Psych Chapter 10
Psychologist Andrew Elliot wanted to test whether the color red impacted performance on a test
The theory was based on an approach/avoid orientation in achievement
Approach – strive to get answers right; excited about challenge
Avoid – try not to fail; anxiety
Tested with an Experiment:
71 students in a lab
5-minute test unscrambling anagrams
Identical tests except that the student ID numbers were written in either red, green or black ink on the inside of the test booklet
Students were randomly assigned to the conditions
Students at Cornell University’s Food and Brand Lab were studied
Randomly assigned to a large bowl and medium bowl condition
Participants who served themselves from a large bowl took more and ate more, compared to those who served themselves from a medium bowl.
The covariance was explained by the difference in means of the two groups.
YOU NEED COMPARISON GROUPS
The cause comes before the effect
Better then a correlational study where the variables are measured at the same time
Allows us to rule out other explanations for the change in the dependent variable
For example: In the Elliott anagram experiment to rule out other explanations for the difference in performance the researchers made sure that all conditions – the anagrams, the researchers attitudes, the test forms, even which condition the participants were in was unknown to the researcher – were kept the same
ex. , if Elliot had given the red ink group more difficult anagrams than the other groups the difficulty of the test would have been a design confound
Does not harm internal validity but can cause other issues
Can happen then participants are allowed to choose which condition that they want to be in
One-on-one sessions with a therapist for 40 hours per week
Some children received new treatment, some their standard treatment
Families allowed to select condition
Clear selection effect – families who are willing to devote 40 hours are probably working more with their children
Selection is a clear confound in this instance
Also called between-subjects and between-groups designs
Also called within-subjects design
In some situations, like the pasta experiment, a pre-test is not possible
Random assignment helps ensure that confounding variables are evenly distributed between groups – like appetite
Babies saw two faces simultaneously, and the experimenters recorded which face they looked at the longest.
Oxytocin is a bio-chemical thought to be important in social bonding. Mothers oxytocin levels were measured with their own 2 or 3 year old toddlers and then again several days later with another infant. Levels were found to be higher with the new toddler.
Cons: Require more people
Individuals serve as their own control
Cons: Potential order effects, chance of experimental demand
within-groups have more power
Noisy party – makes it hard to hear conversations even when they are going on
major threat to internal validity: order effects
Also called practice effects or carryover effects
2. People can change their behavior depending on exposure to previous conditions
2a. Could be demand conditions – participants try to act like “good participants”
3. Within-groups design might not be possible – two methods of training someone to ride a bike, cannot un-teach a person how to ride a bike
– Is the measure a good representation of the construct of interest?
– How well was the independent variable manipulated?
– The standard is typically the theory that the researcher is testing
– For the experiment about color and avoidance orientation, critics could argue that the experiment came out the way that it did because the color red is a warm color, not a threat. So Elliot and colleagues added a warm color – orange – to improve construct validity
– Generalizing to other people – random sampling versus random assignment
– Generalizing to other situations – takes more than 1 study to generalize
Are the results statistically significant?
What is the effect size?
– This is the most important validity for experiments!
– Three fundamental internal validity questions:
1. Did the design ensure that there were no design confounds?
2. If an independent-groups design was used, were selection effects controlled for by random assignment or matching?
3. If a within-groups design was used were order effects controlled for by counterbalancing?