There's a wonderful book called Genealogical Evidence by Neal Stevenson -- I think it's must reading for anyone doing genealogical research. You might also check websites like ancestry.com, genealogy.com, or cyndislist.com -- I think they have sections you can click into that have how-to stuff, and might have something on judging evidence. To some extent, judging evidence is common sense. If you have an official birth record, for instance, that's primary evidence, but if you have a birth date that was given to you by, say, another researcher, but without any sources, that's much more questionable -- good researchers give sources. Census records, giving age at a certain time of year, would be better than sourceless material and are sometimes all you'll ever find, but census records aren't always accurate regarding age, so are not as good as an official birth record. But none of it is carved in stone -- even official records can be wrong, or different official records can conflict with each other. Stevenson says the best evidence of a birth date is testimony of the mother, because she was there when it happened and is, unless somehow impaired, the very best source. And the date of the source is all important. If you ask a mother when her child was born a year after it happened, she's likely to have it exactly right, but if you ask her 80 years later, it's possible that time and/or health may have fuzzed her memory. Or if someone in 1950 wrote down the date of something that happened in 1940, that may suggest personal knowledge of the event and would tend to be better evidence than someone in 1950 writing down something that happened in 1740 -- the latter would require additional source/sources to have any validity. It's like that. But if you can find the Stevenson book, it will answer all your questions. Good luck! Marilyn