This discussion is now closed.

Check out other Related discussions

chi squared test

CHI SQUARED TEST

....anyone - how?? why?? whats it for??

apparently i have to know how to do this for my AQA A biology exam. sooo..help?! :eek:

thankees xxx

Reply 1

wackysparkle

14

the chi squared test is used with 2 or more sites of data.
Its is used when u want to compare ur data to a particular biological theory, e.g. medel.
U obtain a chi value and if it is greater than the critical value it implies that there is a significant difference between the observed and expected data, and the null hypothesis is rejected and ur original hypothesis stands.
In edxexcel they normally tell u what the test is about, and just give u the info, i don't know about aqa, but don't they do that as well?

also, this test is normally not mentioned in past papers,

Reply 2

mawi99102

chi squard test is used to test for goodness fo fit, which essentially means that you have an expected value say the mendellien ratio 3:1 , then you test your results against that at the p<0.05 confidence level.

if the value is higher than the critical value at p<0.05 then you reject the null hypothesis.

for edexcel we don't need to work out the statistics but we do have to know how to read off the critical value off the table provided

Reply 3

angelsintuition

I'M DOING OCR (BOOO) & JUST SAW A PAST PAPERS WHERE THEY EXPECT YOU TO DO THE WHOLE CHI-SQUARED. TOLD U FORMULA BIT NOT HOW TO USE THE COMPARISON GRAPH. JUST TO CLARIFY THIS IN MY HEAD IF SAY U GET UR RESULTS MORE THAN 5% THAT MEANS THAT U ACCEPT OR REJECT UR HYPOTHESIS? WHAT (IN PLAIN SIMPLE TERMS PLEASE FOR THIS BAFFLED GAL) IS IT ACTUALLY MEASURING ???

Reply 4

angelsintuition

OH AND WAT THE BUGGER IS A T TEST ??

Reply 5

Nitzy

1

If the result is below the critical value (5%) you accept your null hypothesis which means that theres no significant difference between the results and vise versa. The whole point of it is to see if there is any significant difference between the observed results and the expected results. (I believe it pointless but hey).
T - test simlar to chi squared but I don't think that would come up in an OCR exam we did it for coursework very long and boring.
Hope that makes some sense.

Reply 6

Mushu

does the edexcel board need to know this?

Reply 7

Revenged

15

angelsintuition

I'M DOING OCR (BOOO) & JUST SAW A PAST PAPERS WHERE THEY EXPECT YOU TO DO THE WHOLE CHI-SQUARED. TOLD U FORMULA BIT NOT HOW TO USE THE COMPARISON GRAPH. JUST TO CLARIFY THIS IN MY HEAD IF SAY U GET UR RESULTS MORE THAN 5% THAT MEANS THAT U ACCEPT OR REJECT UR HYPOTHESIS? WHAT (IN PLAIN SIMPLE TERMS PLEASE FOR THIS BAFFLED GAL) IS IT ACTUALLY MEASURING ???

Well the other posters - there have been two of you now! - have been wrong about the p-value... tut tut! :wink:

P-value means the probability that the results are due to chance...

If you get a p-value of 0.05 then this means there is a 5% chance that the results are due to chance...

If you do the test and find that you get a value of 0.01 then this means that there is a 1% chance that the results are due to change, thus the p<0.05 (which means that the probability the results are due to chance is less than 5%) and so YOU REJECT THE NULL HYPOTHESIS (at the 95% confidence interval)!

I'm very worried why any of you think that you use any of this data from the chi or t-test to accept the null hypothesis... you can never accept the null hypothesis using this test!... if you get a p-value of 0.06 this means that there is a 6% chance that the results are due to chance - this does NOT state that there must be no relationship between the results you have obtained (which is what you mean when you are accepting the null hypothesis)...

If p>0.05 you can also say that "there is not enough evidence to disprove the null hypothesis"

Reply 8

wackysparkle

14

well i do statistics, and that is actually what u say whenever u do a statistical test.
Also, if u read up on the tools and techniques book, u will see that this is also what they say,,,,,as well as marking schemes.

Reply 9

Revenged

15

wackysparkle

well i do statistics, and that is actually what u say whenever u do a statistical test.
Also, if u read up on the tools and techniques book, u will see that this is also what they say,,,,,as well as marking schemes.

Nah, I never meant that you said anything wrong...

I was referring to these statements...

"if the value is higher than the critical value at p<0.05 then you reject the null hypothesis."

"If the result is below the critical value (5%) you accept your null hypothesis which means that theres no significant difference between the results and vise versa."

Reply 10

wackysparkle

14

okay.......... :smile:

Reply 11

-doll

OP

sooo.... (sorry to be so thick here) ...

"if the value is higher than the critical value at p<0.05 then you reject the null hypothesis."

"If the result is below the critical value (5%) you accept your null hypothesis which means that theres no significant difference between the results and vise versa."

those ^^ statements are wrong?? ahhhh. :s

Reply 12

wackysparkle

14

yip, sounds rite! :smile:

chi squared test

Related discussions

Latest

Trending

Trending

Articles for you