FM Unit 1 - Data Collection

What is a population?

The whole set of items that are of interest

What is a sample?

Some subset of the population intended to represent the population

What is a sampling unit

Each individual thing in a population that can be sampled

What is a sampling frame

Often sampling units of a population are individually named or numbered to form a list

What is a census

Data collected from the entire population

What is an advantage of a census

Should give completely accurate results

What are disadvantages of a census

Time consuming and expensive

cannot be used when testing involves destruction

large volume of data to process

What are advantages of samples

Cheaper

Quicker

Less data to process

What are disadvantages of samples

Data may not be accurate

Data may not be large enough to represent small subgroups

What is random sampling

By having each sample unit of our sampling flame to have an equal chance of being chosen to avoid bias

What is simple random sampling

Every sampling unit in the sampling frame has an equal chance of being selected

How do you carry out simple random sampling

In a sampling frame each item has identifying number use randoms number generator or lottery sampling

What are advantages of simple random sampling?

• Bias free

• Easy and cheap to implement

• Each number has a known equal chance of being selected

What are disadvantages of simple random sampling?

• Not suitable when population size is large

• Sampling frame needed

What is systematic sampling?

Required elements are chosen at regular intervals in ordered list

How to carry out system sampling?

Take every kth elements where k = population size/sampling size starting at random item between 1 and k

What are advantages of systematic sampling?

• Simple and quick to use

• Suitable for large sample/populations

What are advantages of systematic sampling

• Sampling frame again needed

• Suitable for large samples/populations

What are disadvantages of systematic sampling

• Sampling frame again needed

• Can introduce bias if sampling frame not random

What is stratified sampling

Population divided into groups called strata and a simple random sample carried out in each group used when sample is large and population naturally divides into groups

How to carry out stratified sampling

Sample size divided by population size sampled from each strata

What are advantages of stratified sampling

Guarantees proportional representation of groups within population

Reflects population structure

What are disadvantages of