The goal of mirroring is to generate shared ancestor hints. Dan Edwards did not invent this technique and if you follow some of the Social Media groups like DNA Adoption, DNA Newbies, or Search Squad you will see this topic discussed often but it can be confusing. I have seen a lot of questions asking about why it works, how to set it up, how long to leave it before seeing results, the goals of the technique, etc. This article is written by Dan Edwards and his pdf is downloadable from his website.
From the blog page: “What we aim to accomplish in this post:
Provide definitions and an overview of methods for finding biological families of those who don’t know one or both biological parents, using tools at AncestryDNA.
Discuss possible future methods that may be helpful in reaching the same goals.”
The pdf file, titled “DNA Detective Work: Data Mining Through Mirroring and Maximizing Use of AncestryDNA” and covers the topic extremely well and uses numerous visual aids to show what he is explaining so that it is very clear and easy to follow. He goes through how to set it up, why do it, pitfalls and problems that might arise from doing it. Common errors that I often read about in discussion groups such as attaching your DNA to people that have been deceased for a long time is mentioned. Presumptions such as assuming you are related to both people instead of considering a “half” relationship is mentioned. For me, I had half-sisters and brothers and many generations back two first cousins had married, so you can’t have too many assumptions. I also have an adopted relative, so that further complicates results if you assume traditional relationships for everyone.
The post goes one to talk about some of the improvements that would be great to have on Ancestry.com. There are several great suggestions that would help everyone looking for family. In general, Ancestry needs more tools to match data sets such as DNA results and people in Ancestry trees. Ancestry does not provide a chromosome browser, but you can upload your DNA to GEDatch.com or FTDNA.com where you can use their chromosome browser. Mirroring to find your birth family is easy to do and well worth your time to explore. Ancestry continues to change the way their software works and continues to close some doors that allows techniques like mirroring, so if you are going to use the mirroring technique, I suggest you go ahead and get started before they change their policy to prohibit this.