Experimental Design

[ktrujillo52]

what do you mean by xi mean?

[eyeball138]

Look at this picture and just follow along with what havenchuck said.
http://www.vensis.ltd.uk/images/standar ... uation.gif

[haven chuck]

Yeah, it just means that you change that every time to one of your inputs. For instance if my inputs were 6, 8, 13, and 19. (mean 11.5) My equation would be like- ... (6-11.5)... (8-11.5)...(13-11.5)...(19-11.5) which is then divied by 3 (since there are 4 inputs minus 1) and then square rooted. I didn't put all the steps in between each set in this example, so make sure you son't forget them.

[ktrujillo52]

Ok I asked my math teacher how to do this last year and she didnt know...


You explained it well, thanks.

[haven chuck]

We did a whole unit on it in math, so it would be hard for anybody in my class NOT to know it.

[eyeball138]

We did a whole unit on it in math, so it would be hard for anybody in my class NOT to know it.

Yeah of course...

Ok I asked my math teacher how to do this last year and she didnt know...You explained it well, thanks.

The fact that your math teacher who is paid to teach math doesn't know standard deviation is a little bit scary.

[binary010101]

For C division, do we have to do Chi square tests?

EDIT: And how does one find standard deviation?
EDIT 2: Can you explain it to a person who hasn't had calc or tried to do math beyond basic trig?

[dickyjones]

I highly doubt it, though it's a nice thing to know in general anyways.

Standard deviation. Take data from 'n' trials. Find the mean value of this set of data...(add all values of data and divide by n). Then for each trial subtract the mean from the actual value measured. Square the result of these. Add the deviations squared of all those trials together. Divide that by how many trials you did minus one (divide by n-1). Take the square root of what you get. see here. The last one was just as good.

Example: Kids in a physics class attempted to measure the acceleration due to gravity and in 3 trials got values of 9.70, 9.73, and 9.80. The mean of this is (9.7+9.73+9.8)/3 = 9.74. So now for each of those measure deviation of trials, square it, and add all together... (9.74-9.7)^2 + (9.74-9.73)^2 + (9.74-9.8)^2 = .0053. Now divide by number of trials minus one... (.0053/2) = .00265. Take the square root...(.00265)^.5 = .0515. Of course you'd pay more attention to showing work and sig figs in your sample calculations.

[ktrujillo52]

wow thanks, you guys seem pretty familiar with this.

Yeah when I asked her she said "Oh thats statistics.....idk"

Last year she was the Honors Algebra II teacher and that is how I had her, she was a horrible teacher though. This year they took her off of honors because everyone complained about her.

[haven chuck]

Oh yeah, dickyjones is right. You divide by n-1, not just n. I fixed my other post. Also, if you need this, the first standard deviation goes is the middle 68% (16 left outside on each side) and the second standard deviation goes out 95% (2.5% left outside on each side). Yoy be asked about this if you use standard deviation so it is good to know.