Additional file 1: Sample selection, county level prevalence and sequence typing data.
23 Zhejiang Province covers a population of 54.4 million, involving 90 counties, and in our sample system all of these counties were arranged by county HIV prevalence; the counties were divided into nine levels, each level with ten counties.
For the county-level analysis, total births and PTBs were aggregated from the study population set for each county and prevalence of PTBs/total births were constructed (n = 3141 counties).
These were summarised on a county-average level and compared to the county-average prevalence of observed Saf, Maf and Laf taken directly from the PND (using all the data for which full contact information was known, n = 662) using ArcGIS v.9.2 (ArcView®, ESRI, Redlands, CA, USA).
Complete list of variables is available in Additional file 2. Variable loadings are a function of the county-level prevalence of a variable and its association with the other variables contributing to the total county-level variability for a given domain.
Although waterpipe smoking is common in Gulf counties, its prevalence in Saudi Arabia is uncertain.
To assess implementation of California Senate Bill SB41 in two inland California counties where prevalence of injection drug use is among the highest in the nation.
County-level prevalence of PTB had a mean (standard deviation) of 10.42 % (4.12 %), with an interquartile range of 4.15%%.
We used county-level prevalence values of diagnosed diabetes for 2004 and 2005 created by the National Diabetes Surveillance System at the CDC (12).
We examine county-level prevalence of PTB in association with the EQI, as the EQI may reflect larger-scale exposure more appropriately than small scale or variable exposures, and to explore if there are drivers of county-level birth outcomes.
