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Q. When I aggregate my data, there is no variable called "year" for the year. I only have variables "year_1", "year_2" and some others (year_mean, year_min, and year_max). What are these, and what should I use?

A. Once you select an aggregated data Set (i.e., where the unit of observation is not the group-year), there will always be multiple year variables because a single year variable cannot contain all of the information about the resulting observation. Instead, the "year_1" and "year_2" indicate the "first year" of the aggregation period, and the last year. So, if "year_1" is 1940, and "year_2" is 1941, then you have selected to aggregate to 2 year periods, and this particular observation covers 1940-1941. You should use these two variables.

Q. What are the variables that end with _mean, _min, and _max?

A. The _mean, _min, and _max variables are computed when you aggregate data by either time (to 2, 5, or 10 year intervals) or space (to states, regions, or the world). These variables report the mean, minimum, and maximum values across the aggregated observations for each variable in question. Because aggregated observations by definition contain information on multiple cases, a single variable (one variable reporting polity type, or level of protest, for instance) cannot contain all of the information about the underlying cases (group-years) aggregated to the final observation. Instead, for each variable from the MAR data Set selected by the user, these three variables will be computed and included in the output data Set. The computations take the mean, minimum, and maximum of the non-missing values on the variable across the groups. Missing cases are ignored in the computations.


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Last Updated June 20, 2016