You are Here: Home

chi squared psychology watch

1. hi im doing a2 cw and it says on the mark scheme somethig about mentioning critical value. im doing chi squared and my observed value is 75.3 and on the chart it says 0.001. im using df2.
however im not sure wot these facts mean as im crap at maths lol.
cud some1 explain wot they are and tell me wot critical value is
cheers
2. (Original post by emmz)
hi im doing a2 cw and it says on the mark scheme somethig about mentioning critical value. im doing chi squared and my observed value is 75.3 and on the chart it says 0.001. im using df2.
however im not sure wot these facts mean as im crap at maths lol.
cud some1 explain wot they are and tell me wot critical value is
cheers
Okay, I'm not sure how far you've got so I'll start from scratch

(A - B)^2
chi-squared = E -----------
B

Where A= predicted value
B= expected value
E= sum of

Once you have your chi-squared value from this equation (your critical value), you need to compare it to a chart. For this you need n (the number of categories in your data) - as you need to ascertain the degrees of freedom in order to work out what value you need to compare your data with.

Degrees of freedom = n-1

So if you had 4 categories, your degree of freedom would be 3.

You also need to decide on a cut off point - with chi-squared you are assessing whether your data has deviated from the expected data by chance or due to a definite factor in your experiment. Usually a less than 5% probabilty of your data being down to interference is acceptable, thus you need to look for the column where p (probability) = 0.05.

Now find the row where degrees of freedom matches what you have calculated for that, and find the value for that degree that is in the p=0.05 column. This is the value that you need to compare with your chi-squared critical value. If your critical value is LESS than the value in the table, you can conclude that statistically the deviations in your data from the expected values are due to random chance rather than a factor interfering.

I know this is a horribly wordy and scientific information - it's tricky to explain, so if you need more info pm/reply me

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 20, 2004
Today on TSR

Get the low down

University open days

• University of Exeter
Wed, 24 Oct '18
Wed, 24 Oct '18
• Northumbria University