Chapter One: Statistics Flashcards
Who will a census ask?
Everyone
Who will a sample ask?
A representative subset
Benefits of a census
Completely accurate in result (unless lying / leading question e.g., “Isn’t the film great?”
Downsides of a census
- Time consuming / expensive
- Can’t be used when testing process destroys item (e.g., if apples are ripe you’d have to destroy)
- Hard to process large quantities
Positives of taking a sample
- Less time consuming / expensive
- Less data
- Less people
Negatives of taking a sample
- Not as accurate
- Subset may not represent a population if sample is too small.
How could an experiment be improved?
Ask more people.
Individual units of a population are known as what?
Sampling units.
What is the list of all items called?
Sampling frame (not always possible e.g., everyone in Birmingham)
What are the 3 random sampling methods?
Simple random sampling
Systematic Sampling
Stratified Sampling
What do all random sampling methods require?
A sampling frame
Why do all random sampling methods require a sampling frame?
To have a list to pick sampling units from.
How to conduct a Simple Random Method
Random Number Generator or pick from a hat
Advantages of simple random method
No bias
Easy and Cheap
Each sample has a known and equal chance of being chosen.
Disadvantages of simple random method
Not suitable with a large population / sample size
Sampling frame needed
How to conduct systematic sample
People chosen at a random interval from ordered list.
Benefits of systematic sampling
Simple and quick
Suitable for large samples and populations.
Disadvantages of systematic sampling
Sampling frame needed
Can introduce bias if not random (may miss out smaller populations)
How does stratified sampling work?
Divide population into groups and pick using simple random sampling (select withing stratum).
In stratified sampling, how do you calculate how many you should test within a subset?
(total from group / total overall) x number you want to sample in experiment
Advantages of stratified sampling
Sample accurately reflects population structure
Guarentees proportional representative of groups in a population.
Disadvantages of stratified sampling
Sampling frame needed
Population must be clearly classified into distinct strata.
Selection in strata suffers same disadvantages as simple random sampling.
