Stats

What is a population in statistics?

The whole set of items or individuals that are of interest in a study.

What is a sample?

A subset of the population used to estimate characteristics of the whole population.

What is a census?

Collecting data from every member of the population.

What are sampling units?

Individual members of the population being studied.

What is a sampling frame?

A complete list of all sampling units in the population.

One advantage of a census

Gives a completely accurate result since every member is measured.

One disadvantage of a census

Time-consuming and expensive.

Why might a census be impossible in some cases?

If the testing process destroys the item.

One advantage of using a sample instead of a census

Faster and cheaper.

Another advantage of sampling

Less data to process.

One disadvantage of using a sample

Results may not be as accurate as a census.

Another disadvantage of a sample

It may not represent small subgroups of the population.

What is simple random sampling?

A sampling method where every sample of size n has an equal chance of being selected.

First step of simple random sampling

Create a sampling frame.

How are individuals chosen in simple random sampling?

Using random numbers.

One advantage of simple random sampling

Free from bias.

Another advantage of simple random sampling

Each unit has an equal probability of selection.

One disadvantage of simple random sampling

Requires a sampling frame.

Another disadvantage of simple random sampling

Difficult to use for very large populations.

What is systematic sampling?

Selecting items at regular intervals from an ordered list.

How do you calculate the sampling interval?

Population size ÷ sample size.

One advantage of systematic sampling

Simple and quick to use.

Another advantage of systematic sampling

Suitable for large samples.

One disadvantage of systematic sampling

Requires a sampling frame.

Another disadvantage of systematic sampling

Can introduce bias if the list has a pattern.

What is stratified sampling?

Dividing the population into groups (strata) and randomly sampling from each group.

What must strata be?

Mutually exclusive groups.

Formula for stratified sampling size

(Number in stratum ÷ population) × sample size.

One advantage of stratified sampling

Accurately reflects the population structure.

Another advantage of stratified sampling

Ensures proportional representation.

One disadvantage of stratified sampling

Population must be clearly divided into strata.

Another disadvantage of stratified sampling

Sampling within strata has similar issues as simple random sampling.

What is quota sampling?

Researchers select participants to match population characteristics.

One advantage of quota sampling

No sampling frame required.

Another advantage of quota sampling

Quick and inexpensive.

One disadvantage of quota sampling

Non-random sampling can cause bias.

What is opportunity sampling?

Sampling people who are available at the time of the study.

One advantage of opportunity sampling

Very easy to carry out.

Another advantage of opportunity sampling

Low cost.

One disadvantage of opportunity sampling

Not representative of the population.

Another disadvantage of opportunity sampling

Results depend heavily on the researcher.

What is quantitative data?

Numerical data.

What is qualitative data?

Non-numerical data describing qualities or categories.

What is continuous data?

Data that can take any value within a range.

What is discrete data?

Data that can only take specific values.