1.2 - Random Samples

Explain how to carry out a simple random sam

- create a sampling frame
- use a random number generator and select sampling unit based on this
- this way each item has an equal chance of being selected

State 4 advantages of simple random sampling

1. free of bias
2. easy and cheap for small samples
3. should be representative of the population as each sampling unit has a known and equal chance of selection

State 2 disadvantages of simple random sampling

1. not suitable when the population/sample size is large
2. you need to create sampling frame

Explain how to carry out a systematic random sample

1. divide the whole population by the sample size desired = k
2. record down every kth student from the sampling frame
3. generate the start point randomly between 1 and k=

State 2 advantages of systematic random sampling

1. simple and quick
2. suitable for large samples/populations

State 2 disadvantages of systematic random sampling

1. A sample frame is required
2. If the sample frame is not random it can introduce bias

Explain how to carry out a stratified random sample

1. divide population into mutually exclusive groups called strata
2. divide each group of strata by the total number (Fraction of population)
3. times these strata by the wanted sample number

State 2 advantages of systematic random sampling

1. The sample will accurately reflect the population structure
2. This guarantees proportional representation of groups within a population

State 2 disadvantages of systematic random sampling

1. Population must easily and clearly be classified into distinct strata
2. Within each stratum a sampling frame is needed

Describe systematic sampling

The required elements are chosen at regular intervals from an ordered list

Describe simple random sampling

where every sampling unit has an equal chance of selection

Describe stratified sampling

the population is divided into mutually exclusive strata and a random sample is taken from each