Research and Statistics

AP PSYCHOLOGY RESEARCH METHODS

Often times, though we think we know, we don’t really know everything we think we know……

Hindsight bias- the tendency to believe, after learning an outcome, that one would have foreseen it.

Judgmental Overconfidence- over tendency to believe we know more than we actually do

Setting up good SURVEYS

• Population- all the cases in a group being studied

• Random sample- a sample that fairly represents a population because each member has an equal chance of inclusion

• We must be careful to avoid bias when conducting research, especially in surveying. Bias can be found in the samples chosen or the questions being asked

Setting up good research

• Operational definition- a statement of the procedures used to define research variables

• Replication- repeating the essence of a research study to see whether or not a study’s basic findings extends to other participants and circumstances

Dr. Scientist

In Experimental Psychology….How do researchers attempt to prevent bias or inadvertent manipulation of data?

Random assignment- assigning participants to experimental & control groups by chance, thus minimizing preexisting differences between assignees.

• Experimental group• Control group

Double-blind procedure- an experimental procedure in which both the research participants and the research staff are ignorant about whether the participants have received the treatment or the placebo

Don’t forget those variables!• Independent variable

• Dependent variable

• Confounding variable- a factor other than the independent variable that might produce an effect in an experiment

Wilhelm Wundt agrees!

Stats is all Thatz!• Correlation- a measure of the extent to

which two factors vary together and thus how well either factor predicts the other.

• Correlation Coefficient- a statistical index of the relationship between 2 things.

(Measured from -1.0 to 1.0)

Yep, Stats is where it’s At’s!

Fun with Scatter plots!

Scatter plot with a positive correlation Scatter plot with a negative correlation

Measures of Central Tendency• Mode- the most frequently occurring score in a distribution

2, 3, 3, 3, 5, 6, 7, 8, 9

• Mean- the average of a distribution, obtained by adding the scores and then dividing by the number of scores

2, 3, 3, 3, 5, 6, 7, 8, 9

Mode =3

Mean =5.1

• Median- the middle score in a distribution 2, 3, 3, 3, 5, 6, 7, 8, 9

Median =5

Standard Deviation• A computed measure of how much scores vary around the mean score

In a normal distribution…….• Usually 68% of data falls within one standard deviation of the mean

• 95% of data generally fall within 2 standard deviations of the mean

• Few scores or pieces of data fall near the extremes

Einstein’s IQ was 160, 4 standard deviations from the mean!