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Independent vs. dependent variable

(IV) - what the researcher manipulates
(DV) - what the researcher is measuring

Categorical variable


Null vs. research hypothesis

null: proposes no relationship & difference between the two variables. We predict no relationship between x and y. (example: the level of noise has no effect on one's test scores in mathematics.)

research: proposes a relationship between variables (the louder the noise, the lower the test score)


x does not cause y but x and y seem to always be together
-we cant tell if one thing causes another

Bidirectional ambiguity

does x cause y or does y cause x or neither

Construct validity

it is the extent to which what was to be measured was actually measured

Ecological validity

The study represents what happens in real life.


Revealing of and justifying aim and purpose of the research collected. This must be done at the end of all studies.

Repeated measures design

uses the SAME SUBJECTS in each condition of the experiment (ex: driving test w/ alcohol and later w/out)

-subject variables kept constant/same
-better statistical tests
-fewer subjects

-order effects (learning, fatigue, boredom)
-demand characteristics (refer to Psych 1 Aug.29-Sept.2)
-different tests may be needed

Independent samples design

uses DIFFERENT SUBJECTS in each condition of the experiment (ex: 1 driving test w/out alcohol then diff. group for a test w/ alcohol)

-order effects don't have an influence
-demand characteristics
-the same test can be used

-subject variables differ
-worse statistical tests
-more subjects required

Random sample

one in which every member of the target population has an equal chance of being selected. (classroom: sorting 1 person out of hat)

Sample of opportunity

already is there (ex: a class in school at the time of the study).
sample of people that is available at the time

Haphazard sample

interviewer arbitrarily selects people for survey
(ex: collecting people on the street)

Purposive sample

select people based on the purpose of the study/a focus a person has (ex: do you take cocaine?)

Stratisfied sample

sample that reflects the population
-what you do/are (you are Argentinian)

Self-selected sample

people volunteer/select themselves for the survey

Snowball (network) sample

when you use one member of sample to help you find other members of sample (trust gaining)

(ex: talk to 1 drug dealer & gain his/her trust & ask him/her to introduce you to more drug dealers)

Expectancy effect

- ?

Demand characteristics

participant acts differently because he/she knows they are in an experiment or what experiment he/she is in
(the participants want to help the researcher so he/she answers accordingly)


Laboratory environments and operationalized variables may lack ecological variability (DOUBLE CHECK THIS)


-definition: ?
-Example: One class takes a test and then a person who has just taken the test tells another class what is on the test, thus affecting the test results

Maturation (order effects)

the order you choose may affect experiment (play a game 3 times, you get better at it by the 3rd time)

Confounding variables

a variable you should have controlled but didn't

Intervening variables

variables over which you have no control and which negatively impact your experiment

Informed consent

Participants must be informed about the nature of the study and agree to participate.

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