There is a lot of data out there, some of it easily findable and freely available via search engines, such as Google. Does that mean you can't use it? Not necessarily. Ask yourself a few questions to evaluate the data.
- Who? Who is supplying the data? Is the data producer considered an authority on the matter?
- Why? Why is the data being collected? What is the purpose? Is there incentive for bias (politics, influencing public opinion, lobbying)?
- When was the data collected? Is it current?
- How were the data collected?
Below are some categories of who and why.
- A Government Agency that collects the data as part of its mission (Centers for Disease Control, National Institutes of Health.)
- A Non Profit or Non Government Organization whose mission includes information and data about a topic or issue (Robert Wood Johnson Foundation, Kaiser Family Foundation)
- An Educational Institution, such as a research lab or institute
- A Researcher who collects data for scholarly research, as part of a lab, etc. (Data sources often described in the "methods" section of scholarly articles)
- A Private Firm? (Data like this often found in paid databases, such as Statista)
If the data you find helps answer your question, make a point and it meets one of the criteria above, it's should be OK to use. When in doubt, ask your professor!
For more information on finding health numbers, this section on Finding Health Statistics from the NIH/National Library of Medicine may be helpful