Start with characteristsics of the studies that you want to include, or have included, such as age groups, a defined outcome (e.g. diseas-free survival, cure rate, etc), double-blinded trials or not, length of the followup period, and others.  Which of these to select depends on your own research aims as well as having familiarity with the literature, and the disease you are looking at.

You can expect to find some difficulty in defining the results of some studies.  This is because some studies are simply not written up very well in the literature---they don't clearly state outcome measures, measurement techniques, selection methods and so forth.  It will help to make a table of the relevant characteristics you are looking at in these studies, such as what type of study(case-control, cohort, etc), how many subjects, main outcome measures, followup time, statistical methods and results.  As you begin to fill in this information about each study, an overall picture will begin to emerge.  

The above techniques are really for review of studies.  For a true meta-analysis, you usually want to pool the results, e.g., combine studies to get a larger sample size and combine the outcomes in a statistical way. But this only works if the outcomes are measured the same way.  The more divergent and non-similar the outcomes, measurements and other factors are, the less viable this technique becomes. Your meta-analysis may necessarily have to be made a bit vague or general when you combine several studies together.  For example, you might find that the drug shows a "40 to 60% improvement" over other treatment methods.

Thanks for ur assistance dr-jerry

Please let me k ow if these references/sites are useful to you:

1.  Avoiding Bias in Selecting Studies - Methods Guide for Effectiveness ...

https://www.ncbi.nlm.nih.gov › NCBI › Literature › Bookshelf

by M McDonagh - ‎2013 - ‎Cited by 9 - ‎Related articles

Feb 20, 2013 - In one meta-analysis, the conclusion was that the decrease in ... The inclusion or exclusion of a specific population can have a dramatic impact on ... One of the main goals in developing inclusion criteria is to minimize ambiguity. ..... / products/60/318/MethodsGuide _Prepublication-Draft _20120523.pdf.

2.  Developing the Review Question and Inclusion Criteria

https://alliedhealth.ceconnection.com/.../DevelopingtheReviewQuestionandInclusionC...Cached

by C Stern - ‎Cited by 28 

Inclusion Criteria. The first steps in conducting a systematic review. ... inclusion criteria are developed as a result of the question. .... tion (either for inclusion or exclusion criteria) must be delineated. .... ReviewersManual-2011.pdf. 5. Higgins  ...

Dennis

Dennis Mazur