Almost every tree that has been through more than one program has duplicates: two entries for the same person, each with part of the story. They are the most damaging kind of error because everything else is built on them. Charts split, evidence splits, and a descendant count of forty becomes sixty.

How they get in

• Merging two files that overlap. A cousin's tree and yours share great-grandparents; import one into the other and each shared ancestor appears twice unless the merge was done carefully.
• Accepting hints. Websites offer to add a person from a record. If that person is already in the tree under a slightly different spelling, there are now two.
• Re-entering. Great-aunt Mary was added years ago, forgotten, and added again from a different source.
• Shared trees. On FamilySearch and similar, other contributors may have created a second entry for someone already there.

How to spot them

GED-VIEW's Issues page lists likely duplicates: pairs of people with matching or near-matching names and birth years, and pairs of children in one family with the same name. That catches the obvious ones.

Tools > Find duplicates goes further and does the merging too. It proposes pairs of people who look like the same record entered twice, with a reason for each ("same full name", "same birth year", "same unique ID"), and it is strict on purpose: two people whose surnames, given names, birth years, death years or sex are both known and differ are never proposed, so twins and siblings born close together do not appear, and a placeholder name proves nothing. Sources, notes, media and repositories that are identical are found as well.

The People table catches the rest if sorted by surname and scanned. Two Mary Smiths born within a year of each other in the same county are worth a look. So is a family with two children of the same name, unless one died young and the name was reused, which happened a lot.

Comparing two candidates

Before deciding two entries are one person, open both profiles side by side and check:

• Do the parents match, or is one set missing? Two people with the same name and different parents are two people.
• Do the spouses and children match? Different families usually means different people. But watch for the same spouse under a maiden name in one entry and a married name in the other.
• Do the dates conflict, or does one just have less? A birth in 1852 versus "about 1850" is compatible. 1852 versus 1861 is not, unless one is clearly a typo.
• Where does each entry's evidence come from? If one has census citations and the other a family story, that tells you which to keep.

If it really is the same person, merge them with the Find duplicates tool: answer "The same person" on the pair, then decide, piece by piece, what record 1 (kept) takes from record 2 (a name, an event, a note, a citation; identical pieces need no decision). Every link that pointed at the absorbed record moves to the one kept, so families stay whole. Nothing is changed until you choose an ending: Download the file without the duplicates, Open it in the app as a new file, or Preview it on every page (the absorbed records in red, the kept ones in amber) and Accept. The original file is never modified. Or note the two IDs and merge them in the desktop program, if that is where the tree lives.

Next

Open Issues and look at the duplicate candidates, then run Find duplicates and read its pairs. Then sort the People table by surname and scroll one letter.