What is the Probability of 4 Out of 5 Recent US Presidents Being Left-Handed?

  • Context: Undergrad 
  • Thread starter Thread starter Pumblechook
  • Start date Start date
  • Tags Tags
    Probability
Click For Summary

Discussion Overview

The discussion centers on the probability of 4 out of 5 recent US Presidents being left-handed, considering the general population's left-handedness rate. Participants explore various probabilistic models and the implications of the sample size of US Presidents.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates the probability of 4 out of 5 recent Presidents being left-handed as 0.00045, using a model based on the left-handed population rate.
  • Another participant argues that there is no improbability against a skewed tendency in such a small sample size of Presidents.
  • A different participant agrees with the initial probability calculation but suggests that the total number of Presidents (43) is irrelevant to the specific probability of 4 out of 5 being left-handed.
  • One participant counters that the larger number of Presidents increases the likelihood of observing a sequence of 4 out of 5 left-handed individuals, proposing a need to consider all combinations of left- and right-handed Presidents.
  • Another participant introduces the concept of runs in a sequence of Bernoulli trials, questioning the independence of the trials due to Presidents serving multiple terms, while suggesting a reduction of the problem to individual Presidents to address dependence.
  • One participant expresses a sentiment of finding the situation interesting but ultimately questions its significance.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the relevance of the total number of Presidents to the probability calculation and the implications of independence in the context of multiple terms served by Presidents. No consensus is reached on these points.

Contextual Notes

Participants note the potential complexity of calculating probabilities due to the small sample size and the nature of the trials, including considerations of independence and the need for comprehensive combinations of outcomes.

Who May Find This Useful

This discussion may be of interest to those exploring probability theory, statistical reasoning, or the implications of sample sizes in probabilistic models.

Pumblechook
Messages
359
Reaction score
0
4 out of 5 recent US Presidents have been left handers? Given that 1 in 10 of the population is left handed what is the probability of this? Say it was taking socks out of draw with the light off.. 1 White to 9 Black. What are chances of having 4 White and 1 Black.. I get 0.00045 ??

More accurately what is the probability that a continuous sequence of 5 presidents out of 43 has 4 left handers?
 
Physics news on Phys.org
There is no particular reason, or improbability against, for a stronly skewed tendency within such a tiny sample.
 
The probability of 4 out of 5 people being left handed is 5C4(.14)(.9)= 5(.0004)(.9)= .00045 as you have. The "out of 43" is irrelevant.
 
I don't think it is irrelevant.

The more presidents there has been the more likley you will get a sequence of 4 out of 5.

If there had been thousands or millions then the chances are that there would be a lot of '4 out of 5's


You would have to look at all the possible conbinations of L and R you could have with 43 presidents and for those that have at least one '4 out 5' work out those combimations' probabilities and add them up. There are maybe short cuts or at least estimates.
 
You could look at this as a problem involving a number of runs in a sequence of Bernoulli trials (president is either left- or right-handed). The sequence is 43 long, and you want the probability of a run of length 4, given p = 1/10.
The question is whether independence would be verified, because of presidents having served multiple terms - but this would apply to the binomial calculation as well.
You could reduce the problem to only the individual presidents and lessen the dependence issue.
At the end of the day, I too would simply write this off as "interesting, but so what".
 

Similar threads

  • · Replies 36 ·
2
Replies
36
Views
5K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
147
Views
11K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
12
Views
5K