Year 1 Stats Flashcards
(23 cards)
What is a population?
The whole set of items that are of interest
What is a sample?
A whole subset of the population intended to represent the population
What is a sampling unit?
Each individual thing in a population that can be sampled
What is a sampling frame?
The list of sample units that are numbered
What is a census?
Data collected from an entire population
What is the advantage of using a census instead of a sample?
Should give a completely accurate result
What is the advantage of using a sample instead of a census?
Cheaper, quicker, less data to process
State the types of random sampling
Simple random sampling
Systemic sampling
Stratified sampling
State the types of non-random sampling
Quota sampling
Opportunity/convenience sampling
What is random sampling?
Having each sampling unit in a sampling frame having an equal chance of being chosen, in order to avoid bias
What is simple random sampling?
Every sampling unit in the sampling frame has an equal chance of being selected
How do you carry out simple random sampling?
In a sampling frame, give each item an identifying number, and select your samples using a random number generator
What are the advantages of simple random sampling?
-Bias free
-Easy and cheap
What are the disadvantages of simple random sampling?
-Not suitable when population size is large
-Sampling frame needed
What is systematic sampling?
Required elements are chosen at regular intervals in an ordered list
How is systematic sampling carried out?
Take every kth element. K = population size / sample size
Start at a random item between 1 and k and go from there, picking every kth person
What are the advantages of systematic sampling?
-Simple and quick
-Suitable for large samples/populations
What are the disadvantages of systematic sampling?
-Sampling frame needed
-Can introduce bias if the sampling frame isn’t random
What is stratified sampling?
-Population is divided into groups, and a simple random sample is carried out in each group
-Used when a sample is large and population naturally divides into groups
How do you calculate what proportion to use for each group in stratified sampling?
Sample size / population size = the percentage of each group to use.
What are the advantages of stratified sampling?
-Reflects population structure
-Guarantees proportional representation of groups within population
What are the disadvantages of stratified sampling?
-Population must be clearly classified into distinct strata
-Sampling frame needed per strata (group)
What is a strata?
A group within a population you want to sample
