Because our study was a convenience sample, there is also the potential for selection bias and inclusion bias.
First, because our study was single-center and prospective, the sample size was modest and may limit our conclusions.
Mortality was not associated with compliance, possibly because our study was underpowered to establish such a relationship.
Because our study was focused in the central part of coastal Maine, we recalculated this subsidy including only counties in central Maine (Hancock, Knox, Lincoln, Sagadahoc, and Waldo).
Because our study was ecological in nature, we could not identify the specific reasons for the observed differences in prenatal care between our two income groups.
We decided to proceed in this way because our study was exploratory.
Second, because our study was cross-sectional study, reverse causation could affect the results.
Because our study was conducted as a public health response, it has the following limitations.
Because our study was observational in nature, no causal relationships can be deduced from our findings.
Because our study was based on pseudonymous data, we did not have to obtain informed consent.
Because our study was conducted within a fairly homogeneous Chinese population, we had limited generalizability.
