Reviewing historical data is a significant part of researching your family history. In the not so distant past, this involved finding and reading historical documents. Luckily for genealogists today, a huge amount of historical documents have been digitized meaning you can now find and review documents online.
While this makes finding historic documents about your family members much easier - it can be done from almost anywhere that there is an internet connection - it is not a magic bullet; the documents still need to be carefully reviewed for accuracy in order to avoid making mistakes with the information that you load into your family tree.
Did you know that most documents are translated by volunteers? Census records, church records, government documents - all of these are reviewed and the information is then translated and put online. However, not all records are translated correctly, and this is where problems can arise.
I use several different sources for reviewing and adding historical documents to the myriad of people that are documented in my family tree. One of the sources that I have found to be the best source of said documents is Ancestry.com. While not free, a WorldWide Explorer subscription gives members access to digitized records from a number of countries. In my case, the majority of my ancestors and living relatives are located in Canada, the USA, Great Britain, Australia and New Zealand so this membership suits me well.
These historic documents come up as "hints" on Ancestry and each document will list the source of the information and a summary of the information that is contained in the document, such as names, date of birth, marriage date, death date, etc. You can also click on the image of the document (if there is one - most documents have actual images of the original document) and review the data for yourself. In the case of census records, the majority of the information available was captured by hand, either in cursive (handwriting) or printed. More often than not, the information is in cursive. Depending on how nice the original census taker's handwriting was, the written words on the documents can either be very clear and easy to read, or, as in the case of my own handwriting, as difficult to read as a doctor's quickly scribbled prescription!
In rare cases where the translator is not sure of the word or words being translated, they will make their uncertainty clear by indicating such on the translated copy, either by use of a question mark or by stating something like "Marcy or Mercy" if they are uncertain about the actual name/date, etc. With most translations that I have seen however, the translator just puts in the word that they think it should be, and the word they choose does not make sense, especially when compared to the same name/date, etc. on corresponding records.
In order to minimize mistakes being made in my own family tree, I try to be absolutely certain that the data I am entering is correct. To do this I try to match the data with previously data I have found, and if there is a significant difference in the data, I will open the picture of the document and read the original document myself. This usually solves the problem with a translation error, but if it does not, I simply mark the hint as "undecided" so that I can save it for review at a later date when I hopefully have more data to compare it with.
For this same reason, I rarely (if ever) directly merge other member's family tree information into my own family tree. In the past I have had many issues with combining another member's family tree with my own, and I literally had to spend hours undoing the misinformation and removing it from my tree. That's not to say that other members family tree information is not valid, but I find it safer to verify their information first, and then manually enter the information into my own family tree. It is much easier to put the correct information into your family tree the first time than it is to try and remove the incorrect information at a later date.
So go ahead and use the online data that is readily available such as census records, birth records, death certificates, cemetery records, etc. and use this valuable data to build a strong picture of your ancestors, but remember to double-check the data first, and if it doesn't make sense, hold off on using it until you can verify that the information is correct. You'll be glad that you did!