Once one gets so far back in their tree, one finds ancestors in common with other researchers. It is all too tempting to collect information by copy and paste information from another researcher's tree, but this becomes a problem if you find the link was in error or the research inaccurate at a later date.
How should one take advantage of information in another's tree without making a verbatim copy that soon becomes difficult to manage?
Always cite your sources!
I often add the info to my tree, citing the place where I'm taking it from as a source, and setting my confidence in the source to "Very Low". (Most systems I've seen have a way to flag the confidence of a source citation -- Gramps, for example, goes from "Very Low" to "Very High".)
I usually later find that these are good clues about where to research further -- i.e. what to search for in more reliable databases. When I find better evidence, I can add a new citation (with a higher confidence rating) to that better source.
This is especially true if the author of the "Very Low" confidence source that I'm citing has done a decent job of citing sources.
However, if the tree I'm looking at is sloppy -- no sources, obvious errors/misspellings, generations out of place, etc -- I don't bother taking any of the info down.
You can treat this just as you would (for example) Aunt Gertie's insistence that her great grandmother was a noblewoman. It is a knowledge claim (or an assertion) that is not yet backed up by evidence. Either one provides you with a starting point for further investigation that may shatter the myth or provide some confirmation.
It is useful to copy (or better still, to summarise) the data from the possible cousin's tree into your working journal and then to move parts of it into your tree when (or if) you are able to locate (and cite) supporting evidence.
Of course, if the on-line tree has actually listed sources, you have a head-start on checking the claims. But do not simply accept the claims at face value.
I believe the correct methodology should be to keep your research separate from others. Do not merge other people's data into yours. Only add information to your tree that you have personally verified.
Ideally, we'll want genealogy programs that can "virtually merge" two datasets together. Some online trees work this way. I'm not sure if any desktop programs can do this yet.
Desktop programs tend to have merge programs in them that help you merge other people's data into your own. I think this is a disservice and is promoting a bad thing.
The four advantages of keeping the data separate are:
No time wasted in copying/merging the data.
You can instantly update the dataset when you get an updated file from the other researcher. Just replace the old one with the new one.
You know everything in your own dataset is your own research, and you can trust it.
You know if you send your dataset to anyone, it is your own work and you can stand behind it.
Before accepting any particular claim from someone else's tree, you should examine the source(s) they reference for that claim. Only after you have verified that the claim is supported by reliable sources should you add the claim to your own database, and always add the source reference(s) to your database as well. It should go without saying that online trees and GEDCOM files are not of themselves reliable sources and should not be used as such.
While I might copy info from another tree, it would not be into my tree that I pasted it. I maintain a research folder on each person of interest and that is where I would paste the info. Once I have 'completed' verifying the info, I then enter the info into my tree along with the sources used to verify the info.
I still add the info to my tree but will make a note that it is probably wrong.
I think most of my suggestions have already been covered in some depth here. Sometimes I include a limited piece of information with a status of 'questionable' or 'unsubstantiated', and a citation to that researcher's tree or data. I use this mainly for trees from researchers that I know have put some effort into their work. In those cases where there may be very suspect larger-scale parts of someone's tree then I use the other suggestion of copying to a research folder for further analysis. This avoids cluttering my tree with large amounts of suspect linkage.
The only potentially interesting thing I have to add is that a lack of citations or reasoning on a published tree may or may not imply a poor quality tree. This depends to a large extend on the willingness to share that level of detail by the author. Without cited sources then you're basically sharing conclusions only, and you may have heard the term "conclusion sharing" from some content providers. In my personal opinion, sharing citations is good, but sharing the reasoning behind your conclusions is more controversial since that where most of the time, effort, and expense will have gone. Unfortunately, it would appear many content providers have given scant support and encouragement to adding those citations.
You can use it as hints for areas to research next. Just don't add the information until you are able to corroborate it.
Wile I agree with Louis Kessler that as far as is practical it is best to keep family trees in separate files (I am a fan of Louis' Behold software which is an excellent way to display multiple trees whilst not destroying their individual integrity). However, there are a number of reasons why I also attempt to merge gedcoms from different sources.
My main genealogy database is Legacy - it has a fairly good merging procedure which is basically an aid that allows you to visually compare suspected matches; if you are careful it works well but it is very time consuming if you are merging a lot of records.
I am also a member of My Heritage which features 'SmartMatching' - which is another tedious process that is based online matching which enables you to confirm or reject suggested matches. The big advantage of this process is that the accuracy of your database is gradually improved and to share those improvements with your main, offline, database once a year you need to download the My Heritage gedcom and merge it into the original sitting on your computer. Note: I also belong to Geni (which has just been acquired by My Heritage - you can export a gedcom from Geni but it has the probelms thata many desktop programs can't import it, let alone merge it).
The best merging program I have found is GenMerge and I now routinely export my gedcom from Legacy and merge it with the latest export from My Heritage. Once I am am happy with the merged gedcom, I use it to update sites like My Heritage, Ancestry and Genes Reunited another online service that reports (hot)matches with records in other users trees.
Regards
