If I may ask a question, when undertaking the study selection process and abstracts and titles are initially screened by reviewers/ For example if pub med is searched ( for an RCT systematic review) electronically and on the prisma flow chart it states 163 were initially were screened and after the abstracts were 155 were excluded prior to abstract review. My question is what does the 163 mean ?. Does this include any paper related to the subject ie. conference reports, other systematic reviews, observational studies, case reports etc?.Any thoughts ?

Includes all citations thrown up by search.

have a look at the PRISMA statement for full details.

Any paper the search produced. Publication type depends on their search strategy - if the search engine allows for filtering out certain types, and the authors decided to do that, then those will not feature in the results, or in very small numbers.

You need to check their search strategy to find out.

Is it possible to obtain online a couple of MSc level dissertations (samples-pdf's) in medicine for review as to the depth required