Plan for S2 statistics, November 2017 to January 2018

You may find these two summary sheets useful:

Revision sheet

“Do and don’t” summary of the course

and these notes

How many marks does Edexcel take off for bad writing in S2?

Week 1 (22-23 November)

What S2 is about. Four questions which we’ll be able to answer once we’ve learned the concepts.

Four questions (pdf)

Practical: biased dice.

What is a random variable? It’s really a function rather than a variable. It describes possible outcomes from an activity and attaches probabilities to them so that the probabilities add up to 1.

Binomial distribution: what it is

When to use it

How to calculate by hand

How to use the Classwiz calculator for it


Mean and variance


Answer the first of our “four questions”.

Poisson distribution: what it is

Poisson distribution (ppt)

When to use it

How to calculate by hand

How to use the Classwiz calculator for it


Mean and variance

Ex.2D, 2E, 2F

Answer the second of our “four questions”.

Click here for example of use of Poisson and binomial distributions

Week 2 (29-30 November)

Normal distribution (ppt)

Normal distribution: what it is

When to use it

How to use the Classwiz calculator for it

Relate to binomial and Poisson (also mention Central Limit Theorem, not on syllabus). The rules of thumb for approximations are not stated in the S2 book, and you’re not expected to know them, but they’re usually taken as:

  • Poisson approx for binomial – n big and p small, meaning roughly n ≥ 20 and p ≤ 0.05, and np < 10
  • Normal approx for binomial – n big and p not too small, meaning roughly np > 5 and nq > 5
  • Normal approx to Poisson – λ large, meaning roughly λ > 10

Continuity corrections: if you use a continuous distribution like the normal distribution as an approximation to calculate probabilities for a discrete variable (like binomial or Poisson), then you should calculate normal-distribution probability for the range of continuous values which would round to the discrete values you’re inquiring about. To find P(Discrete Variable=12), take P(11.5 < Normal Variable < 12.5). To find P(Discrete Variable between 12 and 15), take P(11.5 < Normal Variable < 15.5). To find P(Discrete Variable less than 15), take P(−∞ < Normal Variable < 15.5).

Ex.5C, 5D

Answer the third of our "four questions"

Week 3 (13-14 December)

Continuous uniform distribution: what it is

When to use it

How to calculate it

Mean and variance

Recap and intro to CUD (pdf)
Ditto (odt)
and answers to ditto

Continuous Uniform Distribution questions

Which distribution? My own worksheets (below) and Ex.4C Q.5, 6, 9

Which distribution? (pdf)

Which distribution? (ppt)

Week 4 (20-21 December)

Sampling: terminology (which is really all chapter 6 is)

Hypothesis testing: what is a statistic? H0, H1, p, one-tailed, two-tailed, critical value, critical region

Answer the fourth of our “four” questions

Choc chip cookie investigation and debrief (pdf)


Week 5 (10-11 January)

Continuous random variables

Pdf, cdf, mode, quartiles, E(aX+b), Var(aX+b)


Past paper.