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Simplified Probability Model

This page presents another model for interpreting Y-DNA matches. We call it the "Janzen Model" because its concept comes from a post to Rootsweb's DNA-Genealogy-L mailing list by Tim Jantzen on 22 Aug 2009. While less precise than the model we've presented elsewhere, it greatly simplifies the process of interpretation.

Precepts

We will limit both our time window of concern and the probability gradations:

Matrix

Here's our matrix, using cumulative probabilities for a normal curve. This quantification defines specifically what we mean when we apply the subjective terms.

Simplified Probability Matrix

Highly
probable 
Probable Possible Unlikely Very
unlikely
Probability (%) t 90% to100% 68% to 90% 32% to 68% 10% to 32% 0% to 10%
S.D. (sigma)
from the mean
> +1.54σ +1.0σ to +1.54σ -1.0σ to +1.0σ -1σ to -1.29σ < -1.29σ
Interpretation  0 to 1/10
CMA outside
the window
1/10 to ~1/3
CMA outside
window
1/3 to 2/3
CMA outside
window
2/3 to 9/10
CMA outside
window
9/10 to 1/1
CMA outside
window

How it works

Always use the maximum number of markers that can be compared. A match on 37 markers may also be reported with the same person at 25 markers and 67. In this instance, use the 67; it is more reliable.

We'll transfer the cumulative probabilities to decision-making matrix tables for various time frames:

Note: 111 marker matches are not included in the tables below due to the newness of the tests.

~650 Year Window

This is the time window used by Taylor Family Genes to declare matches. It represents an estimated 55 transmission events across both compared lines since roughly 1350 CE, the beginning of common surname adoption. The researcher may have difficulty finding records pre-1500 to identify the common ancestor.

Probability Table 1: ~650 years, 55 TE

Genetic
distance
12
markers
25
markers
37
markers
67
markers
0 Probable
73%
Highly
probable

96%
Highly
probable

>98%
Highly
probable

>99%
1 Unlikely
36%
Probable
82%
Highly
probable

>98%
Highly
probable

>99%
2 Unlikely
12%
Possible
59%
Highly
probable

96%
Highly
probable

>98%
3 Very
Unlikely

3%
Possible
35%
Probable
89%
Highly
probable

>98%
4 Very
Unlikely

0.5%
Unlikely
17%
Probable
76%
Highly
probable

97%
5 Very
Unlikely

~0%
Very
unlikely

7%
Possible
60%
Highly
probable

93%
6 Very
Unlikely
~
0%
Very
unlikely

2%
Possible
43%
Probable
87%
7 Very
unlikely

~0%
Very
unlikely

<1%
Unlikely
27%
Probable
76%
8 Very
unlikely

~0%
Very
unlikely

<1%
Unlikely
15%
Possible
64%

Genetic distance means the number of mismatching markers plus, for some markers, the number of steps by which the markers disagree. It measures the estimated number of mutations.


~500 Year Window

Estimated 40 transmission events across both compared lines, since roughly 1500 CE. Some researchers prefer this shorter window due to scarcity of available records before 1500.

Probability Table 2: ~500 years, 40 TE

Genetic
Distance
12
markers
25
markers
37
markers
67
markers
0 Possible
62%
Probable
90%
Highly
probable

>98%
Highly
probable

>98%
1 Unlikely
24%
Possible
66%
Highly
probable

96%
Highly
probable

>98%
2 Very
Unlikely

6%
Possible
39%
Probable
86%
Highly
probable

97.7%
3 Very
Unlikely
1%
Unlikely
18%
Probable
70%
Highly
probable

93.8%
4 Very
Unlikely
0.1%
Very
unlikely

7%
Possible
50%
Probable
86%
5 Very
Unlikely
~0%
Very
unlikely

2%
Unlikely
31%
Probable
74%
6 Very
Unlikely
~0%
Very
unlikely

0.5%
Unlikely
17%
Possible
57%
7 Very
unlikely

~0%
Very
unlikely

0.1%
Very
unlikely

8%
Possible
43%

~250 Year Window

Estimated 16 transmission events across both compared lines since roughly 1750 CE. This table is not recommended, because the window is shorter than the estimated frequency of some mutations.

Probability Table 3: ~250 years, 16 TE

Genetic
distance
12
markers
25
markers
37
markers
67
markers
0 Unlikely
32%
Probable
73%
Probable
86%
Highly
probable

97%
1 Very
Unlikely

6%
Possible
38%
Possible
59.
Probable
88%
2 Very
Unlikely

0.6%
Unlikely
14%
Unlikely
31%
Probable
70%
3 Very
Unlikely

~0%
Very
Unlikely

4.1%
Unlikely
13%
Possible
48%
4 Very
Unlikely
~0%
Very
Unlikely

0.2%
Very
unlikely

4%
Unlikely
28%
5 Very
Unlikely
~0%
Very
unlikely

~0%
Very
unlikely

1%
Unlikely
14%
6 Very
Unlikely
~0%
Very
unlikely

~0%
Very
unlikely

0.3%
Very
unlikely

6%
7 Very
unlikely

~0%
Very
unlikely

~0%
Very
unlikely

~0%
Very
unlikely

1%

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Revised: 6/292011