Particularly when associating outcomes with an activity you can be presented with a very long list that you must scroll up and down. Provide the ability to type part of the outcome name and have the list reduced to make finding the outcome(s) you are looking for easier.

Note that you must be able to search for one outcome, select it, search for a second outcome potentially hiding the first before selecting the second outcome. The hiding and showing due to the searching does not affect which outcomes are actually selected.