one-to-one merging when you want to combine one observation from each
data set, but it is not important to match observations. For example,
when merging an observation that contains a student's name, year,
and major with an observation that contains a date, time, and location
for a conference, it does not matter which student gets which time
slot. Therefore, a one-to-one merge is appropriate.
In cases where you must
merge certain observations, use a match-merge. For example, when merging
employee information from two different data sets, it is crucial that
you merge observations that relate to the same employee. Therefore,
you must use a match-merge.