Posted by **Catherine** on Friday, October 28, 2011 at 7:06pm.

I did a biology experiment and I have to use the chi^2 method to calculate statistical significance. I got data at different time points and I just want to make sure what I'm calculating this right. The data I got for one time point are 6 and 23 I know the equation for chi^2 is

chi^2= (obs-exp)^2/exp I calculated my expected value by taking the average of the ones I have, I got 14.5. Will my observed value be any of the two I have, or do I have the add them and that will be my observed value?

- Calculating Chi Squared -
**bobpursley**, Friday, October 28, 2011 at 7:59pm
Actually, I am wondering what you are doing. Chi squared is used to

a) see if a frequency distribution is close to some expected

b) to test the independence of two distributions.

The issue I have is how did you get two data for one time? Are these representative of the same data, or are you comparing two sets to see if independent (statistical significance maybe).

So I need a description of what you are trying to measure, and what you are doing with it.

- Calculating Chi Squared -
**Catherine**, Friday, October 28, 2011 at 8:15pm
I did a biology experiment where I need to analyze the statistical significance of betweeen a data set. My experiment consisted of measuring the effects in photosynthesis and cellular respiration by exposing solutions with leaf discs to different light wavelength. For the statistical significance, I have to compare data I got with blue and green light to white light. The amount of discs for the time point I chose for blue was: 3, white: 23 and for green: 6 I'm supposed to use the chi square method to compare this values and I got 13 for my expected value between blue and white and 8.5 between green and white and then a chi square of 7.69 for blue/white and of 24.735 for green/white. Are those values right? I have to use this method for many other time points but if I have this one right probably I have the others right, same if I have it wrong, if they are wrong, please explain how to calculate it. Thanks

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