Elvis had a twin brother (who died at birth).

Historically, approximately 1/125 of all births were fraternal twins and 1/300 were identical twins. The probability that Elvis was an identical twin is approximately . . .

5/11, or 45%.

Posted by Andrew on 3 January 2005, 6:36 pm

Elvis had a twin brother (who died at birth).

Historically, approximately 1/125 of all births were fraternal twins and 1/300 were identical twins. The probability that Elvis was an identical twin is approximately . . .

5/11, or 45%.

## Recent Comments

- Martha on Can talk therapy halve the rate of cancer recurrence? How to think about the statistical significance of this finding? Is it just another example of the garden of forking paths?
- Andrew on Creativity is the ability to see relationships where none exist
- Chris G on Creativity is the ability to see relationships where none exist
- Andrew on Creativity is the ability to see relationships where none exist
- Chris G on Creativity is the ability to see relationships where none exist
- Andrew on Can talk therapy halve the rate of cancer recurrence? How to think about the statistical significance of this finding? Is it just another example of the garden of forking paths?
- Alex F on Can talk therapy halve the rate of cancer recurrence? How to think about the statistical significance of this finding? Is it just another example of the garden of forking paths?
- Corey on John Lott as possible template for future career of “Bruno” Lacour
- Dan Wright on John Lott as possible template for future career of “Bruno” Lacour
- Andrew on John Lott as possible template for future career of “Bruno” Lacour
- jrc on John Lott as possible template for future career of “Bruno” Lacour
- Oncodoc on Can talk therapy halve the rate of cancer recurrence? How to think about the statistical significance of this finding? Is it just another example of the garden of forking paths?
- D.O. on Creativity is the ability to see relationships where none exist
- Steve Laniel on John Lott as possible template for future career of “Bruno” Lacour
- Anonymous on Creativity is the ability to see relationships where none exist
- D.O. on John Lott as possible template for future career of “Bruno” Lacour
- Martha on Can talk therapy halve the rate of cancer recurrence? How to think about the statistical significance of this finding? Is it just another example of the garden of forking paths?
- Martha on Can talk therapy halve the rate of cancer recurrence? How to think about the statistical significance of this finding? Is it just another example of the garden of forking paths?
- Andrew on Creativity is the ability to see relationships where none exist
- Martha on Creativity is the ability to see relationships where none exist

## Categories

Isn't it (1/300) / (1/125 + 1/300) = 5/17 ~ .29?

No, it's 5/11. See http://www.stat.columbia.edu/~gelman/book/ and go to the solutions to exercises in the second edition, Exercise 1.6.

Here's how I think of it:

In 3000 births, we would expect 3000/300 = 10 sets of identical twins. Roughly half of those we would expect to be boys. That's 5 sets of boy-boy identical twins.

In 3000 births, we would expect 3000/125 = 24 sets of fraternal twins. One fourth would be boy-boy, one-fourth would be girl-girl, one fourth would be boy-girl, and one fourth girl-boy. Therefore six sets would be boy-boy.

So, out of 3000 births, five out of eleven sets of boy-boy twins would be identical. Therefore the chances that Elvis was an identical twin is about 5/11.