Evidence in genealogy is any fact that ties a particular person to your family. Unfortunately, gathering evidence is a bit like putting together a complex 1000-piece jigsaw puzzle, often without parts of the picture printed on the pieces.
In today's world of the Internet, family genealogists, like yourself, can discover long-lost ancestors going back hundreds of years just by searching through databases or checking the information others have posted online. The percentage of evidence found this way is usually low. This is because those who post information online may not have proven that what they've posted is absolutely true.
Take the name of the person. If you think your ancestor is the only one with that name, think again. In my case, there's a second person living in town where I live with exactly the same name. At first glance, it would seem that that person could be me. It's only by further searching that you'll be able to tell us apart. This problem has caused legal and medical records problems already, so you can imagine the problems it will cause down the line when future generations search either one of us for their genealogies.
One way to corroborate a name is to check the location of the residence of the person. In the above case, even that can cause a problem. So in this case, you'd have to check the names of the person's parents to make sure you're on the right path.
Let's say that you've discovered a document or record providing information on an ancestor of yours. This information may have been included in a published genealogy, in which case it most likely would have been proven. But what if it came from an Internet site or a family tree submitted to an online registry? Or what if someone compiled some information on their family and shared it with you by E-mail. Perhaps this document is a will that names your ancestor as a beneficiary. Is it the original—most likely not—or is it a copy included in a published genealogy or a copy sent to you. Whatever the source, it's a piece of evidence—a piece of the puzzle. Now it's up to you to verify its authenticity.
To begin, determine the source's potential for accuracy. If the will is original, then it definitely is reliable. But if it's a copy, it may have been altered or forged. To prove the information is correct, you'll have to corroborate a fact in it using another source, perhaps a marriage or death certificate.
Does the will fit the time period for when it was written? Writing styles change over time. Compare this will with others of the same time period to see if it sounds right. You should be able to tell soon enough if it's the will your ancestor left. But if there are any discrepancies, you should be suspect.
Does this record provide enough evidence to support your supposition that you've made based on the limited resources at hand? If not, compare it with other records mentioning this person. Does it agree with them or does it contradict them and raise further doubts?
By following these steps, you'll have analyzed the evidence you've gathered. In this process, you take from that record as much information as you can possibly can about your ancestor, considering it both as an independent source and as one of a number of related sources. Are the facts within the record consistent? Do some things seem to have occurred at times not in keeping with the facts in the record? Often dates are wrong, causing a woman to give birth at an unrealistically early age. This could affect other information within the record. Could it be possible that the record, itself, was copied incorrectly or perhaps misunderstood if it were originally written in longhand? These are all questions you'll have to ask yourself as you peruse each new record.
Lastly, take a close look at the document, itself, and compare its contents with facts you've found in other records about this family, thus correlating the evidence you've gathered so far. Remember you're goal is to fit all the pieces of evidence together to accurately come up with a picture of your ancestor's life. Just as in a jigsaw puzzle, the pieces must fit exactly, or your picture will be distorted.