Textbook errors - Y2 Stats:
https://docs.google.com/document/d/1RtvYyMvLvfX7pWzHYhX-BZqOpZLtjyYr/edit#bookmark=id.3znysh7
updated July 2022 for third printing
Chapter 1
The book does not make clear that the ax^n formula is a “Power” model, while the kb^x is an “Exponential” model, which corresponds to the terminology used on Excel. The chapter uses exponential for both, which is incorrect. It’s only exponential if the independent variable is the power.
Exercise 1A, questions 4 and 8, page 3
These two questions ask for an interpretation of b in the exponential model y = a bx
Question 4 says “when x increases by 1 (month), y increases by 20% (population)”
Question 8 says “b is the rate of change of y per increase of x by 1”
This second sentence is incorrect, the rate of change is dy/dx which is not b.
Stick with the first phrasing until we have markscheme guidance on this.
Exercise 1B, questions 4 and 5, page 7
These have now been corrected online, but may be wrong or missing in some printings of the book.
Question 4 should have the regression line as y = 2.487 - 0.320x
[Pedantic point - using Excel you can see that we should be using “Power” model rather than “Exponential” model for a good fit, but it’s too much bother to change that as well - they have just made up dodgy data that is not exponential decay!]
Question 5 should have the regression line as y = 0.464 + 1.88x
This one does use the Power model and is a good fit.
Exercise 1C, question 4b, page 11
The question in the book originally said “evidence of a linear relationship” which means using a two-tailed test. It now says “evidence of a positive linear relationship”
The answer in the back uses a one-tailed test with critical value 0.6215 at 5%, instead of 0.7067 at 2.5%. This changes the conclusion from significant to not significant.
Make sure students are doing one tailed.
Mixed Exercise 1, question 2a, page 12
Textbook question and answer correct, using log d = -0.635 + 0.0334x. The worked solutions are wrong as they use a different equation. The book equation has been checked on Excel.
Mixed Exercise 1, question 6b, page 13
The question in the book says “suggested there is no correlation” which means using a two-tailed test. The answer in the back does this, comparing r = 0.340 with critical value 0.6319 at 2.5%.
The worked solutions make a gigantic hash of it, first saying “2 tailed” when using rho > 0, and then using a Spearman’s rank value (not on the spec) instead of the value from a. Definitely ignore.
Exercise 2A, question 4f, page 19
The question is asking for a probability, so should read P(K’ n C)
Still not corrected in second printing.
Exercise 2D, question 11c, page 30
The book answer of P(A n B) should be 0.1. This has been fixed in the second printing and online.
Section 2.5, Example 8, page 31
The question mentions both beads and balls. It should be beads throughout.
Exercise 2E, question 3a, page 32
The tree diagram in the answers has incorrect fractions on the second column of branches (mainly because they simplified 10/24 to 5/12 then subtracted 1 from each). They should be 9/23, 14/23, 10/23, 13/23. This has been fixed in the second printing and online. A reminder to students NOT to simplify fractions in conditional probability trees!
Exercise 3A, question 7, page 41
The original answers in the printed book are wrong, now corrected. Mean is 56.5 and sd is 4.5, so needs the answer 4.5^2 for variance.
Exercise 3B, questions 3 and 4, page 43
The answers in the second printing have put a weird part i and part ii which do not match the question. The answers should be 3a) 0.1587, 4a) 0.2635
They are unchanged online
Also, the variable in question 3 should be Y. This has been fixed online, but not in the second printing!
Exercise 3E, questions 12 and 13, page 52
While the answers are not wrong, it is possible for the students to get different ones. 65% in question 12 means they can use 0.35 in the normal look-up table so their answer is only correct to 4dp, affecting their final answer. If they use 65% on their calculator for inverse Z normal, they get a more accurate answer which leads to the book’s final answer. Same with question 13.
Exercise 3F, question 2c, page 55
First printings of the book have the wrong answer. It should be 0.6723. The online books and worked solutions are correct.
Exercise 3F, question 3b, page 55
The first printing of the book has the wrong answer. It should be 0.511 or 0.5115. The worked solutions are correct. This has been fixed online.
Exercise 3F, question 9, page 55
The original book has the wrong answer. It should be 0.31%. This has been fixed in the second printing and online.
Exercise 3G, question 2c, page 58
The book is correct. The worked solutions do mu > 85 by mistake.
Exercise 3G, question 6c, page 59
The question has been amended online and in the worked solutions. It now has n = 10 and observed value 5.65 mm. The latest printed book still has 20 and 5.52.