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Standard Gamma Distribution

  1. Mar 31, 2010 #1
    1. The problem statement, all variables and given/known data
    This is an example in my book with omitted steps. Suppose the reaction time X of a randomnly selected individual to a certain stimulus has a standard gamma distribution with alpha=2. When X is continuous

    P(2<=X<=5) = F(5;2)-F(3;2) = .960-.801 = .159

    2. Relevant equations

    F(x;alpha) = integral from x to 0 [(y^(alpha-1))*(e^-y)]/(gamma(alpha)

    3. The attempt at a solution

    I have followed the equation and placed 5 for y and 2 for alpha but the numbers are not matching up. In the test it says that gamma(alpha) is equal to one. Please help I have a test tommorow. Thanks
  2. jcsd
  3. Apr 1, 2010 #2
    What exactly is the problem? What numbers are you expecting and what numbers are you getting?

    You write:
    P(2 <= X <= 5) = .159
    but is this what you're supposed to get, or what you're actually getting?

    I get P(2 <= X <=5)=.159 as well using the exact formulas you posted (minor nitpick: the integral is from 0 to x, not from x to 0, but I assume this was just a typo).
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