What about duplicate entries in family trees?

A family tree is a branching structure that treats each marriage (or the equivalent) as a node starting two (or more depending on the number of marriages) separate branches. Genealogists approximate this structure with a pedigree chart. However, the analogy between a living tree and a pedigree is incomplete. All real families are more complex than the simple branching indicated by either a tree by analogy or a pedigree chart. The family tree model is derived from viewing ancestry from a strictly biological basis. Representations of family trees as a branching structure date back hundreds (if not thousands) of years. Here is a sample from the 16th Century.

The family tree of Ludwig Herzog von Württemberg (ruled 1568–1593)

For the past few years, digital representations of the tree structure have multiplied across the Internet. The basic idea of a graphical representation of relationships has now spread to millions of online family trees. The rather simple concept of pedigree collapse, the concept that people end up marrying their cousins, guarantees that there will be duplicate entries between family trees for separate individuals. For example, if I have a family tree and one of my first cousins also has a family tree, then we will share all of the related family lines. If we have our family trees on the same online program, such as Ancestry.com or MyHeritage.com, then there will be a huge number of duplicate entries between the two trees. A program such as the FamilySearch.org Family Tree tries to eliminate duplicates in the Family Tree by having one, unified family tree.

What is more serious than the mere duplication of individuals between family trees, is the problem of duplicates within one family tree. With the FamilySearch.org Family Tree, the challenge of internal duplicates is still an overwhelming issue. In fact, the tree structure and data have yet to be completed to the point where some duplicates can be resolved. Here are some articles on the subject of duplicates in the FamilySearch.org Family Tree.

Hanna, Karen. “Duplicates in FamilySearch’s Family Tree: Why They’re There, How to Find Them, and How to Resolve Them.” FamilySearch Blog, August 6, 2014. https://familysearch.org/blog/en/duplicates-familysearchs-family-tree-theyre-find-resolve/.

Tanner, James. “Rejoice, and Be Exceeding Glad...: Merge Obvious Duplicates in the FamilySearch Family Tree.” Rejoice, and Be Exceeding Glad..., November 29, 2015. http://rejoiceandbeexceedingglad.blogspot.com/2015/11/merge-obvious-duplicates-in.html.

———. “Rejoice, and Be Exceeding Glad...: Observations on Duplicate Entries in the FamilySearch Family Tree.” Rejoice, and Be Exceeding Glad..., September 6, 2015. http://rejoiceandbeexceedingglad.blogspot.com/2015/09/observations-on-duplicate-entries-in.html.

———. “Rejoice, and Be Exceeding Glad...: The Issue of Duplicates in FamilySearch Family Tree.” Rejoice, and Be Exceeding Glad..., May 4, 2015. http://rejoiceandbeexceedingglad.blogspot.com/2015/05/the-issue-of-duplicates-in-familysearch.html.

———. “Rejoice, and Be Exceeding Glad...: Where Are the Duplicates in FamilySearch.org Family Tree?” Rejoice, and Be Exceeding Glad..., January 30, 2015. http://rejoiceandbeexceedingglad.blogspot.com/2015/01/where-are-duplicates-in-familysearchorg.html.

“The Ancestry Insider: Merging People in FamilySearch’s Family Tree.” Accessed January 23, 2016. http://www.ancestryinsider.org/2013/09/merging-people-in-familysearchs-family.html.

Many of the duplicate entries in the FamilySearch.org Family Tree date back to origins of the program because of the combined databases used to seed the original information in the tree. There is a much less serious issue with duplicates within a singe family tree in websites such as Ancestry.com and MyHeritage.com because they both check for duplicates at the time an entry is made and both have mechanisms for merging or deleting duplicate entries. 

There are essentially three ways to deal with duplicate entries within the same family tree. They are as follows:

• Combining records -- Combining allows all of the existing information in the duplicate records to be preserved. It also allows the records to be later separated if the combined records turn out to be wrongly combined. But in some cases, such as happened with the new.FamilySearch.org program, combined records created more problems than solutions. 
• Merging duplicate records -- Merged records solve many of the problems generated by combining records, but create the potential for loss of information unless all of the information from the merged records is preserved. If records are merged, then there is a surviving record that may have a different set of relationships than are in the previously separate records. 
• Deleting duplicate entries -- This solution addresses the immediate problem of the duplicate entries but runs the risk of losing the deleted information and the deleted relationships. 

Each of these methods of dealing with duplicates has its advocates. Here are some articles that talk about how to deal with duplicate entries in Ancestry.com and MyHeritage.com.

Ancestry.com

Member Trees: Merge Duplicate People from Ancestry.com

Merging Duplicate Individuals in an Ancestry Member Tree

How to Delete and Merge Duplicates in Ancestry Family Tree

MyHeritage.com

Here is the information about MyHeritage.com's family trees from the Help Center.

How do I merge duplicates in my online tree?
It is not possible to merge duplicate person cards. If one of the individuals in your tree has been entered in two places, you can delete one person card and keep the second person card with the help of the attach/detach feature. 

These are the steps you need to take, if a certain individual was entered twice into the tree: 

1. Find the person who appears twice in the tree, and open his/her card with the least amount of information. 

2. Remove connections between this card and other family members in the tree as described in the related article, until it’s left alone. 

3. Delete this card, by clicking on the ‘More’ button on the left side panel, and choosing ‘Delete this person’. 

4. Go to the remaining card of this individual, and connect him/her to all the individuals that were disconnected from the deleted card. 

Please use the following FAQ article for the detailed instructions on how to remove connection and connect individuals in your family tree online: How can I attach / detach existing people in my online family tree? 

Note: a person’s card may appear twice because of cyclical relations inside the tree, but in that case there will be an ‘x2 icon’ next to him, meaning the data is NOT duplicated.

You can see that each of the programs has chosen to handle duplicate entries in different ways. Duplicates are not as serious a problem in Ancestry.com and MyHeritage.com because the duplicates come from your own actions. If there are duplicates in these programs, it is due to your entering them.