• We are pleased to announce that the winner of our Feedback Prize Draw for the Winter 2024-25 session and winning £150 of gift vouchers is Zhao Liang Tay. Congratulations to Zhao Liang. If you fancy winning £150 worth of gift vouchers (from a major UK store) for the Summer 2025 exam sitting for just a few minutes of your time throughout the session, please see our website at https://www.acted.co.uk/further-info.html?pat=feedback#feedback-prize for more information on how you can make sure your name is included in the draw at the end of the session.
  • Please be advised that the SP1, SP5 and SP7 X1 deadline is the 14th July and not the 17th June as first stated. Please accept out apologies for any confusion caused.

Q&A Bank Part 4 qstn 4.3 (Continuity Correction)

J

johnmunge

Member
When calculating the value of our test statistic I noticed that 0.5 has been deducted from the value of X(=18). In other examples(cant remember which specifically) we ADDED 0.5 to the value rather than deducting.

Therefore my question is, when carrying out a hypotheses test what determines whether we add or subtract 1/2 after contuity correction. I am guessing that it has to do with the direction of the alternative hypothesis, and if this is the case how will we carry out continuity correction if the alternative hypothesis is a simple one e.g
H0: p = 0.9
H1: p != 0.9 (!= is "not equal")

thanks :)
 
johnmunge said:
When calculating the value of our test statistic I noticed that 0.5 has been deducted from the value of X(=18). In other examples(cant remember which specifically) we ADDED 0.5 to the value rather than deducting.

Therefore my question is, when carrying out a hypotheses test what determines whether we add or subtract 1/2 after contuity correction. I am guessing that it has to do with the direction of the alternative hypothesis, and if this is the case how will we carry out continuity correction if the alternative hypothesis is a simple one e.g
H0: p = 0.9
H1: p != 0.9 (!= is "not equal")

thanks :)
Click to expand...

The shortcut rule is that you adjust it by 0.5 towards the mean of the distribution.
 
John Lee said:
The shortcut rule is that you adjust it by 0.5 towards the mean of the distribution.
Click to expand...
Hi John,
Thanks for the comments and this is what the study material also mentions.
Could you please elaborate on the reason and logic behind adding/subtracting 0.5 towards mean as I am unable to locate it in the study pack.
Many thanks.
Sunil
 
So this "towards the mean" is only used in hypothesis tests in Chapter 10.

This is because when we calculate the p-value for the binomial/Poisson we include the observed value. So if H0:p=0.8 vs H1:p>0.8 and we observe X=42 successes out of 50 trials for X~Bin(50,0.8), then the p-value will be P(X>=42) which continuity corrects to P(X>=41.5) which is closer to the mean of np=50*0.8=40.

Similarly, if we were testing H0:p=0.8 vs H1:p<0.8 and we observe X=36 successes out of 50 trials for X~Bin(50,0.8), then the p-value will be P(X<=36) which continuity corrects to P(X<=36.5) which is closer to the mean of np=50*0.8=40.
 
You must log in or register to reply here.
Back
Top