sampling focus questions- - what is sampling? - why should we sample? - what is a reliable sample?
TRANSCRIPT
SamplingFocus Questions- - What is sampling? - Why should we sample? - What is a reliable sample?
Important Statistical Definitions
Population- the set of all things that we are making a statistical inference about.
Inference- Using a sample to make comments about an entire population.
Sample- Some data from the population that we use to represent the population.
In other words...
We take a sample from a population and use the information we get from the sample to make inferences about the population.
We take some data – just enough to represent all of the data – and then use it to make decisions about all of the data.
An example- NZ general election
Before a general election several companies run polls to find out who will win the election.
Their target population is every New Zealander eligible to vote.
The investigations sample some number of eligible voters to decide what the entire population is likely to do.
Focus question 1- What is sampling?
Sampling is....
???
Why should we sample?
The bigger the sample, the better it is. As the sample size increases, it gets closer and closer to the whole population. E.g. My population is 1 million people and I take two samples. The first sample includes 100 people and the second includes 100,000. The larger sample will give me much more accurate data to make inferences.
Why should we sample?
• Time• Money• Ease of Analysis
So why not sample our entire population? (Census)
Focus Question 2- Why should we sample?
We should sample because...
???
What is a reliable sample?
My aim is to figure out who will win the next general election.
I start by walking into an RSA and asking those present (7 people) who they think will win the election.
My results....
National Labour Greens ACT NZ First Other0
1
2
3
4
5
6
7
8
What is a reliable sample?
Next, I decided to go and sample some students in a stage 1 ecology lecture at a university (10 students).
My results...
National Labour Greens NZ First ACT Other0
2
4
6
8
10
12
What is a reliable sample?
What is going wrong with my investigation?
???
What is a reliable sample?
In order to get a good spread of the target population, I decided to randomly sample 100 people that walked by at a local shopping mall.
My results....
National Labour Greens ACT NZ First Other0
5
10
15
20
25
30
35
40
45
What is a reliable sample?
Is this a better sample? Why/why not?
What can be done to improve it?
What may have caused my sample to be less accurate?
What is a reliable sample?
I finally decided to take a sample of 1,000 people walking down the main streets of Whangarei, Auckland, Hamilton, Rotorua, Wellington, Nelson, Christchurch, Dunedin, Queenstown and Invercargill.
My results...
National Labour Greens ACT NZ First Other0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
What is a reliable sample?
How do these results look compared to my others?
What do you think is more reliable?
What could I do to make my sample even better?
Focus Question 3-What is a reliable sample?
A reliable sample is...