Credibility refers to the trustworthiness of the information. If the evidence you use is false, than any argument you make will also be false.
When looking at an information source, try asking yourself the Five W's.
Currency: the timeliness of the information
Relevance: the importance of the information for your needs
Authority: the source of the information
Accuracy: the reliability, truthfulness, and correctness of the content
Purpose: the reason the information exists
By scoring each category on a scale from 1 to 10 (1 = worst, 10=best possible) you can give each site a grade on a 50 point scale for how high quality it is!
45 - 50 Excellent | 40 - 44 Good | 35 - 39 Average | 30 - 34 Borderline Acceptable | Below 30 - Unacceptable
Be aware of your own biases, look at the credentials for the author, fact check.
Facts About Websites
Commercial websites (.com) may contain useful preliminary information, product information, and links to other websites. Remember that commercial sites are attempting to sell a product; therefore, the information may be biased.
Educational websites (.edu) are maintained by universities or other educational institutions. They are created with the idea of providing information that will be helpful for students and faculty. Usually, the webmaster has previewed the information and the links included. However, you should always evaluate these pages critically before using them. Be aware that student assignments and projects may be located on .edu sites.
Government websites (.gov) are provided by all departments of the Federal government. They contain a wealth of information on a wide variety of subjects. Government sites are also excellent sources of statistical information that is often easier to find electronically. Standard evaluation criteria should still apply.
Organizational websites (.org) are sponsored by non-profit entities. Most have good information and contain excellent links. Remember to evaluate each page on its own merits. Because many organizations have their own agendas, information from these sites may also be biased.
Country and state websites (example: .us or .ks) may have a two-letter domain name. These sites may have very useful information. However, all information should be evaluated.
Other domain names may be located in web addresses. Remember to use the same criteria to evaluate all sites.