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 (e.g. Environmental Protection Agency, NOAA, United Nations, etc.)
- A Non Profit or Non Government Organization whose mission includes information and data about a topic or issue
- 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 should be OK to use. When in doubt, ask your professor!