.4) | 29.2 (4.4) | 0.225 |
| Maternal anxiety during pregnancy (n = 2064) | 164 (17.4) | 193 (17.4) | 0.949 |
| Maternal smoking during pregnancy (n = 1976) | 148 (16.5) | 186 (17.3) | 0.633 |
| Parity (n = 2117) | 459 (47.4) | 571 (49.7) | 0.277 |
| Pre-term delivery (<37 weeks of gestation) (n = 2168) | 52 (5.3) | 40 (3.4) | 0.031 |
| Birthweight (grams) (n = 2138) | 3500 (3140–3860) | 3400 (3100–3680) | <0.001 |
| Breastfeeding for 3 months or more (n = 2064) | 582 (61.0) | 700 (63.1) | 0.337 |
| Family furry pets (cat/dog) during first year (n = 2040) | 385 (41.4) | 484 (43.6) | 0.334 |
| Dietary energy intake at 10 years (kcal/day) (n = 2175) | 1927 (1701–2178) | 1770 (1561–2000) | <0.001 |
| Body mass index at 11 years (kg/m2) (n = 2226) | 18.0 (16.5–20.2) | 18.5 (16.8–21.0) | <0.001 |
| Weight statusc (n = 2226) | |||
| Healthy weight (Z-score <1.04) | 729 (71.9) | 890 (73.4) | |
| Overweight (Z-score ≥1.04–1.63) | 139 (13.7) | 155 (12.8) | 0.710 |
| Obese (Z-score ≥1.64) | 146 (14.4) | 167 (13.8) | |
| Lean body mass index at 11 years (kg/m2) (n = 2210) | 13.2 (12.6–13.9) | 12.6 (11.9–13.5) | <0.001 |
| Fat mass index at 11 years (kg/m2) (n = 2210) | 3.7 (2.6–5.8) | 5.0 (3.5–7.0) | <0.001 |
| Smoking status at 14 years (n = 1916) | 8 (1.0) | 18 (1.7) | 0.173 |
| Pubertal status | |||
| Age of menarche (in years) (n = 1195) | – | 12.4 (1.1) | |
| Early age (<11.3 years) | 238 (19.9) | ||
| Average age (≥11.3–13.5 years) | 774 (64.8) | ||
| Late age (>13.5 years) | 183 (15.3) | ||
| Voice-breaking status (n = 1013) | |||
| Completely broken | 577 (57.0) | – | |
| Starting to break | 329 (32.5) | ||
| Not yet started | 107 (10.5) | ||
| Height at 15 years (cm) (n = 2246) | 174.3 (169.0–179.0) | 164.6 (160.6–168.9) | <0.001 |
| Lifetime doctor-diagnosed asthma (n = 2265) | 259 (25.2) | 267 (21.6) | 0.045 |
| Spirometry measures | |||
| 8 years | |||
| FVC (L) (n = 1995) | 2.0 (0.3) | 1.8 (0.3) | <0.001 |
| FEV1 (L) (n = 1972) | 1.7 (0.3) | 1.6 (0.3) | <0.001 |
| FEF25–75 (L/s) (n = 1995) | 2.0 (0.5) | 2.1 (0.5) | 0.032 |
| FEV1/FVC (%) (n = 1972) | 87.2 (6.7) | 89.4 (6.0) | <0.001 |
| Z-score of FVC (n = 1831) | –0.05 (1.00) | –0.06 (0.99) | 0.943 |
| Z-score of FEV1 (n = 1809) | –0.05 (1.02) | –0.01 (0.98) | 0.299 |
| Z-score of FEF25–75 (n = 1831) | –0.13 (1.06) | –0.14 (1.00) | 0.929 |
| Z-score of FEV1/FVC (n = 1809) | 0.01 (1.09) | 0.07 (1.05) | 0.230 |
| 15 years (post-bronchodilation measures) | |||
| FVC (L) (n = 2265) | 4.2 (0.9) | 3.3 (0.6) | <0.001 |
| FEV1 (L) (n = 2177) | 3.8 (0.8) | 3.1 (0.6) | <0.001 |
| FEF25–75 (L/s) (n = 2265) | 4.6 (1.2) | 4.0 (1.0) | <0.001 |
| FEV1/FVC (%) (n = 2177) | 91.1 (6.7) | 93.0 (6.3) | <0.001 |
| Z-score of FVC (n = 2080) | –0.90 (1.28) | –0.98 (1.30) | 0.186 |
| Z-score of FEV1 (n = 2001) | –0.38 (1.28) | –0.59 (1.36) | <0.001 |
| Z-score of FEF25–75 (n = 2080) | 0.14 (1.11) | 0.09 (1.20) | 0.300 |
| Z-score of FEV1/FVC (n = 2001) | 0.91 (1.13) | 0.77 (1.11) | 0.006 |
FEF25–75, forced expiratory flow at 25 and 75% of FVC; FEV1, volume expired in the first second; FVC, forced vital capacity; MVPA, moderate-to-vigorous physical activity, P25–P75, 25th and 75th percentiles; SD, standard deviation; Z-scores according to GLI-equations; –, not relevant.
Values are medians (25th–75th percentiles), means (SD) or absolute numbers (percentages).
P-value from the chi-squared test, Student’s t-test or the Mann–Whitney test comparing distributions across sexes.
Values in bold have P-values <0.05.
a
Number of children may vary because of missing information.
b
Highest parental social class.
c
Weight status defined according to body mass index Z-scores relative to UK 1990 population reference data.