What is a reason that these data may be unreliable?

It is information that is too old to be considered factual.

It was found on the American Cancer Society website, and websites are unreliable.

It is information that is used for a variety of purposes and not just gathered for research.

It is from a self-reporting survey, and teens may not want to answer the questions honestly.

It is from a self-reporting survey, and teens may not want to answer the questions honestly.

These statements can be reliable:

1. It is information that is too old to be considered factual.

This credibility and reliability of an information doesn't intend to how old it is. It just needs to be updated and revisited. This source may be outdated but every study has a significant implication to a certain populace however subjected to its own limitations.

2. It was found on the American Cancer Society website, and websites are unreliable.

Regardless of website or article, you should consider the authors of the website to have a clue if its reliable or not since the authors come from the ACS, this would entail that they have backed up researchers and studies to support their every claim. You can ask them the title and search for them yourself.

3. It is information that is used for a variety of purposes and not just gathered for research.

Yes but every assessment and test used for research should be specifically valid and reliable for the construct aimed to be measured, the content validity and the criterion-related validity, lastly also its reliability. Since the information was specified for the certain study then it is reliable and valid, therefore is reliable yet subject to its limits.