Survey families or dataset series are data collection efforts that occurred over a period of time or in several geographic locations, using the same or very similar data collection methodology and instruments. Series may be multinational -- collected in more than one country -- or in a single country. Usually all the datasets in the series are collected with the support of the same institution or institutions, but individual surveys or datasets may have the support or assistance of additional parties. The advantage of series from a research perspective is that often data from a series are more easily comparable than data from a variety of sources.
A system is similar to a series in that they exist over a period of time and generally use the same or close to the same data collection instruments over that time period, such that the data are often more easily comparable. Systems of data collection may have no standardized output, or multiple standardized outputs, or the outputs may change significantly over time. For example, a civil registration system may have different standardized outputs for births, marriages, divorces, and deaths, or no standardized outputs at all.
In this new iteration of the GHDx, we intend to add more information about in-country data collection series and systems to create a more comprehensive overall picture of the data available for a country.