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# Edexcel S3 - Wednesday 25th May AM 2016 watch

1. (Original post by tazza ma razza)

you apply sxy and sxx etc using the ranks not the actual data
cheers, thats what i thought.
2. Does anybody have the paper asking to test if normal distrubtion is a suitable distrubtion?
3. when doing ch 5 stuff - pmcc and srcc - do you use the ρ in both cases when writing H0 and H1?
4. (Original post by tazza ma razza)

you apply sxy and sxx etc using the ranks not the actual data
I haven't seen a question like this, have you come across one where they've used ranks to calculate PMCC? Textbook and past paper questions only use the data itself to calculate PMCC.
5. (Original post by tazza ma razza)
when doing ch 5 stuff - pmcc and srcc - do you use the ρ in both cases?
Yeh think so.

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6. (Original post by physicsmaths)
Yeh think so.

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as in the hypothesis writing?????
7. (Original post by coolguy123456)
I haven't seen a question like this, have you come across one where they've used ranks to calculate PMCC? Textbook and past paper questions only use the data itself to calculate PMCC.
Yh, but then ranking would be pointless wouldn't it. Ie you would go straight to the pmcc without ranking.
8. (Original post by tazza ma razza)
Yh, but then ranking would be pointless wouldn't it. Ie you would go straight to the pmcc without ranking.
Okay, now I'm confused. Once we have a tie, we average the ranks and calculate the PMCC using only the ranks?
9. (Original post by tazza ma razza)
Yh, but then ranking would be pointless wouldn't it. Ie you would go straight to the pmcc without ranking.
So if they've given data which they've asked to calculate SPCC and then part b for example says 2 ranks are now tied, use PMCC, would we calculate Sxx, Syy, Sxy using the ranks (including the now tied rank)?
10. Really cba to go back to S1 and S2 after this
11. (Original post by Nikhilm)
Really cba to go back to S1 and S2 after this
i got s4 after this
12. (Original post by kennz)
If you are calculating spearmans rank and two units have the same rank, you take an average of that rank and the next and then use PMCC. How would you use PMCC if the data is ranked/ordinal?
What do you mean by "take an average of that rank and the next"?
13. (Original post by coolguy123456)
So if they've given data which they've asked to calculate SPCC and then part b for example says 2 ranks are now tied, use PMCC, would we calculate Sxx, Syy, Sxy using the ranks (including the now tied rank)?
yes

eg sxx = sum of x^2 - (sum of x)^2 /n , where x is the rank, not the data

then multiply the 2 ranks as per for sxy
14. (Original post by tazza ma razza)
Yh, but then ranking would be pointless wouldn't it. Ie you would go straight to the pmcc without ranking.
ranking it and using spearman is quick but less accurate. i thought you do the pmcc u just calculate it from raw data, i might be wrong since im **** at stats.
15. (Original post by Zacken)
Yep, but I doubt the case will arise.
has come up on a past paper i remember, asked you why the degrees of freedom was this value and it was a contingency table, had to combine some frequencies cos one was less than 5
16. (Original post by connorbarr)
has come up on a past paper i remember, asked you why the degrees of freedom was this value and it was a contingency table, had to combine some frequencies cos one was less than 5
Yes, June 15. You had to explain why, but you didn't actually have to combine it yourself which was what I was talking about.
17. (Original post by connorbarr)
has come up on a past paper i remember, asked you why the degrees of freedom was this value and it was a contingency table, had to combine some frequencies cos one was less than 5
june 15 ial
18. (Original post by tazza ma razza)
june 15 ial
no lad i havent done that paper
19. (Original post by connorbarr)
no lad i havent done that paper
June 15 UK.

(Original post by tazza ma razza)
june 15 ial
20. (Original post by connorbarr)
no lad i havent done that paper
my mistake m8

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