Achievement Standard – 4 credits, internal

Sir Richie McCaw?  Read read read…

Sir Richie McCaw?  What was the survey question in each article?  How well do the views expressed reflect the views of all NZers?  Why/why not?

Sir Richie McCaw?  How could we gather views of all NZers?  Census? – pros/cons?  …  We take a sample

Homework…  Me as a mathematician…

Sampling methods  How could I select a group of you from a class list in order to check completion of homework?  Discuss different ways that 5 students could be selected

Sampling methods Notes… Basic outline of each method they discussed

Simple random sampling Take a SRS of size 5 to select students to check their homework.

Systematic sampling Take a systematic sample of size 5 to select students to check their homework.

Why take a sample? Purpose of sampling? Reasons for sampling? Features of a good sample?

Why take a sample?  The purpose of taking a sample is  To make an estimate of what is going on back in the population  Reasons for sampling include  Time and cost considerations  Lack of access to the entire population  Nature of the data collection or test (eg blood test, breaking strain of fishing lines…)

Why take a sample?  Features of a good sample  Representative of the population  Sample size is sufficiently large – a small sample is more likely to be unusual and less likely to be representative  NOTE: there is no statistical requirement that a sample be a proportion of the population – a well designed sampling process is more likely to produce a representative sample than a large sample poorly selected  Randomly chosen – each member of the population has the same chance of being included in the sample