Chapter 1 - Data Collection Flashcards
Methods of Random Sampling
Simple Random, Systematic & Stratified
Simple Random Sample
Everyone has an equal chance of being chosen
Advantages of a Simple Random Sample
Free of bias, Easy and cheap to implement for small populations and small samples. Each sampling unit has a known equal chance.
Disadvantages of a Simple Random Sample
Not suitable when the population size or the sample size is large as it is time consuming, disruptive and expensive, sampling frame needed
How to carry out a Simple Random Sample
Using your sampling frame, number all the elements and use random number generator to generate x different numbers.
Systematic Sampling
Required elements chosen at regular intervals
Advantages of Systematic Sampling
Simple and quick to use, suitable for large samples and large populations, every member has the same probability of being chosen.
Disadvantages of Systematic Sampling
Sampling frame needed, can introduce bias if sampling frame is not random.
How to carry out a systematic sample
Take every Kth element where K= Population Size / Sample Size. Choose starting point between 1 and K using a simple random sample.
Stratified Sampling
Population divided into mutually exclusive strata
Advantages of Stratified Sampling
Accurately reflects population structure, Guarantees proportional representation of groups within population.
Disadvantages of Stratified Sampling
Population must be clearly classified into distinct strata, Selection within each stratum suffers from same disadvantages as simple random sampling
How to carry out a stratified sample
Population divided into groups (strata) and a simple random sample carried out in each group. Same proportion, sample size / population size, used when sample is large and population naturally divides into groups.
Methods of Non-random Sampling
Quota & Opportunity
Quota Sampling
An interviewer or researcher selects a sample that reflects the characteristics of the whole population
Advantages of Quota Sampling
Allows small sample size to still be representative of the population, no sampling frame required, quick, easy, inexpensive, allows for easy comparison between different groups within a population.
Disadvantages of Quota Sampling
Non-random sampling can introduce bias, population must be divided into groups which can be costly and inaccurate, increasing scope of study increases number of groups which adds time and expense, non-response are not recorded,
How to carry out a Quota Sample
Population divided into groups according to characteristic. A quota of items / people in each group is set to try and reflect the group’s proportion in the whole population. Interviewers selects the actual sampling units.
Opportunity Sampling
Taking a sample from people who are available at the time of study is carried out and who fit the criteria you are looking for.
Advantages of Opportunity Sampling
Easy to carry out, inexpensive.
Disadvantages of Opportunity Sampling
Unlikely to provide a representative sample, highly dependent on individual researcher.
Quantitative Data
Variables or data associated with numerical observations
Qualitative Data
Variables or data associated with non-numerical observations
Continuous Data
Can take any value in a given range
Discrete Data
Can only take specific values
Sampling Unit
Individuals units/items of a population
Census
Observes or measures every member of a population
Advantages of a Census
Should give completely accurate result
Disadvantages of a Census
Time consuming and expensive, cannot be used when the testing process destroys the item, hard to process large quantity of data
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.
Advantages of a Sample
Less time consuming and expensive than a census, fewer people have to respond, less data to process than in a census.
Disadvantages of a Sample
The data may not be as accurate, the sample may not be large enough to give information about small sub-groups of the population.
