Causality
The primary goal of science is to establish a cause and effect relationships
A causes B to...
A is the independent variable
the variable being manipulated to hopefully result in a cause and effect relationship with the dependent variable
B is the dependent variable
the variable being tested to see the effect of the independent variable
The establish causality an experiment is needed
The Experiment
Control over A ( the independent variable )
We get control by creating different groups to compare against each other
Typically an experimental group and a control group
both groups are treated the same except one has the independent variable that is manipulated
Control over confounding variables
We get control over the variables that can interfere with the experiment causing false results by random assignment
We measure the dependent/outcome variable of every subject
Random Assignment as a control for A
To control for the independent variable by way of random assignment, we make sure the groups are equal to each other prior to the treatment.
this allows the researcher to attribute any change to the manipulation of the independent variable
Meanings of control
control over Independent variable
control over the environment
Any other attempt made to eliminate the influence of a threat to a casual inference
Problems with experiments
Can't be used to answer every question
Are not natural
Unable to control for everything
Options other than a tradition experiment
quasi-experiment
no control over independent variable
Correlational study
only looks at the relationship between variables
no cause and effect relationip ( causality )
The importance of this is for Validity
Validity equals to the accuracy of the experiment or study
determines whether the question you asked was correct or not
Two main types:
Internal validity : the degree to which the results are attributed to the independent variable and not some other rival explantion
External validity : the extent to which the results are generalizable
Reliability
An experiment cannot be valid if it is not reliable
reliability is the relative consistency of test scores and other educational and psychological measures
however, no measurement is perfect
ultimately becomes an issue of validity
Reliability of Measures
This refers to whether the measures used actually measure what is being tested consistently
Internal consistency/reliability (Cronbach's alpha)
if the researcher does not provide the Cronbach's alpha that is not good
Poor test-retest performance (correlation)
Low inter-rater reliability (correlation)
multiple raters used
if there are not multiple raters that is not good
Alternate/parallel forms (correlation)
The reliability coefficient ( persons r )
.90+ = excellent
.80-.89 = good
.70-.79 = adequate
< .70 = may have limited applicability
Reliability of treatment implementation from participant to participant
Lack of standardization in the study protocol introduces the chance that observed covariation may not be related to treatment
If the groups are treated differently then the study won't be able to determine that the change is attributed to the manipulation of the IV
Any lack of control over test conditions increases the chance that observed covariation may not be related to treatment
If the groups are in different test conditions then the possible change cannot be attributed to the manipulation of the IV
examples:
lack of instructions/ delivery
test conditions not the same
Regression to the mean
Essentially means that things tend to even out over time
extreme scores are rare and usually flatten out after test-retest
This can be problematic when conditions of an experiment are based on the extreme scores
high and low IQ scores
Random heterogeneity of Participants
Individual differences of participants that are related the dependent variable that can cause issues
some participants might be more impacted by the treatment than others because of this
solutions:
use people from same groups ( homogenous)
i.e. college students, south, north
can be a disadvantage because results can't be generalized
Random assignment
within-subjects design
matching participants
