Sampling Flashcards
What is a population?
The whole set of items
What is a sample?
A subset of the population
What is simple random sampling?
Every sample has an equal chance of being selected
Method of simple random sampling
In sampling frame, each item has an identifying number. Generate a random number to pick a specific piece of data
Advantages of simple sampling
Bias free
Easy and cheap to implement
Each number has an equal chance of being picked
Disadvantages of simple sampling
Not suitable when there is a large population and sampling frame is needed
What is systematic sampling?
Required elements are chosen at regular intervals in ordered list. Take nth element starting at an random item between 1 and n
Advantages of systematic sampling
Simple and quick to use
Suitable for large population
Disadvantages of systematic sampling
Sampling frame is needed
Can introduce bias if sampling frame is not random
What is stratified sampling?
Population divided into strata and simple random sampling is carried out in each group
Advantages of stratified sampling
Reflects population structure
Guarantees proportional representation of groups within population
Disadvantages of stratified sampling
Population must be clearly classified into strata
Selection from each stratum has the same disadvantages as simple random sampling
What is quota sampling?
Population is divided into strata and a quota of an amount of data in each group is set to try refectory the whole population
Advantages of quota sampling?
Allows small sample to be representative of the whole population
No sampling frame required
Quick, easy, inexpensive
Allows for easy comparison between different groups
Disadvantages of quota sampling
Non-random sampling can introduce bias
Population must be divided into groups which can be costly or inaccurate
Non response are not recorded
Increasing scope of study will increase groups which will increase time and cost
What is opportunity sampling?
Sample taken from people who are available at time of study and meet criteria?
Advantages of opportunity sampling
Easy to carry out
Inexpensive
Disadvantages of opportunity sampling
Unlikely to provide a representative sample
Highly dependant on individual researcher
What is cluster sampling?
Population divided into subgroups then taking a sample from just a few of those subgroups
Disadvantage of cluster sampling
Have to make sure the samples don’t affect the accuracy of your sample
