Assess the quality of studies
Think of how CRAAP the text you are reading is!
CRAAP = Currency, Relevance, Authority, Accuracy, Purpose
How recent/old is your source? In certain fields it is very important that the sources are as recent as possible. In others, like history, a source or document from the past may be more valuable.
Is the text relevant to your dissertation? Does it help fill some section and answer your research question?
Who is the source of the information? Where was it published? Was it peer-reviewed?
What evidence is the source relying on? Is the evidence up to date? Is the evidence correctly interpreted? Is the argument made in the source logical? Is the methodology sound?
What's the purpose of the source? Is there an agenda? If it's a company report, it may try to portray the company in a positive light. If it's a government report, it may try to defend government policies.
In order to better evaluate a piece of work, you need to compare it with other sources dealing with the same topic(s). This is a main function of the literature review. Try to adopt a triple perspective:
For more information on the triple perspective and critical reading visit the Critical Reading Guide.