LibAnswers: Library answers

As an somewhat unscientific rule of thumb:

For Quantitative Research. Start with N3 (Objects, Names of technologies, Well researched and understood terminology)

For Qualitative Research. Start with N5 (Concepts, Feelings, Opinions)

If you test your search strategy, you might discover you need to increase this number to retrieve all your 'Gold Standard' sets of papers (If you are performing a Search Strategy Test). Review other systematic reviews in your field to see what the prevailing practice is, however, do not treat this as canon. This is a developing field in many disciplines so there is always room for improvement!