Finding & Using Data or Statistics
Whether you are looking for a simple statistic to give some context in your research paper or more detailed data for analysis, all data and statistics you might find need to be considered critically. Data on religious affiliation is typically gathered either from individuals or from organizations. Sources for data gathered from individuals (such as the Census, American Community Survey, or Statistical Abstract of the United States) tend to be more accurate, but less detailed than data gathered from organizations. For example, data from the Statistical Abstract may have 33 different denomination categories for "Christian," but may only use one category for "Jewish." Data reported by organizations is not always bound by these categories, but because it relies on self-report by the organizations, there is a tendency to over-report membership numbers. Always keep the source of your data or statistics in mind, particularly when comparing numbers from two different sources.
Doing ethnographic research? This is a great place to find guidelines and best practices.