Groups of ppts that form the research process are selected through what process?
Sampling
Define population
Group of people who the researcher is interested in studying
What is the researcher’s population often called?
Target population - a subset of the general population
Define sample
A group of people who take part in an investigation - drawn from the target population and presumed to be representative
Why should the sample drawn from the target population be representative?
To be able to generalise findings
How are samples selected?
Via sampling techniques
What are the 5 types of sampling techniques?
Random sample
Systematic sample
Stratified sample
Opportunity sample
Volunteer sample
What is a random sample?
All members of target population have equal chance of being selected
Need to obtain complete list of all members of TP - then all names are assigned a number
Sample selected through lottery method to ensure it is random
What is a systematic sample?
When every Nth member of the TP is selected e.g. every 5th pupil on a school register
Sampling frame is produced - a list of people in TP organised into an order e.g. alphabetical
Sampling system is nominated (e.g. every 5th)
Can begin from a randomly determined start to reduce bias
Researcher works through sampling frame until sample is selected
What is a stratified sample?
The composition of sample reflects the proportions of certain subgroups within the TP via strata
Researcher identifies the different strata that make up the population
Work out proportions needed for sample to be representative
Ppts that make up each stratum are selected using random sampling
What is an opportunity sample?
Researchers select anyone who is willing & available
Takes chance to ask whoever is around at time of study
What is a volunteer sample?
Ppts self select themselves to be part of the sample (self selection)
Researcher might place advert
Those who self select themselves would then make up the sample
What are the evaluation points for random sampling technique?
Potentially unbiased - confounding variables equally divided between the groups enhancing internal validity
Difficult & time consuming to conduct - list of TP may be difficult to obtain
Can still end up with a unrepresentative sample - never certain
What are the evaluation points for systematic sampling technique?
Objective method - little room for bias : researcher has no influence over who’s chosen once system for selection has been established
Method is time consuming & ppts can refuse to take part
What are the evaluation points for stratified sampling technique?
Can generalise findings as it produces a representative sample - designed to reflect the composition of the population
Identified strata might not always reflect the TP accurately - there isn’t complete representation
What are the evaluation points for opportunity sampling technique?
Convenient & less costly e.g. no list required
Suffer from 2 types of bias : sample is unrepresentative as it’s drawn from specific area (can’t be generalised to TP) & researcher has complete control over selection of ppts (researcher bias)
What are the evaluation points for volunteer sampling technique?
Convenient & less time consuming - requires minimal input from researcher
Volunteer bias - those who volunteer may have a certain ‘profile’ e.g. curious/pleasing. This can then affect how far the findings can be generalised