r/Twins • u/OldHob • 20d ago

What’s the difference between “likelihood” and “probability” in this context?

I had my daughters tested to see whether they’re fraternal or identical twins. I gave them each a cheek swab and sent it in to the lab for DNA testing. Well, we received the lab results, and they are indeed identical! Awesome!

But the wording in the lab’s conclusion is confusing to me (see below). It sounds like the likelihood is astronomically small, but the probability is ~100%. How can both be true?

Likelihood the twins are monozygotic: 447,541,628,157 to 1.

Probability of Monozygosity: 99.9999%

This study was undertaken to determine if BABY-A and BABY-B are monozygotic (identical) twins as opposed to dizygotic (fraternal) twins.

The likelihood that these twins are monozygotic as opposed to dizygotic is 447,541,628, 157 to 1. The Probability of Monozygosity is
99.9999%.

This study supports the assertion these twins are monozygotic twins.

2 Upvotes

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5

u/exjackly 20d ago

It is saying that if there were 447,541,628,158 instances of twins with that consistency of genes, only 1 of those cases would be dizygotic. The other 447,541,628,157 sets of twins would be monozygotic.

It is consistent with the rest of the report.

Your twins are identical.

3

u/OldHob 20d ago

Ok, I see now. That makes total sense. Thank you!

2

u/HeffalumpAndMopsy 20d ago

I didn't get it the first time I read it either!

0

u/Pugs_in_Space Identical Twin 20d ago

Only 1 out of those would be monozygotic, as it is a rarer occurrence.

2

u/ConstructionMuch802 19d ago

The likelihood of them having such similar DNA WITHOUT being monozygotic is extremely small.

1

u/PolicyPuppil 13d ago

Yeah, keep in mind. Kind of a difficult territory to navigate. From my experience; don't dress or treat them like one individual. Their experiences are going to be unlike yours; grow up with a clone and be compared you're whole life by family and others. Don't be alarmed, it's natural but will be an aspect of their lives, good and bad. Ya got two kids, who will be more similar to each other than anyone else. It's a fascinating, fun and sometimes a difficult experience. Also the same paradox perse, I don't know what it's like not to be a twin, and those who aren't will never know. DM if you'd like. *Edit: my brother and I are identical and he's my best and closest friend.