Chapter 1: Data Collection Flashcards
What is a census?
A census is when you ask all pupils
What is a sample?
A sample is when you ask a representative subset of the pupils.
Advantages of a census
-leads to completely accurate results
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
Advantages of a sample
less time consuming and more expensive than a census
fewer people have to respond
less data to process than in a census
Disadvantages of a sample
data may not be as accurate
sample may not be large enough to give information about small sub-groups of the population
Improvement: Use a large sample size
what are sampling units?
Sampling units are individual units of a population
what is a sampling frame?
A sampling frame is where sampling units of a population are individually named or numbered to form a list
Random sampling
In random sampling, every member of the population has an equal chance of being selected so the sample is therefore representative of the population. Random sampling also helps to remove bias from a sample.
Simple Random sampling
Simple random sampling is where every sample of size n has an equal chance of being selected e.g draw names from a hat or assign each pupil of a number and use a random number generator
Advantages of a simple random sample
-free of bias
-easy and cheap for small populations
-each sampling unit has a known and equal chance of selection
Disadvantages of a simple random sample
-not suitable when the population size is large
-a sampling frame is needed
Systematic sampling
Systematic sampling is where the required elements are chosen at regular intervals from an ordered list
Advantages of a systematic sampling
-simple and quick to use
-suitable for large samples and large populations
Disadvantages of systematic sampling
-a sampling frame is needed
-can introduce bias if sampling frame is not random
Stratified sample
A stratified sample is when a population is divided into mutually exclusive strata such as males and females, juniors and seniors and a random sample is taken from each
Advantages of a stratified sample
-accurately reflects the population structure
-guarantees proportional representation of groups within a population
Disadvantages of a stratified sample
-population must be clearly classified into distinct strata
-sampling frame is needed
Non-random sampling methods: Opportunity
Opportunity sample is when you take the sample from people who are available at the time
Advantages of opportunity sampling
-easy to carry out
-cheap
-no sampling frame is needed
Disadvantages of opportunity sample
-unlikely to provide a representative sample
-highly dependent on individual researcher
Quota sample: non-random sampling
A quota sample is when an interviewer selects a sample that reflects the characteristics of the whole population.
Advantages of a quota sample
Quota sampling allows a small sample to still be representative of the population
-no sampling frame is required for quota sampling
-quick, easy cheap
-allows for easy comparison between different groups within a population
Disadvantages of a quota sample
-non random sampling can introduce bias
population mut be divided into groups which is costly and inaccurate.
-increasing scope of study increases number of groups which adds time and expense
-non-responses are not recorded
