Investigation question
● E.g. Does consuming sugar affect attention in children?
Hypothesis
Controlled experiment
● an investigation methodology that aims to test the effects of an IV on a DV, with all
other variables controlled
Extraneous variables
● may have an unwanted effect on the dependent variable and results of an
investigation
● should be controlled to not affect the internal validity of the investigation
results by becoming a confounding variable.
Controlled variables
● a variable that is held constant to ensure that the only influence on the dependent
variable is the independent variable
Confounding variables
● an unwanted variable that has affected the results of an investigation
● interferes with the internal validity of the investigation by providing
alternative explanations for the investigation results
Sampling techniques
Random sampling
● selecting participants from the population in a way that means each member of the
population has an equal chance of being selected to participate in the study
● Strengths → A large enough random sample is probably representative of the
population, improving external validity
● Allows for results to be generalised
, ● Limitations → Small random samples may not be representative of the population,
reducing the external validity, and it may be difficult, time consuming, impossible or
unethical to obtain names of all members of the population
Stratified sampling
● first dividing the population into subgroups, and then randomly selecting
participants from each subgroup in the proportion that they appear in the
population
● Strengths → A large enough stratified sample is probably representative of the
population, improving external validity, and important subgroups of a population are
ensured fair representation
● Limitations → It may be difficult, impossible or unethical to obtain names of all
members of the population, and it is more time consuming than using a random
sampling technique because of the need to form subgroups and any pre-testing
required
Convenience sampling
● is a quick and inexpensive way for a researcher to select a sample. However,
the sample may not be representative of the population
● results cannot be generalised
Random allocation
● dividing a sample into groups in such a way that each participant has an equal
chance of being placed into the experimental group or the control group
● helps to eliminate confounding variables
Groups
● Experimental group → the group that is exposed to the independent variable and
receives the experimental treatment
● Control group → the group that forms a baseline level to compare the experimental
group with
● E.g. Does consuming sugar affect attention in children?
Hypothesis
Controlled experiment
● an investigation methodology that aims to test the effects of an IV on a DV, with all
other variables controlled
Extraneous variables
● may have an unwanted effect on the dependent variable and results of an
investigation
● should be controlled to not affect the internal validity of the investigation
results by becoming a confounding variable.
Controlled variables
● a variable that is held constant to ensure that the only influence on the dependent
variable is the independent variable
Confounding variables
● an unwanted variable that has affected the results of an investigation
● interferes with the internal validity of the investigation by providing
alternative explanations for the investigation results
Sampling techniques
Random sampling
● selecting participants from the population in a way that means each member of the
population has an equal chance of being selected to participate in the study
● Strengths → A large enough random sample is probably representative of the
population, improving external validity
● Allows for results to be generalised
, ● Limitations → Small random samples may not be representative of the population,
reducing the external validity, and it may be difficult, time consuming, impossible or
unethical to obtain names of all members of the population
Stratified sampling
● first dividing the population into subgroups, and then randomly selecting
participants from each subgroup in the proportion that they appear in the
population
● Strengths → A large enough stratified sample is probably representative of the
population, improving external validity, and important subgroups of a population are
ensured fair representation
● Limitations → It may be difficult, impossible or unethical to obtain names of all
members of the population, and it is more time consuming than using a random
sampling technique because of the need to form subgroups and any pre-testing
required
Convenience sampling
● is a quick and inexpensive way for a researcher to select a sample. However,
the sample may not be representative of the population
● results cannot be generalised
Random allocation
● dividing a sample into groups in such a way that each participant has an equal
chance of being placed into the experimental group or the control group
● helps to eliminate confounding variables
Groups
● Experimental group → the group that is exposed to the independent variable and
receives the experimental treatment
● Control group → the group that forms a baseline level to compare the experimental
group with
