[...] * A key concern with many Big Data sources is the selectivity, (or conversely, the representativeness) of the dataset. A dataset that is highly unrepresentative may nonetheless be useable for some purposes but inadequate for others. Related to this issue is the whether there exists the ability to calibrate the dataset or perform external validity checks using reference datasets. Selectivity indicators developed for survey data can usually be used to measure how the information available on the Big Data Source differs from the information for the in-scope population.