Find drop out positions in a data.frame that contains multiple
questions that had been asked sequentially.
This function adds the Dropout Index variable do_idx to the data.frame which is necessary
for further analyses of dropout.
Use this function first to prepare your dropout analysis. Then, keep going by creating
the dropout statistics using compute_stats().
Details
Importantly, this function will start counting missing data at the end of the
data frame. Any missing data which is somewhere in between, i.e.
a single item that was skipped or forgotten will not be counted as dropout.
The function will identify sequences of missing data that go until the end of the
data frame and add the number of the last answered question in do_idx.
Therefore, the variables must be in the order that they were asked, otherwise analyses will not be valid.
See also
compute_stats() which is usually the next step for dropout analysis.