A number of important characteristics of the registry are awaiting evaluation, including the utility to researchers of the minimum dataset, the representativeness of the population recruited to the registry and the cost per person recruited to studies through the registry.
None the less, the large dataset, the representativeness of the samples, the powerful nature of the children's outcomes, and the fact that data were collected originally for a different purpose improved the likelihood of the findings being valid.
Here's my two cents: all this debate about statistical representativeness, small datasets, only a handful of companies, and sites being chosen by the gas companies misses a key result -- perhaps the most important one.
Representativeness - A relevant concern for working on non-administrative data relates the representativeness of the dataset.
Even if good, rigorous research does eventually show that black women are rated differently, on average, in relevant characteristics (although it's highly unlikely considering the representativeness of this dataset), there may indeed be implications for racism.
Because including certain covariates significantly decreased the sample size (and the representativeness of the dataset), we developed a second model (data not shown) by adding drug resistance and clustering to the final model.
These weights are determined by expert judgment, based on the geographical level of detail and the representativeness of the datasets.
Nonetheless, most studies which focus on the effects of immigration on earnings are usually forced to use large cross-sectional data (Census, Labour Force Surveys) because large datasets are needed to guarantee representativeness of the immigrant population (see, for example, Chiswick and Miller, 2007 and Friedberg, 2000).
The main limitation of the present study relates to the representativeness of the datasets included.
In the R52 dataset we are exchanging accuracy for representativeness.
