Techniques Used to Get Unbiased Samples

This sample consists of the entire population

• convenience
• census
• cluster
• simple

This sample consists of units of the population that are easily accessible.

• Cluster
• Convenience
• Volunteer
• Observational

This sample consists of units of the population that chose to respond.

• mandatory
• census
• volunteer
• unbiased

Every possible group of units of the required size has the same chance of being the selected sample as any other sample of the same size.

• Simple Random 
• Thoughtful
• Typical
• Proportional

This sample is selected by dividing the population into subgroups and then taking a fixed number of units from each group using the simple random sample.

• stratified
• cluster
• judgment
• experimental

Units of the population are ordered in some fashion.  Usually, every k-th unit is chosen.

• proportional
• probable
• stratified
• systematic

This method produces values that systematically differ from the population being sampled.

• valid sample
• variable sample
• biased sample
• cluster sample

Units of the population are grouped; one or more groups are selected at random.  All units of that group are included in the sample.

• cluster sample
• simple random
• stratified
• proportional

The conductor has no input or control over the environment in this situation

• census
• observational study
• experiment
• judgment

Cluster, stratified, simple random, systematic, and proportional are all types of 

• convenience samples
• biased samples
• haphazard samples
• unbiased samples