This is a brief discussion of how
microsynth allows the user to aggregate outcome variables (passed to
match.out or match.out.min) over time, either
before or after matching, and how that can affect the workings of two
other arguments: period and start.pre.
microsynth will match treatment and control based on the variables
passed to match.out and match.out.min. But
there are two different ways to input parameters to
match.out, and they have different implications for how the
arguments work.
The simple way to pass variables to match.out is with a simple vector
of variable names (e.g., match.out=c("Y1", "Y2"). A more
complex way is to pass a list, containing a set of vectors with named
corresponding to variable names and elements corresponding to
instructions for how to aggregate those variables over time before
matching,
e.g. match.out = list('Y1' = c(1, 3, 3), 'Y2'= c(2,5,1)).
Under this specification, if the intervention occurs at time 10, then
matching will proceed across a) The value of Y1 at time 10; b) the sum
of Y1 across times 7, 8 and 9; c) the sum of Y1 across times 4, 5 and 6;
e) The sum of Y2 across times time 9 and 10; e) the sum of Y2 across
times 4, 5, 6, 7, and 8; f) the value of Y2 at time 3.
The choice between the simple and the complex input method is important, and it alters how other arguments work.
period specifies the granularity of the data used by
microsynth. When provided simple input from match.out (i.e., a vector of
variable names), period indicates that those variables
should be aggregated into the duration equal to the value of
period. E.g., if data are provided monthly and
period=3, then variables will be aggregated to the
year-quarter before matching. But when provided complex input from
match.out (i.e., a list of names and integers), then the user has
already manually specified how the variables should be aggregated prior
to matching; in this case, period will only affect the
appearance of charts and how results are reported (but not the matching
procedure).
start.pre is also affected. When match.out is provided
the simple input (a vector of variable names), start.pre will identify
the time of the beginning of the pre-intervention data to be used for
matching, plotting, and displaying results. Data observed any time
before the start.pre will be ignored entirely. If provided
the complex (list) input, then start.pre will merely affect
plotting behavior and suppress some of the results. But observations
before the start.pre will still be used for matching.
In conclusion, passing a list to match.out will lock
into place the parameters around the matching procedure; arguments such
as period and start.pre will only alter how
results are reported and how charts are plotted. But when
match.out is passed only variable names, then
period and start.pre will also govern the
matching procedure.