Hello everybody! I'm Jarrett Ross the GeneaVlogger and...
"It's a quick genealogy tip!" On today's quick genealogy tip
i'll be discussing how the performance of ethnicity admixture percentages from
dna test results are measured. The ethnicity admixture
percentages and dna test results are what's known as a predictive system,
so basically it's just a system where they are predicting what your ethnicity
is. When we're discussing ethnicity admixture percentages
there are two main measurements of predictive systems that we use;
precision and recall. Precision is defined as a fraction of relevant
instances, or what's known as true positives,
out of the total retrieved instances, or what's known as the false positives
plus the true positives. So this is the actual equation for
figuring out precision. For recall it's defined as a
fraction of relevant instances, or true positives, out of the total
available instances, so that would be your false
negatives plus your true positives, and that
equation looks like this. Now i know that's probably really
confusing, so let's simplify it using some visuals. So here we see we
have 20 different objects and they are three different types of
shapes; we have circles, squares, and triangles. So if we're trying
to predict which shapes are circles and we choose
this selection, we have six circles. So for our precision what we're looking
at is the total number of circles that were actually chosen, which
is six, out of the total number of objects which
were chosen, that's ten. So for precision
we have 6 out of 10 in this predictive model.
But for recall what we're looking for is the number of relevant
instances that were chosen, so that's six circles,
out of the total available instances, so that would be
the total number of circles. So there were 12
total circles but only six were actually chosen, so that means that we have a
recall of six out of twelve. So when we're
discussing this idea with ancestry, instead of talking about circles, squares,
and triangles we're talking about specific population
groups - such as Native American, North African,
Western European. Now many of you may be asking "well,
how do i actually find this information?" and it's actually available
online. All you have to do is look up the dna testing companies'
white papers. There's only one of the main four companies that doesn't release
a white paper and that's MyHeritage but for 23andme, family tree dna, or
ancestry you can look up their white papers and
actually see the precision and recall numbers
for each of their population groups. So to explain a bit further
we're going to look at some actual precision and recall numbers
from 23andme's whitepaper. So let's start out by looking at the West
African for 23andme. For the precision it's 98 percent,
so what this means is that when they did their samples
98 percent of the time people who were assigned West African were actually West African,
and two percent of the time they didn't have
any actual West African ancestry. The recall for West African
is 93 percent so what that means is of all the people that were West African
only 93 of them were actually assigned West African.
So of all those who had West African, seven percent didn't get a reading
of West African in this sample. So let's take a look at some more
population groups to dive a bit deeper and we're going to look at one of the
most notorious in terms of admixtures and that's the French and German cluster.
So when we're looking at the french and german cluster on 23andme
the precision is at 83%. That means that in their sampling 17%
of the time people who were assigned french and german
had no actual proven French or German ancestry. For the recall on French
and German that was 28%, so that means that
if you have french or german ancestry - proven
french or german ancestry - there's only a 28% chance that this test
will actually pick that up. So last we're going to just
take a look at one more example of a population group
from 23andme and that's Vietnamese. So for the
Vietnamese on 23andme there's a 94 precision, so that means in their
sampling when they told people that they had
Vietnamese ancestry 94% of the time those people had proven
vietnamese ancestry. For the recall it's 79%,
so that means that in their sampling when they had people who
had actual vietnamese ancestry they were only assigned it
79% of the time. So 21% of the time people who had known and
proven Vietnamese ancestry were not assigned that. So for each
company I highly recommend reading into the
white paper as it also describes how they came to these actual precision
recall numbers, the actual sample numbers they used, and you
can often find references for their different population groups
as well as all sorts of different kinds of graphs and lots of other things to
really dive deep into understanding how they're
coming up with the results that they're actually giving you. Thank
you so much for checking out this quick genealogy tip!
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