Sampling Flashcards
What is a population?
A group of people who are the focus of the researchers interest, from which a smaller sample is drawn.
What is a sample?
A group of people who take part in a research investigation. The sample is presumed to be representative of the population.
Why do we need to take a sample?
For practical and economic reasons it is usually not possible to include all members of a target population in an investigation so the researcher selects a small group.
What is random sampling?
A form of sampling in which all members of a target population have an equal chance of being selected.
How is random sampling done?
1) Obtain a list of all members of the target population.
2) The names are all assigned a number.
3) The sample is chosen through the use of some lottery method e.g a random number generator or picking numbers out of a hat.
Strength of a random sample.
Potentially unbiased so that confounding or extraneous variables should be equally divided between the different groups, enhancing internal validity.
Limitations of random sampling.
-difficult and time-consuming to conduct. A complete list of the target population may be difficult to obtain and will take lots of time.
-Sample still may be unrepresentative.
-Participants may still refuse to take part which means you’ll end up with something like a volunteer sample.
What is a systematic sample?
Every nth number of the target population is selected. E.g every 5th pupil on a school register.
Strength of systematic sampling.
-objective as the system for selection has been established prior so the researcher has no influence over who is chosen.
Limitation of systematic sampling.
Time-consuming and in the end participants may refuse to take part resulting in a volunteer sampling.
What is a stratified sample?
The composition of the sample reflects the proportions of people in certain subgroups within the target population or wider population.
The researcher identifies the different strata which make up the population. Then the proportions needed for the sample to be representative are worked out. Finally the participants that make up each stratum are selected via random sampling.
Strength of stratified sampling.
Produces a representative sample because it is designed to accurately reflect the composition of the population.
Limitation of stratified sampling.
Stratification is not perfect. The identified strata cannot reflect all the ways that people are different so a complete representation of the target population is not possible.
What is opportunity sampling?
Many researchers simply decide to select anyone who happens to be available at that time to take part in the experiment.
Strength of opportunity sampling.
The method is convenient as it much less costly in terms of time and money because listing the members of the target population is not necessary.
