1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Chi- squared test-please help

  1. Apr 20, 2010 #1
    Chi- squared test--please help

    Posted this on 12.04.10 but haven't gotten a response. Is my data unclear? Can someone explain how to link the probability to the [tex]\chi[/tex]^2 value please.

    1. The problem statement, all variables and given/known data

    In a cross between two types of pea plants, one heterozygous for the round yellow seed condition, and the other, pure breeding with wrinkled green seeds, the following offsprings were recorded;

    Round yellow peas-- 108
    Round green peas-- 102
    Wrinkled yellow peas--105
    Wrinkled green peas-- 101


    2. Relevant equations

    [tex]\chi[/tex] ^2 = [tex]\Sigma[/tex]{O-E)^2 / E}

    The ratio of a heterozygous cross with a homozygous recessive

    3. The attempt at a solution

    I calculated the value of [tex]\chi[/tex] ^2 to be 0.28. The degrees of freedom= no. of categories-1 = 3.

    I'm a little bit confused on how to relate the calculated value of [tex]\chi[/tex]^2 to the probability value in the distribution table.

    I took the probability value as > 0.1 and got 6.25 according to the data in the table. I'm now assuming that it isn't a significant deviation as the value of [tex]\chi[/tex] ^2 is much smaller than this (0.28).

    Can someone please explain this if I'm on the wrong track. Thanks
     
  2. jcsd
  3. Apr 23, 2010 #2
    Re: Chi- squared test--please help

    http://faculty.southwest.tn.edu/jiwilliams/probab2.gif

    using the above table, first thing you select the row for your degrees of freedom. in your case, it is 3.

    now this row tells us, if your chi square value is less than 0.35, then the probability of this particular event occurring is greater than 0.95. If the chi square value is between 0.35 and 0.58, the probability of this event occurring is between 0.90 and 0.95. And so on.

    your chi square value is 0.28. therefore, the probability of your event occurring is 0.95 or greater.

    now i haven't checked if you have correctly calculated the chi square value. and also, the chi square test is used to test a particular hypothesis. you should have stated your hypothesis.
     
  4. Apr 25, 2010 #3
    Re: Chi- squared test--please help


    Thank you so much! This was very helpful. I realise now i was actually doing the opposite. I was trying to figure out the probability without actually applying the chi square value to the table. HUGE ERROR:redface: I'm trying to learn from a text. Thanks for clearing things up!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook