Representativeness
A number of studies have been undertaken to assess the representative nature of the ALSPAC sample that was completing questionnaires or attending the Children in Focus clinic with (a) the total Avon area population, and (b) the whole of Great Britain, in 1991.
The population of parents and children living in the study area in 1970 were broadly similar to those of the rest of Great Britain. The 1991 census was used to compare the population of mothers with infants under 1 year of age resident in Avon with those in the whole of Britain. The results are shown below:
| Avon | Whole of Great Britain | |
|---|---|---|
| Owner Occupier | 68.7% | 63.4% |
| 1 + person/room | 26.0% | 30.8% |
| Car in household | 83.7% | 75.6% |
| Married couple | 71.7% | 71.8% |
| Non-white mother | 4.1% | 7.6% |
Thus the mothers of infants in Avon were slightly more likely than those in the rest of Britain to live in owner occupied accommodation, to have a car available to the household and to be less likely to have one or more persons per room and be non-white.
The comparison of the ALSPAC population completing questionnaires 8 months post-delivery with the whole eligible Avon population is shown below:
| ALSPAC | Avon | |
|---|---|---|
| Owner Occupier | 79.1% | 68.7% |
| 1 + person/room | 33.5% | 26.0% |
| Car in household | 90.8% | 83.7% |
| Married couple | 79.4% | 71.7% |
| Non-white mother | 2.2% | 4.1%% |
Thus, similar to all studies where a representative sample has been attempted, this study had a slight shortfall in the less affluent families (those living in rented accommodation, not having a car or being single or unmarried cohabiting). The study had a shortfall in ethnic minority mothers.
A comparison of the growth standards developed from the ALSPAC Children in Focus group with published national standards is shown below. Weights and birth lengths are in remarkable accord, and growth measures are very similar:
Measurements at birth, 1 and 2 year clinics: ALSPAC cohort vs. UK 1990 data
| Birth | 1 year clinic (mean age 1.03 yrs) | 2 year clinic (mean age 2.08 yrs) | |||||
|---|---|---|---|---|---|---|---|
| ALSPAC | UK 1990 | ALSPAC | UK 1990 | ALSPAC | UK 1990 | ||
| Male | |||||||
| weight (kg) | mean | 3.55 | 3.55 | 10.54 | 10.15 | 13.03 | 12.53 |
| sd range | 3.05-4.05 | 3.08-4.05 | 9.38-11.70 | 9.16-11.24 | 11.57-14.47 | 11.29-13.92 | |
| Length (cm) | mean | 51.26 | 51.09 | 76.53 | 76.23 | 87.54 | 87.82 |
| sd range | 49.31-53.21 | 49.07-53.11 | 74.08-78.98 | 73.66-78.75 | 84.60-90.48 | 84.57-91.04 | |
| Female | |||||||
| weight (kg) | mean | 3.42 | 3.41 | 9.84 | 9.73 | 12.42 | 12.29 |
| sd range | 2.99-3.87 | 2.96-3.87 | 8.83-10.85 | 8.79-10.77 | 11.11-13.67 | 11.06-13.70 | |
| Length (cm) | mean | 50.41 | 50.21 | 74.60 | 74.43 | 86.17 | 86.49 |
| sd range | 48.60-52.22 | 48.33-52.09 | 72.34-76.86 | 71.97-76.83 | 83.26-89.08 | 83.36-89.58 | |