Estimating Neighbourhood-Level Socio-Economic Effect on Preterm Births Using a Multilevel Approach: A Case Study in Georgia, USA

This study investigates the contextual effect of neighbourhood socio-economic status (SES) on the risk of preterm birth (PTB) using multilevel models. Birth data retrieved from 2000 Georgia Vital Records were geocoded and joined to their respective census tracts. The census tract level Index of Deprivation (IoD) was calculated using nine 2000 Census variables based on a previously proposed 'standard' index. Two-level random intercept regression models were developed using 117,329 live and singleton births at the individual level and 1618 census tracts at the neighbourhood level. After adjustment for individual-level factors, IoD generated an odds ratio of 1.006 (95% CI 1.00-1.01), showing a modest but significant effect on PTB. Intra-class correlation (ICC) was 0.83% after adjusting for individual-level factors and the census tract level IoD. A wide IOR-80% interval (0.74-1.36) suggests large unexplained residual in between census tract variation remained. The median odds ratio (MOR) value of 1.17 revealed that the unmodelled neighbourhood effect was stronger than the fixed effect of census tract-level predicting variable, IoD, but weaker than the effects of several individual-level predictor variables, including race, tobacco use, prenatal care, foetal death history and marital status. Overall, better census tract-level SES would have a modest protective effect for PTB risk. The full strength of multilevel models should be exploited further to help our understanding of PTB aetiology.