Year 12s: what will be the first way you research your future options? >>

Chi-squared tests

For 7b one of the expected frequencies is less than 5 so why haven’t they pooled the Variables before they worked out X^2?
https://imgur.com/a/zvKU3f5

Reply 1

AzureCeleste

It's if more than 20% of the expected results are less than 5 then you pool together.
You only always pool results together when the expected frequency is less than 1

Reply 2

Y2_UniMaths

Original post by AzureCeleste

It's if more than 20% of the expected results are less than 5 then you pool together.
You only always pool results together when the expected frequency is less than 1

I’m not sure where you’ve got these figures from? The textbook doesn’t mention anything like that and the CGP guide says “all expected values must be at least 5”

Reply 3

AzureCeleste

Original post by Y12_FurtherMaths

I’m not sure where you’ve got these figures from? The textbook doesn’t mention anything like that and the CGP guide says “all expected values must be at least 5”

That's how I was always taught it. I was on a different exam board but we were taught only to combine groups together if more than 20% of the expected frequences were less than 5 or if they were less than 1

Reply 4

Y2_UniMaths

Original post by AzureCeleste

Are you able to explain the difference between these two formulas? Because I don’t really understand what the second one means https://imgur.com/a/b2n1kgR

Reply 5

AzureCeleste

Original post by Y12_FurtherMaths

Are you able to explain the difference between these two formulas? Because I don’t really understand what the second one means https://imgur.com/a/b2n1kgR

They're the same?
One's just saying that it is approxiametly the same as X^2v

Reply 6

Y2_UniMaths

Original post by AzureCeleste

They're the same?
One's just saying that it is approxiametly the same as X^2v

Right I see thanks. Tagging @RDKGames as I’m still unsure on the pooling issue

Reply 7

AzureCeleste

Original post by Y12_FurtherMaths

Right I see thanks. Tagging @RDKGames as I’m still unsure on the pooling issue

https://en.wikipedia.org/wiki/Pearson%27s_chi-squared_test

It's explained here if you go down to expected cell count under assumptions

Reply 8

Y2_UniMaths

Original post by AzureCeleste

https://en.wikipedia.org/wiki/Pearson%27s_chi-squared_test

It's explained here if you go down to expected cell count under assumptions

It sort of makes sense, but idk if that’s just for Edexcel? I think that’s the exam board since I’m on AQA and all it says for me is just “greater than 5”

Reply 9

AzureCeleste

Original post by Y12_FurtherMaths

It sort of makes sense, but idk if that’s just for Edexcel? I think that’s the exam board since I’m on AQA and all it says for me is just “greater than 5”

It will vary from exam board to exam board.
Are the questions you doing specific to your exam board or not?

Reply 10

Y2_UniMaths

Original post by AzureCeleste

It will vary from exam board to exam board.
Are the questions you doing specific to your exam board or not?

It doesn’t specifically specify they are AQA based questions but one would assume so since they’re taken from a mixed practice section in the AQA textbook