If calculating coverage of your research subject sounds challenging, try using this coverage calculator! In my two previous posts about coverage, we talked about the concept of achieving better coverage of your research subject through gaining access to additional test results of their descendants. I talked about Paul Woodbury’s coverage formula and applied it to the Daniel Arnold case and Barsheba Tharp case. Read those posts here:
Get the Calculator
To use the calculator, click the link below and you’ll be taken to a “view only” version of the Google Sheet. To use it for your own calculations, click File > Make a Copy. The pop-up will ask which folder in your Google Drive you’d like to put the file. It also says “Apps Script file and functionality will also be copied, please review the attached script.” If you’d like to, you can click the attached Apps Script file called “DNA Coverage” and review the formulas. Otherwise, just click “Make a Copy,” and a new copy of the coverage calculator will open that you will be able to edit.
Access the coverage calculator here:
What is Coverage?
This calculator implements the Autosomal DNA Coverage Formulas shared by Paul Woodbury in the article “Covering Your Bases: Introduction to Autosomal DNA Coverage.” From that article: “Coverage refers to the amount of a research subject’s DNA that is represented in a DNA database through their combined tested descendants.”
Remember that a test taker’s coverage of their own DNA is 100% or 1.0. That same test taker provides 50% or 0.50 coverage for their parent. Two children of a parent will provide about 75% coverage of their parent.
How the Calculator Works
Within the calculator, Laura gives us the syntax for six functions/formulas to calculate coverage when you have 1, 2, 3, 4, 5, or 6 children of a research subject. The formulas are:
Laura includes the following instructions in the calculator about how to use the formulas:
- The formulas calculate the Autosomal DNA Coverage values for an ancestor using the coverage values of their children.
- Use the coverage formulas as you would other google sheet formulas. For example, to calculate the coverage for an ancestor with three children who are test-takers or have descendants who are test-takers, enter into a cell “= three_children(A10,B10,C10)”, where the coverage values for the three children are stored in the cells A10, B10, and C10.
- The code for the formulas can be found by selecting the “Script editor” in the Tools menu.
Examples in the Calculator
Laura has included several examples in the Google Sheet. The examples illustrate how the calculator works. Example 1 shows how to calculate the coverage if you have 1, 2, 3, 4, 5, or 6 children of the research subject. Example 2 shows the calculation of coverage by 1, 2, 3, 4, 5 or 6 grandchildren of the research subject, all with the same parent. Example 3 shows how you can compare the coverage that would be provided by three alternative test-taker options.
Example 3 is a wonderful illustration of how important it is to test independent descent lines of your research subject. Although we typically want to test the oldest generation, this example highlights how we also need to test descendants from different branches to increase coverage. In the example, the research subject had four children. Nine descendants of the research subject, through three of the children, have taken a DNA test, providing 55.6% coverage. You want to invite one more descendant to take a DNA test. Which one will provide the largest increase in coverage – a grandchild, a great-grandchild, or a great-great-grandchild of the research subject? The grandchild increases the coverage by the most, but the great-great-grandchild is the second best because they descend from an independent child line that doesn’t have any descendants tested yet. Be sure to view this example in the coverage calculator spreadsheet to see the details.
Laura included these notes about the examples:
- You can use the formulas and structure your spreadsheet however you’d like. You don’t need to use the particular structure or formatting of these examples.
- The branch for each child of the research subject is outlined in heavy black. Alternating branches are highlighted in light gray. All descendants within that box descend from that child.
- Each known test-taker is given a value of 1.00 (in green), as they provide 100% of their own DNA.
- In example 3, where you are reviewing three targeted testing options, each test-taker option is given a value of 1.00 (in yellow), as they would provide 100% of their own DNA.
- All other coverage values (in blue) are calculated.
- Click on the calculated coverage values (in blue) to see how the formulas are used.
- You can copy, paste, and edit the examples to match the scenarios you are working with.
Thank you to Laura Clark Murray for giving me permission to share this helpful tool! I hope you find it useful in calculating the coverage of your research subject and determining the best test takers to increase coverage in the future.