This week in AP Biology we went over chi2 (sounds
like ky). Chi2 is used to test a null hypothesis, in other words it
can be used to see if there is a significant difference in what is observed and
what is expected. The formula for chi squared is:
The X2c represents chi2
The ∑ is a symbol for a summation.
Oi is the observed data, the data you have
collected
Ei is the
expected data, what you would get in a perfect world.
To determine if the discrepancies between the numbers are to
large you look at the critical value and degrees of freedom chart.
The chart gives you the number that your answer from the chi2
formula must be under for you to accept the null hypothesis.
Chi2 is commonly used in genetics to determine
phenotypes.
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