MOD 5 struggling with question

joanne_v

Any ideas? Its worth 3 marks

Reply 1

meerkatt84

5

I've not got the chi square formula in front of me, but you need to use the chi square value given in table 1 to work out whether the change in population from 1976 to 1983 was significant.

I think (think) degrees of freedom here is "1", so for X, chi square corresponds to a probabillity of between 25 and 50%. Again, you'll need to check this, but I'm pretty sure chi square tests the null hypothesis, so this is saying that there is a 50% chance that this is true. Therefore the difference between 1976 and 1983 for X is not significant....

Reply 2

tetedupet

11

isn't it 2 degrees of freedom? (no. categories - 1) = 3-1=2

Reply 3

Demon_AS

13

There are only two categories - 1976 and 1983. So, I would say Degrees of Freedom = 1. My answer would be that there is significant difference because the chi squared value for X is below the critical value (at 0.05 where things become significant) which, according to that annoying table they've given, you is 3.84.

They're reversed it, you see... I'm used to the probability being small on the left and increasing as you read right... so I think they've put that in there to confuse you. As it's below the critical value, you reject the null hypothesis and state that there is a significant difference between what you observe and what you expect (normally it should be accept the null hypothesis if your chi-square value is below the critical value, because the table is usually oriented differently).

So, your answer would be yes, there is a significant difference.

I'm also very tired through lack of sleep, so pencil it in :p:

I could be wrong, but that table is odd... :confused:

Reply 4

Demon_AS

13

meerkatt84

I've not got the chi square formula in front of me, but you need to use the chi square value given in table 1 to work out whether the change in population from 1976 to 1983 was significant.

I think (think) degrees of freedom here is "1", so for X, chi square corresponds to a probabillity of between 25 and 50%. Again, you'll need to check this, but I'm pretty sure chi square tests the null hypothesis, so this is saying that there is a 50% chance that this is true. Therefore the difference between 1976 and 1983 for X is not significant....

It's:

Chi Squared =

(O - E)2
-------- <--- sigma
E

MOD 5 struggling with question

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