My Math Forum  

Go Back   My Math Forum > High School Math Forum > Probability and Statistics

Probability and Statistics Basic Probability and Statistics Math Forum

LinkBack Thread Tools Display Modes
May 28th, 2011, 10:14 AM   #1
Joined: Dec 2009

Posts: 2
Thanks: 0

Probability of gender determination

It is often stated in Biology that the probability of a a baby being a boy is 0.5 (and a girl 0.5).

However there are instances of couples having a sequence of boys (or girls), sometimes 5, 6 or 7 children. For this couple, is P(boy)=0.5 or p>0.5?

If I consider 5 boys out of 6 children, as a hypothesis test (to 5% SL)
P(X=<5) = 0.984, therefore to 5% would reject H0 and accept H1. To 95% confidence there is evidence that P>0.5.

Does this contradict the idea that the P=0.5 for all couples, at every sample?

stuarty77 is offline  
May 28th, 2011, 07:35 PM   #2
Senior Member
Joined: Apr 2011
From: USA

Posts: 782
Thanks: 1

Re: Probability of gender determination

I don't know where the .984 came from - it's a small sample size and I don't know how to do a small sample for a proportion. But there's a couple of comments I could make.

You can get a sample in that rejection range and it doesn't mean the original hypothesis is false. There can be error involved. If you're 95% confidence, there's also 5% chance you're wrong. That 5% exists.

Second, this isn't a random sample - it's a particular set of parents. Another set of parents could have 5 girls out of 6 children. But if the probability of having a boy is indeed .5 (not sure it is), then for each individual child born, it's still .5. (And this is not taking into account whatever biological things could affect this.)

I supposed you could say it contradicts the .5 for "all couples, at every sample," cause it's not like all couples and every sample will turn out that way, and we wouldn't expect it to.
Erimess is offline  
May 28th, 2011, 09:45 PM   #3
Joined: May 2011

Posts: 51
Thanks: 0

Re: Probability of gender determination

Probability is before the event.
It doesn't guarantee the outcome. Let's take a dice and write 6 on it's 5 sides, and on the 1 side left write 1.
In every throw probability of 6 is 5/6 and probability of 1 is 1/6, but still the result can be 1 and that is not contradictory with the probability.
Actually that is called Life

I am a very hard working, dedicated, committed and loyal employee, but my colleague is the hot-new-girl friend of my boss.
Now whatever way I calculate the probability of my promotion, that girl is gonna get promoted, and math. has nothing to do with it.
rudrax is offline  
June 4th, 2011, 04:33 PM   #4
Senior Member
Joined: Apr 2007

Posts: 2,140
Thanks: 0

Originally Posted by stuarty77
It is often stated in Biology that the probability . . .
Since when did the mathematics came along in biology?
johnny is offline  

  My Math Forum > High School Math Forum > Probability and Statistics

determination, gender, probability

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
12-digit number occurrence determination K Sengupta Math Events 1 February 13th, 2010 07:48 AM
Two ratios and prime number determination K Sengupta Number Theory 1 February 4th, 2010 03:14 AM
How find this matrix determination? lolmath123 Linear Algebra 1 December 14th, 2009 01:24 AM
Determination of interval of convergence masiha_devil Real Analysis 1 April 28th, 2009 07:21 PM
Pseudo-Distances within a depth-determination problem Shaitan00 Computer Science 0 November 16th, 2008 01:46 AM

Copyright © 2019 My Math Forum. All rights reserved.