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    two way tables




    Maybe there is no way to do this on this format. However, I am a bit stuck on a question about showing proportions on a two way table....probably just need to sleep on it and come back to it but will ask anyway.
    I understand that the table is a means of showing proportions that equal 1.0. The question gives this data:
    .01% of pop. is schizophrenic
    .8% of pop. is homeless
    1/3 of the homeless have schizophrenia.
    On a two-way table show proportion of people with schizophrenia who are homeless.
    Okay. I look at this and want to say that if I multiplied .333 by .8 I would get the answer as to how many homeless people have schizophrenia. But to put it on the table?... I tried the algebraic table with B and Not B on top and A and not A on left side and then used pr(A and B), pr(A and not B) etc with all supposed to be totalling 1.0 in the bottom right hand square. Wasn't sure what to put on the top and the side...I think this uses the multiplication rule.
    Am I heading in the right direction?
    E

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    Are you sure the following statement is worded correctly:

    "1/3 of the homeless have schizophrenia"

    The reason I ask is that if we are given that .01% of the population has schizophrenia, and .8% are homeless, then 1/3 of the homeless equates to 0.27% of the population, which is larger than .01%

    The 2-way table works out if you re-word it to say:

    "1/3 of people with schizophrenia are homeless"

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    2-way help

    Yes the wording is "1/3 of the homeless are schizophrenic".
    I think the other statement: "1% pop. is schizophrenic" refers to our total population, not the population of people who are schizophrenic or who are homeless.
    Does that change anything? I get the feeling that the 1% won't make a difference to the 2-way table. I'll give it a try.
    Thanks again!
    E

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    Is it 1% or .01% ?

    Yes, I understand that it refers to the total population (i.e., one of the "marginal" values).

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    2-way

    Hi Again
    It actually says"1%" not .01%...is there a difference?
    Thanks
    E

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    and..

    The question quotes exactly these numbers:
    1% of pop. is schizophrenic
    0.8% of the pop. are homeless (can this be correct?)
    and "one third of the homeless are schizophrenic".
    Says they're quoting a Time magazine story from 1992
    Do you think there is a type-o? Now that I look at the numbers they seem a bit out of wack....what does .8% mean? Wouldn't .8 = 80%?
    Dazed and confused.
    I guess the main point is to find the proportion which I will try to figure out first and then plot on 2-way table.
    Thanks
    E

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    Quote Originally Posted by greenatstats
    Hi Again
    It actually says"1%" not .01%...is there a difference?
    Thanks
    E
    Yes. 1% means .01 or 1/100 and .01% means .0001 or 1/10000
    0.8% would mean .008 or 8/1000

    Now you can construct a 2-way table. Put schiz/no schiz across the top, and homeless/not homeless along the left.

    Let's say that, for starters, the size of the population is 100,000. Now, we're given that 1% have schiz. and .8% are homeless. So, 1% of 100000 is 1000, and .8% of 100000 is 800. We are also told that 1/3 of the homeless have schiz. so 800*(1/3) = 267.

    Put the total population outside the table in the lower right-hand corner, and fill in the values given above, and it should be an arithmetic exercise to fill in the blanks.

    "On a two-way table show proportion of people with schizophrenia who are homeless."
    - to answer this question, just divide the number in the schizo+homeless box by the total number of people with schiz.

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    Smile 2-way help


    Thank you so much....of course when you put it on the screen I do see the difference in the %'s and realize, of course!, I know that...but sometimes just can't see it for looking to hard.
    E

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