1. CONFIDENCE INTERVALS USING YOUR GDC Stats 1 with Liz

2. JANUARY 2012, Q7 Questions like this show the importance of knowing your formulae instead of simply relying on your GDC to do all the work for you!

3. JANUARY 2012, Q7 If this were a normal distribution, then the curve would look like: The distribution cannot be “normal” because it is impossible for someone to earn a negative salary. To get full marks, you must have the description on the left. However, instead of drawing the entire curve, you could simply show:

4. JANUARY 2012, Q7 You can assume that it is normally distributed because the sample size is large (n = 50), and by the central limit theorem, any sample size above 30 (n > 30) can be assumed to be normal.

5. JANUARY 2012, Q7 To construct a 99% C.I. we can use the following formula, where z = 2.576: Since we don’t know the population s.d. ( ), we’ll use the sample s.d. ( ) instead. To get a z value in your calculator: MENU STAT DIST (F5) NORM (F1) InvN (F3) Data: Variable Tail: Central (always this with C.I. questions) Area: 0.99 (the percentage or probability you’re given) : 1 (standard normal s.d.) : 0 (standard normal mean) Save Res: None (don’t change this!) EXE

6. WORKING OUT CONFIDENCE INTERVALS SOLELY IN THE GDC… Before we continue… please be warned! This method is not recommended because if you don’t show any work and you do not get the correct solution, you will gain no method marks. I only use this method to check my solutions! To work out any confidence interval in your calculator: MENU STAT DIST (F5) NORM (F1) InvN (F3) Data: Variable Tail: Central (always this with C.I. questions) Area: 0.99 (the percentage or probability you’re given) : (the standard error ) : 45.8 (sample mean ) Save Res: None (don’t change this!) EXE

7. JANUARY 2012, Q7 It is unlikely that the annual salaries have an average which exceeds £55 000 because it is above the confidence interval, so this claim can be rejected. The original question stated: which is only 6/50 = 12%, so it can be rejected that more than 25% of such salaries exceeds £60 000. Note: when a confidence interval for an unknown population mean,, does not include the value claimed for, there are grounds for rejecting the claim.

8. EXPECT A MINI QUIZ OVER ESTIMATION ON TUESDAY. S1 MOCK EXAM HELD ON WEDNESDAY, 29 TH APRIL FROM 2:05PM – 4:10PM IN ROOM C1.5 PLEASE SEE ME IF YOU CANNOT MAKE THIS TIME. FULLY READ YOUR GDC BOOKLET & GO THROUGH ALL EXAMPLES. THIS WILL HELP YOU FOR YOUR EXAM!

9. DO NOT LEAVE WITHOUT HANDING IN YOUR TEST OVER NORMAL & BINOMIAL DISTRIBUTIONS