Correlation and Experiments

(Cont. of Psychology is a science.)Chapter 1 – Myers

Chapter 2 – Barron’s

Review – Last class

• Descriptive Methods • Case Study• Survey• Naturalistic Observation

Correlation

• Correlation – measures the relationship between two variables

• Correlation coefficient: a statistical measure of the extent to which two factors vary together, and thus of how well either factor predicts the other. A correlation means that there is an association between two factors.

Examples of Correlations• Ex. of some correlations

• Thin people live longer• Overweight people earn less money than their

peers

• School uniforms decrease school violence • Handedness (L or R) and driving skills• Juvenille Delinquincy and growing up in a

single parent home• The Marshmallow Experiment & Time • Oh, The Temptation

Correlation

• The correlation coefficient shows two aspects of a relationship• Direction (Positive or negative)• Strength (how close to 1.00 OR -1.00)

• Correlation coefficients range between -1.00 and +1.00

• Number shows Strength• + or – shows Direction

• Positive – direct relationship • Negative – inverse relationship• Exercise on this AND Live!Psych

Correlation Coefficient

CorrelationCoefficients

Explanation

+ 1.00 Perfect positive correlation – an increase in one factor will always be matched by an equal increase in the other factor.

+ 0.50 Positive correlation – as one factor increases the second factor tends to increase. (Can range from +0.99 to +0.01)

0.00 Zero correlation – no relationship between the two factors. This is the weakest possible correlation.

- 0.50 Negative correlation – as one factor tends to increase, the second factor tends to decrease.

- 1.00 Perfect negative correlation – an increase in one factor will always be matched by an equal decrease in the other factor.

Correlation and Causation

• Correlation does NOT prove causation• Correlation indicates the possibility of a cause

and effect relationship• Correlation may be due to coincidence• Ex. Ice Cream consumption and rapes.• Correlation may be due to other factors

(confounding variables).

Q Correlation between juvenille delinquincy and growing up in a single parent home?

Illusory Correlations

• Illusory Correlations: the perception of a relationship where none exists

• When I wash my car, it always rains• As the number of ice cream sales increases,

the number of murders increases • Those who adopt a child are more likely to

conceive.

Experiments

• Experiment – a research method is one which an investigator manipulates one or more factors (IV) to observe/measure the effect of some behavior or mental process (DV). Only experiments can identify cause and effect relationships

Experimental Conditions

• Experimental condition – to expose a participant to treatment (Ex. pill increase focus when taking tests).

• Control condition – contrast to the experimental condition. Serves as a comparison in that this subject does not receive treatment OR receives a placebo.

• Confounding variable – any difference between the experimental and control conditions, except for the independent variable. One can control for confounding variables by random assignment. Exercise: Ruler Experiment

Random Assignment

• Random Assignment (ONLY Used in the experimental method) is the process by which subjects are placed into an experimental or control group. Random assignment limits the effect of subject-relevant confounding variables. (outside factors of the subject other than the IV).

Controlling for all other variables

• Equivalent environments control for situation-relevant confounding variables.• Room temperature, test administrator with a cold

• Random assignment controls for subject-relevant confounding variables. • What if each student got to pick the group in which

he/she wanted to take part?

• Experimenter bias (when the experiment wants or expects certain results) can be eliminated by using double blind procedure.

Variables• Independent Variable – the experimental factor

that is manipulated. This is the variable being studied.

• Dependent variable – the experimental factor that is being measured. This is the behavior or the mental process. This variable may change depending on manipulations in the IV.

• Live Psych slides 3 (IV and DV) and 5.(Op def.)

IV and DV

•If one receives more sleep before a test he/she performs better• IV – Sleep• DV – Test Scores

•Does the use of color of a football jersey affect perception of referees.

• IV – watching football plays with a team wearing black• DV – amount of penalties called.

• Activity: Hunting for Causes

Example Experiment

• Hypothesis – This pill will lower hyperactivity in children with ADHD

• Independent Variable – receiving the pill• Dependent Variable – level of hyperactivity• Experiment Design - Students with ADHD

are randomly assigned to a group. Exp. Group receives pill while the control group receives a placebo (fake pill). A month later students level of hyperactivity is measured

Double Blind• Blind – unaware of what treatment is

received• Double Blind - participants and research

staff are ignorant about the treatment/placebo given to each subject. Double blind procedures can eliminate subject and experimenter bias.

• Why could this be beneficial in a study? • Research expectations can also affect how a patient

acts/reacts to certain treatment• Essential in drug research to control for self-fulfilling

prophecies, placebo effects, or biases from the experimenters.

Methods of Eliminating Bias

• Random Sample

• Random Assignment

• Placebo (if a experiment is drug related)

• Double Blind

• Replication

Placebo Effect• Placebo Effect - results caused by expectations

alone. • Using a Placebo - One group receives the treatment

(drug being tested) the other receives a pseudo treatment (placebo).

• Ex. In the Korean War patients were given placebos when they ran out of morphine. Most patients reported a reduction in pain.

• Ex. College freshman were given 6 non-alcoholic beers to drink in 2 hours. Most exhibited some intoxicating behaviors.

• Penn and Teller: Placebo Effect

Hawthorne Effect• Research in which workers were monitored to

see if the amount of light in a room would affect worker productivity.

• Under both conditions, performance increased because subjects were being watched.

• The Hawthorne Effect states that people tend to act atypical having been chosen for an experiment.

• The Hawthorne Effect complicates experiment design

Experiments aim to ….

• MANIPULATE the IV

• MEASURE the DV

• CONTROL for all other factors through random sampling

• Prove a CAUSE AND EFFECT relationship

Correlation vs. Experiment

• In pairs (or by yourself), state whether research is correlational or experimental. If it’s correlational state whether it’s positive or negative. If it’s experimental state the IV and the DV.