Data Collection Flashcards
Define population
The whole set of items that are of interest
What is a census?
It observes or measures every member of a population
Define sample
A selection of observations taken from a subset of the population which is used to find out information about the population as a whole
What are the advantages of a census? (1)
It should give a completely accurate result
What are the disadvantages of a census? (3)
Time consuming & expensive
Cannot be used when the testing process destroys the item
Hard to process large quantity of data
What are the advantages of a sample? (3)
Less time consuming and expensive than a census
Fewer people have to respond
Less data to process than in a census
What are the disadvantages of a sample? (2)
The data may not be as accurate
The sample may not be large enough to give information about small sub-groups of the population
What is a sampling unit?
Individual units of a population
What is a sampling frame?
A list of named/numbered sampling units of a population
Describe what is meant by random sampling
Every member of the population has equal chance of being selected
∴ the sample should be REPRESENTATIVE
And also helps remove BIAS
What are the three methods of random sampling?
Simple random sampling
Systematic sampling
Stratified sampling
What 3 things do you need for a simple random sample?
A sampling frame
Where each person or thing is allocated a unique number
And a selection of these numbers is chosen at random
What 3 things do you need for a simple random sample?
A sampling frame
Where each person or thing is allocated a unique number
And a selection of these numbers is chosen at random
What are the 2 methods of choosing a selection of random numbers?
Generating random numbers
Lotterty sampling
Describe systematic sampling
The required elements are chosen at regular intervals
From an ordered list
(eg. Population = 100, Sample size = 20, you would take every 5th person since 100/20=5)
The first person to be chosen should be chosen at random
(So the next would be 7, 12, 17 etc.)
Describe stratified sampling
The population is divided into mutually exclusive strata (eg. males and females)
And a random sample is taken from each
The proportion of each strata sampled should be the same
The number sampler in a stratum=(number in stratum/number in population)×overall sample size
What are the advantages of simple random sampling?
Free of bias
Easy and cheap to implement for small populations and small samples
Each sampling unit has a known and equal chance of selection
What are the disadvantages of simple random sampling?
Not suitable when the population size or the sample size is large
A large sampling frame is needed
What are the advantages of systematic sampling?
Simple and quick to use
Suitable for large samples and large populations
What are the disadvantages of systematic sampling?
A sampling frame is needed
It can introduce bias if the sampling frame is not random
What are the advantages of stratified sampling?
Sample accurately reflects the population structure
Guarantees proportional representation of groups within a population
What are the disadvantages of stratified sampling?
Population must be clearly classified into distinct strata
Selection within each stratum suffers from the same disadvantages as simple random sampling
What are the two types of non-random sampling?
Quota sampling
Opportunity sampling
Define quota sampling
An interviewer or researcher selects a sample that reflects the characteristics of the whole population
