Types of experiments & sampling Flashcards
What is a laboratory experiment?
- An experiment that takes place in a controlled environment within which the researcher manipulates the IV and records the effect on the DV
Strengths of a laboratory experiment
- high control over confounding and extraneous variables
- can establish cause & effect (high internal validity)
- easy to replicate because of the high level of control e.g. standardisation
Weaknesses of a laboratory experiment
- high chance of demand characteristics
- lacks mundane realism (not like everyday experience)
- lacks generalisability (lab is artificial)
- low external validity
What is a field experiment?
- An experiment that takes place in a natural setting within which the researcher manipulates the IV and records effect on the DV
Strengths of a field experiment
- less chance of demand characteristics
- higher mundane realism
- high external validity (produces more valid and authentic behaviour)
Weaknesses of field experiments
- cause and effect difficult to establish due to loss of control of EVs and CVs (low internal validity)
- precise replication impossible
- ethical issues if participants are unaware they are being studied (cannot consent)
What is a natural experiment?
- An experiment where the change in IV is not brought about by the researcher
- The IV is naturally occurring and researcher records effect on the DV
Strenghts of a natural experiment
- provides opportunities for research that may not otherwise be undertaken for ethical or practical reasons
- high external validity (study of real world issues)
- less chance of demand characteristics
Weaknesses of a natural experiment
- naturally occurring events may happen rarely reducing opportunities for research
- low control over the EVs and CVs, cause & effect hard to establish - low internal validity
- cannot be replicated
What is a quasi experiment?
An experiment in which the IV is naturally occurring but is based on an existing difference between people (age, gender)
Strengths of a Quasi experiment
- high ecological/external validity- due to lack of involvement of researcher
> findings can be generalized to real-life settings
Weakenesses of quasi experiment
- low internal validity - researcher cannot accurately assess affect on DV due to lack of control of EVs and DVs
- not replicable- due to researchers lack of control so reliability cannot be assessed
What is meant by term population?
- A large group of individuals that a researcher is interested in studying
What is meant by the term sample?
- A smaller group of individuals drawn from a target population and are representative of that population
What is random sampling?
- form of sampling which all members of target population have a equal chance of being selected
How to get a random sample?
- obtain list of all members of target population
- assign names on the list with a number
- select sample through use of the lottery method ( names in hat, random generator etc)
What is systematic sampling?
- form of sampling when every nth member of the target population is selected
How to obtain a systematic sample?
- list of people in target population organised e.g. alphabetical order
- choose sampling system ( every 6th, 3rd etc)
- work through list until full sample complete
What is stratified sampling?
- sophisticated form of sampling in which researchers first divide a population into smaller subgroups, or strata (shared characteristics) and then randomly select among each stratum in the proportion they occur in the population to form the final sample
How to obtain a stratified sample?
- researcher identifies different strata that make up the population
- select sample from each strata (random) in the same proportion they occur in the population ( work this out)
What is opportunity sampling?
- researchers decide to selects anyone who happens to be willing and available
How to obtain a opportunity sample?
- researcher asks whoever is around at the time of the study
What is volunteer sampling?
- participants select themeselves to be part of the sample- self-selection
How to obtain a volunteer sample?
- reseacher places an advert in a newspaper or notice board
strengths of random sampling
- free from bias from researcher part
- produces representative samples
- everyone has an equal chance of being selected
Weaknesses of random sampling
- difficult and time consuming to conduct (list)
- small minority groups may distort results
- selected participants may refuse to take part
Strengths of systematic sampling
- free from bias, hence likely to be representative
- can generalize results
Weaknesses of systematic sampling
- method is time consuming
- those selected may refuse to take part
- by chance it could generate a biased sample ( periodic traits)
Strengths of stratified sampling
- more representative than other methods > due to proportional representation
- can generalize results
Weakness of stratified sampling
- more time consuming than other methods as you have to identify subgroups
- stratification is not perfect- cannot reflect all ways people are different
Strengths of opportunity sampling
- Quick and convenient
- less costly
Weaknesses of opportunity sampling
- researcher bias as they choose so may avoid certain people
- sample is unrepresentative of target population as it is drawn from specific area
Strengths of volunteer sampling
- quick and easy as it requires minimal effort from researcher
- less time consuming than other forms
- attract participants who are more engaged
Weaknesses of volunteer sampling
- volunteer bias, may attract a certain type of person e.g. more confident
- hard to generalize due to bias
