Random sampling

• In random sampling every member of the population has an equal chance of being selected
• Random sampling should be representative of the populatiom
• Random sampling removes bias
• What are the random sampling methods?

  --> simple random

  --> systematic

  --> stratified
• To carry out simple random sampling you need a sampling frame
• There are two methods of choosing numbers in simple random sampling, what are they?


  --> generating random number

  --> lottery sampling: members of the sampling frame are written on tickets and drawn out of a hat
• In systematic sampling the required elements are chosen at regular intervals from an ordered list
• In stratified sampling the population is divided into mutually exclusive strata and a random sample is taken from each
• Number of people in a stratum = number in stratum/number in pop x overall sample size
• What are advantages of simple random sampling?

  --> free of bias

  --> easy and cheap

  --> each sampling unit has a known and equal chance of selection
• What are disadvantages of simple random sampling?

  --> not suitable when the population size of sample size is large

  --> a sampling frame is needed
• What are advantages of systematic sampling?

  --> simple and quick

  --> suitable for large samples and large populations
• What are disadvantages of systematic sampling?

  --> sampling frame is required

  --> Can introduce bias if sampling frame not random
• What are advantages of stratified sampling?

  --> sample accurately reflects the population structure

  --> guarantees proportional representation of groups within a population
• What are disadvantages of stratified sampling?


  --> population must be clearly classified into distinct strata
• What are disadvantages of stratified sampling?


  --> population must be clearly classified into distinct strata