Statistics Chapter 1 Flashcards
What is a population?
A population is the whole set of items that are of interest.
What is a census?
A census measures every member of a population
What is a sample?
A sample is a selection of observations taken from a subset of the population which used to find out information about the population as a whole
What are advantages and disadvantages of a Census?
Advantages- •it should give a completely accurate result
Disadvantages- •Time consuming and expensive ,
•Cannot be used when the testing process destroys the item,
•hard to process large quantities of data
What are advantages and disadvantages of a sample?
Advantages - •less time consuming and expensive than a census
•Fewer people have to respond
•Less data to process than a census
Disadvantages-• The data may not be accurate
•The sample may not be large enough ro give information about small sub groups of the population
What is a sampling unit?
Individual units of a population
What is a sampling frame?
Population are individually named or numbered
What is simple random sampling?
A simple random sample of size ñ is one where every sample of size ñ has an equal chance of being selected.
What is systematic sampling?
In Systematic sampling, the required elements are chosen at regular intervals from an ordered list.
Interval = pop size / sample size
What is stratified sample?
the population is divided into mutually exclusive strata and a random sample is taken from each.
Number sampled in stratum = number in stratum / pop size * overall sample size
What are some 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 some disadvantages of simple random sampling
•Not suitable when the population size or the sample size is large as it is potentially time consuming,disruptive and expensive
•A sampling frame is needed
What are some advantages and disadvantages of systematic sampling?
Advantages- •simple and quick to use
•suitable for large samples and large populations
Disadvantages - •A sampling frame is needed
•it can introduce bias if the sampling frame is not random
What are some advantages of stratified sampling?
•Sample accurately reflects the population structure
•Guarantees proportional representation of groups within a population
What are some disadvantages of stratified sampling
•Population must be clear and classified into distinct strata
•Selection within each stratum suffers from the same disadvantages as simple random sampling
