What Is the Probability of Scoring in the 88th Percentile for a Trait as a Male?

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Discussion Overview

The discussion revolves around calculating the probability of scoring in the 88th percentile for a personality trait specifically for males. Participants explore the implications of using continuous and binary probabilities, and how to properly formulate the problem mathematically.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about how to incorporate the 88th percentile into their probability calculations, particularly in relation to gender.
  • Another participant points out that using P(T) for a continuous trait is problematic, suggesting that percentiles do not apply to binary traits.
  • There is a discussion about the proper formulation of the probability, with suggestions to express it as P(IQ>0.88|M) or P(IQ>x|M), where x represents the score corresponding to the 88th percentile.
  • Concerns are raised about the need for a full distribution of scores for males and females to accurately estimate probabilities, indicating that without this, the calculations may involve guesswork.
  • Bayes' theorem is introduced as a potential method to approach the problem, although participants express uncertainty about the initial values and definitions needed for the calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to properly formulate the probability or the implications of using continuous versus binary traits. Multiple competing views on the correct approach remain evident throughout the discussion.

Contextual Notes

Participants highlight limitations in their understanding of the definitions and distributions involved, particularly regarding the application of percentiles to continuous traits and the probabilistic nature of scores.

James Brady
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I scored in the 88th percentile in a certain personality trait and am trying to figure out the probability of that given that I'm male. I'm trying the likelihood that I would land in the 88th percentile given that I'm male.

Definitions: T = trait, M = males, F = female.
Given:
P(T|M) = 0.3
P(T|F) = 0.6

I'm actually having trouble formulating this in mathematical terms even. I'm not sure where the 0.88 comes into play.
 
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P(T) doesn't make sense for a continuous trait, and percentiles don't make sense for a binary trait.
 
So it looks like I'm having to mix binary (male vs female) and continuous (percentile) probabilities and I'm not sure where to starts.
 
The male vs female part is not problematic. It is P(T) that is problematic. Let's say that T is IQ. Then it makes sense to say "I scored in the 88th percentile on IQ", meaning that IQ is a continuous trait and yours is larger than 88% of the population.

But what doesn't make sense is P(IQ). Everybody has an IQ, it isn't a probabilistic thing. What is probabilistic is the score. So you might say P(IQ>100), but you would never say P(IQ)
 
Oh... So I would formulate it as P(IQ>0.88|M)?
 
0.88 is not a realistic IQ value.
You can ask for P(IQ>yourIQ|M) but that's what you want to get, not what you have given.
James Brady said:
Given:
P(T|M) = 0.3
P(T|F) = 0.6
Where does that come from?
 
@mfb That's completely made up. I'm just trying to get a grasp on how to work with the numbers.
 
Ideally you have the full distribution for males and females, or at least some way to estimate that. Otherwise it will be a lot of guesswork.
 
James Brady said:
Oh... So I would formulate it as P(IQ>0.88|M)?
That is close. You can have the probability of one event given another event. That would be like P( In88Percentile | M ). If you know the fraction of males in the 88th percentile, that is the answer.
 
  • #10
James Brady said:
Oh... So I would formulate it as P(IQ>0.88|M)?
Pretty close. If x is IQ for the 88th percentile then you would write it as P(IQ>x|M).

So, for convenience (I am on a mobile device) let's say X is "a person has a score for T which is in the 88th percentile or higher". Then your question is to find P(X|M). The way to do that is with Bayes theorem:

P(X|M) = P(M|X) P(X)/P(M)

Can you work it out from there?
 

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