1 Flashcards
(30 cards)
What is a population?
A population is the whole set of items that are of interest
What is a census?
A census observes or measures every member of the population.
What is a sample?
A sample is a selection of observations taken from a subset of the population which is used to find out information about the population as a whole.
Advantages of Census
It should give a fully accurate result.
Disadvantages of Census
-Time consuming
-Expensive
-Cannot be used if the testing process destroys the item
Advantages of Sample
-Less time consuming and expensive than Census
-Fewer people have to respond
Disadvantages of Sample
-The data may not be as accurate
-The sample may not be large enough to give info about small sub-groups of the population
What is a Sampling Unit?
Individual units of a population
What is a Sampling Frame?
When sampling units of a population are individually named or numbered to form a list.
Advantages of Simple Random Sampling?
-Free of bias
-Easy and cheap for small populations/samples
-Each sampling unit has equal chances of selection
How do you carry out a simple random sample?
-Get a sampling frame
-Allocate a unique number to each sampling unit
-Use calculator to random number generate
Disadvantages of Simple Random Sampling?
-Not suitable for large population sizes because time consuming and expensive
-Sample Frame is needed
How to do Systematic Sampling?
Choose the required elements at regular intervals from an ordered list
-If sample size 20 required from a population of 100, you would take every 5th person.
How to do Stratified Sampling?
Divide population into mutually exclusive strata (males and females) and take a random sample of each.
What is the formula for the number samples in a stratum?
number in stratum/number in population X overall sample size
Advantages of Systematic Sampling
-Simple and quick to use
-Suitable for large samples and large populations
Disadvantages of Systematic Sampling
-Sampling frame is needed
-It can introduce bias if the sampling frame is not random
Advantages of Stratified Sampling
-Sample accurately reflects the population structure
-Guarantees proportional representation of groups within a population
Disadvantages of Stratified Sampling
-Population must be clearly classified into distinct Strata
-Selection within each strata has the same disadvantages as simple random sampling
What is Quota Sampling?
When an interviewer or researcher selects a sample that reflects the characteristics of the whole population.
How to carry out Quota?
The population is divided into groups according to the characteristics.
What is Opportunity Sampling?
Taking a sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.
Advantages of Quota
-Allows a small sample to be representative of the population
-No sample frame needed
-Quick, easy and cheap
Disadvantages of Quota
-Non random sample can introduce bias
-Population must be divided into groups which may be expensive or inaccurate
