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When we make misteaks…

The Legal Genealogist admits it.

It’s a consistent failing.

Even with a calculator at hand, I am mathematically challenged.

I joke about owning a complete one-for-every-day set of t-shirts reading: “I was an English major, you do the math.”1

And every so often … sigh … I prove just how challenged I can be.

Case in point: yesterday’s blog post. Where in the chart that accompanied the post I blithely asserted that since 12.5% was the expected amount of DNA inherited from a great grandparent, half of that would be 6.75%, and thus the expected amount of DNA inherited from a second great grandparent.2



math error

I still haven’t figured out how I made the mistake, but here’s the point: the instant a kind reader, Ken Kerr, called it to my attention, I fixed it. The post and the chart now online are correct: half of 12.5% is 6.25%

And whether it’s in a blog post, or in a family tree chart, when we make a mistake, we need to fix it.

When I was just getting started as a baby genealogist, I made every single mistake you can make. The book says my Bakers were from Boston? Sure! Except DNA said years later we were about as closely related to the Boston Bakers as to Adam and Eve… The census says that second youngest child was a girl? Fine! Until you realize the female Birdie was the male Bert. Same name same age same place — must be my guy, right? Until you figure out that every single male line in this family for 100 years gave at least one son the exact same name…

So… what do we do when we make a mistake?

We fix it.

Genealogically, our goal is to “reconstruct family histories or achieve genealogical goals that reflect historical reality as closely as possible”3 — to reach “accurate answers to research questions.”4

Sometimes that means correcting a mathematical mistake. Sometimes it means correcting a name or an age or a gender. And sometimes — as with my Bakers — it means lopping off whole branches of the family tree, and starting all over again.

It means — genealogically — ensuring that we have evidence to support our assertions. That we conduct reasonably exhaustive research into our question using the best available records. That we cite our sources. That we analyze and correlate the evidence we have found. That we resolve conflicts in the evidence. That we reach — and write up — our soundly reasoned conclusion.5

And when we make misteaks mistakes, it means we fix them.

With the help, occasionally, of a kind reader.

Cite/link to this post: Judy G. Russell, “12.5 divided by…,” The Legal Genealogist ( : posted 15 Mar 2021).


  1. In reality, I was a journalism major, but it’s close enough.
  2. Judy G. Russell, “Extrapolating from those numbers…,” The Legal Genealogist, posted 14 Mar 2021 ( : accessed 15 Mar 2021).
  3. Board for Certification of Genealogists, Genealogy Standards 2d ed. (Nashville, TN:, 2019), 1.
  4. Ibid. at 34, Standard 59, “Proved conclusions.”
  5. See “The Genealogical Proof Standard,” Chapter 1 in Genealogy Standards 2d ed., at 1-3.
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