Stats Chapter 1

What is a population?

The whole set of items that are of interest

What is a census?

Observers or measures every member of a population

What are sampling units?

Individual units of a population

What is a sample?

A selection of observations take from a subset of the population (to find out information about the population as a whole)

What is a sampling frame?

Sampling units of a population individually named and listed

What is a simple random sample of size n?

Every sample of size n has an equal chance of being selected

What is systematic sampling?

Required elements are chosen at regular intervals from an ordered list

What is stratified sampling?

Population is divided into mutually exclusive data strata and a random sample is taken from each (eg. male and female)

What is quota sampling?

Interviewer/researcher selects a sample that reflects the characteristics of the whole population

What is opportunity sampling?

Taking the sample from people that are available at the time and fit the criteria

What is quantitative data?

Data associated with numerical observations

What is qualitative data?

Data associated with non-numerical observations

What is continuous data?

Can take any value in a given range

What is discrete data?

Can only take specific values in a given range?

When are classes used?

When data is presented in a grouped frequency table and the specific values are not shown

What three things do classes tell us?

• Maximum and minimum that belong in each class

• Midpoint is the average of the class boundaries

• Class width is the difference between the upper and lower class boundaries

Give an advantage of using a census

It should give a completely accurate result

Give two disadvantages of using a census

• Time consuming and expensive

• Hard to process large quantity of data

Give two advantages of a sample

• Less time consuming and expensive than a census

• Less data to process than a census

Give two 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

Give two advantages of random sampling

• Free of bias

• Easy and cheap to implement

Give two disadvantages of random sampling

• A sampling frame is needed

• Not suitable for large population as it can be disruptive and time consuming

Give two advantages of systematic sampling

• Simple and quick

• Suitable for large populations/samples

Give two disadvantages of systematic sampling

• A sampling frame is needed

• Can introduce bias

Give two advantages of stratified sampling

• Accurately reflects population structure

• Guarantees proportional representation

Give two disadvantages of stratified sampling

• Population must be clearly stratified into distinct strata

• Selection within each strata suffers the same disadvantages as random sampling

Give two advantages of quota sampling

• Small sample still representative of population

• Quick, easy, inexpensive

Give two disadvantages of quota sampling

• Can introduce bias

• Population has to be divided into groups which can be costly or inaccurate

Give two advantages of opportunity sampling

• Easy to carry out

• Inexpensive

Give two disadvantages of opportunity sampling

• Unlikely to provide representative sample

• Highly dependent on individual researcher