Attempting CT4 Apr 07 Qn 9 & CT4 Sep 07 Qn 4. Why on one question is the number of degrees of freedom reduced, whereas the other makes no allowance. Both questions include the fitting of data to a standard table. Very confusing... Thanks for your help
Hi there, I agree with you, it's difficult to know what to do. The Core Reading is not particularly explicit and yet the Examiner's report criticises students for failing to identify the number of degrees of freedom. Core Reading says: "If we used standard table graduation, we lose one degree of freedom for each parameter fitted, and we lose some further (indeterminate) number of degrees of freedom because of the constraints imposed by the choice of standard table. Rather than suggest how many, it is more important to be aware of the problem when it comes to interpreting the result of the test." So this last sentence surely gives us some degree of freedom (really sad actuarial joke!) in the exam ? The general principle for the test is to lose one degree of freedom for each restriction that is imposed - but without the detail of the number of parameters used in the standard table, this is tricky! The word "indeterminate" says it all really. In the exam, I would be tempted to point out the turning point of the test conclusion. In Apr 2007 Q9, we would need to use just 5 degrees of freedom before we reject H0 - it's fairly safe to conclude here that the gradutaion is good. If it's closer, eg accept with 8, reject with 7 then point this out in your paper - explain the different conclusions? Why not (to really cover yourself) learn the Core Reading sentence "Rather than suggest how many [degrees of freedom], it is more important to be aware of the problem when it comes to interpreting the result of the test." ? Good luck! John
