Jackathon
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Report Thread starter 11 years ago
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Not sure whether this should be in maths or Biology, but its in my stupid genetics exam on wednesday so I guess its biological.

Basically, I don't get it. Help?
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Abby_B
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umm im guessing your doing applications of genetics on wed?
What bit are you particularly stuck on?

Degrees of freedom is the number of classes minus 1. You use your value of chi squared and locate it in the table corresponding to the degrees of freedom you have. If it helps, in every past paper iv done so far my chi squared value hasn't actually appeared in the table and the probability i have to give is less than 0.001

If the value is less then the critical at 0.05 then the value is significant and you reject the hypothesis that the occurrence is due to chance, its usually due to linkage. Does that help at all?
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Jackathon
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Number of classes minus 1... So how do I use the chi squared result to find the degrees of freedom thing?
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Abby_B
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Say you've tested 4 different types of flowers, the degrees of freedom are just 4-1. This gives you a value of 3. In the papers they usually have a table with degrees of freedom on the left hand column, all you have to do is locate the row that says 3 and read across. If your value of chi squared is in between any of the values in the column you can say that the probability is in between such and such (look at the two values in the table either side of your value. Then look at the column heading at thats the probability) If your value isn't anywhere close to being in the table then look at either end and see which number is closest to the value u have. Depending on which end your value falls between you just say that the probability is less than the lowest value (actually say the number) or greater then the highest value

Does that make any sense?
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