Throughout your research it is of utmost importance to define and understand your specific outcome(s) of interest. In other words, you should clearly define what you want to measure, i.e. the outcome or construct of interest. This outcome should be clearly defined, so you are able to select an appropriate outcome measurement instrument measuring the specific outcome, judge whether the items, task, observations or parameters of an outcome measurement instrument are relevant for the outcome, and whether the outcome is comprehensively covered by the items/task/observations/parameters.

Others should be able to understand what you want to measure. Just a word describing the outcome of interest may not be enough.

You are deciding on the most suitable outcome measurement instrument for your study. This decision should be based on the evidence of the quality of available outcome measures (i.e. reliability and validity), as well as on aspects of feasibility. A high-quality performed systematic review on outcome measures gives you a clear overview of all important aspects to make your choice.

You want to conduct a systematic review of outcome measurement instruments in which you want to provide an overview of all evidence of important quality aspects of outcome measurement instruments that all measure a specific outcome.  Such reviews are extremely useful for selecting the most suitable outcome measurement instrument at the moment.