Meta analysis literature

Be sure to cite a reference for support from the peer reviewed literature (the text cannot be used). 

In Chapter 3 of the text, Chatburn describes a quantitative method of research known as a meta analysis. 
1) In your own words, a) define what a meta analysis is and b) what differentiates this design for other quantitative studies. 

2) How might a meta analysis give more clarity to a researched issue?  

3) Peruse the peer reviewed literature for a meta analysis research study. (You want the actual study, not an editorial, etc.)

    a) Give a brief summary of it and cite the source. 
    b) Give an example of one of the variables used in the study, including how it was measured and the level of measurement used (nominal, ordinal, interval, ratio).

    c) Were the results statistically significant?  What level of significance was used?

125-200 words; 25 words or less of directly quoted material. The response should demonstrate a thorough understanding of the topic, including critical analysis and references.  

Please answer the questions in number/list form to specify which answer is for which question. Please use this article: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4663397/pdf/WJH-7-2774.pdf