Psychological Research Methods and Statistics

M&M Sampling Activity Central tendency- A number that describes something about the “average” score of a distribution Range- a measure of difference, or spread of data, aka variability Statistical significance- evaluates the likelihood that results were due to chance - limit is set by researcher -If researcher says the probability that their results were due to chance is less than 1-5% (0.01-0.05), it is considered statistically significant

PRE-RESEARCH DECISIONS SAMPLE- a small group of participants, out of the total available, that a researcher studies Must be representative by random sample or stratified sample

RANDOM VS. STRATIFIED SAMPLE *STRATIFIED SAMPLE: representative of various subgroups of the population People are put into mutually exclusive, non-overlapping groups, then chosen randomly from each group. Each group is represented in final sample. *RANDOM SAMPLE: everyone has an equal chance of being picked

TYPES OF RESEARCH

TYPES OF RESEARCH *NATURALISTIC OBSERVATION- observe the subject in a natural setting without interfering *CASE STUDY- intensive investigation of one or more participants good for descriptive material that can create new hypotheses *SURVEYS- information obtained by asking many individuals a fixed set of questions interviews or questionnaires

TYPES OF RESEARCH cont’d *LONGITUDINAL STUDIES- data are collected about a group of participants over a number of years to assess how certain characteristics change or remain the same during development *CROSS-SECTIONAL STUDIES- data are collected from groups of participants of different ages and compared so that conclusions can be drawn about differences due to age

TYPES OF RESEARCH cont’d *CORRELATIONS AND EXPLANATIONS- to measure the relationship between two variables or sets of data *Describes but no causation *EXPERIMENTS- show causation

SCIENTIFIC EXPERIMENTATION

SCIENTIFIC EXPERIMENTATION HYPOTHESIS - a statement or testable prediction about the relationship between two variables *INDEPENDENT VARIABLE (I.V.) - the variable that is manipulated in an experiment; applied to the experimental group *DEPENDENT VARIABLE (D.V.)- the variable that is measured to see how it changed in an experiment CONTROL GROUP- group that is treated the same way as the experimental group except that the experimental treatment is not applied

EXPERIMENTATION CONT’D *EXPERIMENTAL GROUP- in a controlled experiment, the group that is subjected to a change in the I.V. *CONTROL GROUP - in a controlled experiment, the group not subjected to a change in the I.V. (used for comparison) RESULTS - Did I prove or disprove my hypothesis?

THINGS TO BE CONSIDERED WHEN CONDUCTING AN EXPERIMENT *CONFOUNDING VARIABLES - variables that you cannot control for ETHICAL CONSIDERATIONS - APA The Milgram Experiment EXPERIMENTER BIAS- expectations of the experimenter that might influence the results of an experiment PLACEBO EFFECT - when a person believes that a pill or procedure without medicinal value will reduce pain

SELF-FULFILLING PROPHECY *A situation in which a researcher’s expectations influence that person’s own behavior and thereby influence the participant’s behavior TO AVOID *SINGLE-BLIND EXPERIMENT- participants are unaware of which participants received the treatment *DOUBLE-BLIND EXPERIMENT- neither the experimenter nor the participant know which participants received which treatment

EXPERIMENTAL STATISTICS

STATISTICS *DESCRIPTIVE STATISTICS- listing and summarizing the data in a practical, efficient way FREQUENCY DISTRIBUTION- an arrangement of data that indicates how often a particular score or observation occurs

STATISTICS *NORMAL CURVE- bell-shaped, symmetrical frequency distribution graph of normally distributed data

CENTRAL TENDENCY *A number that describes something about the “average” score of a distribution Mean, median, mode

MEASURES OF VARIABILITY VARIABILITY- a measure of difference, or spread of data; aka the range STANDARD DEVIATION- a measure of variability that describes the average distance of every score from the mean Scores above the mean will have a positive deviation, below will have a negative deviation If distribution is spread out, deviation is large; if bunched up, it is small

STANDARD DEVIATION

CORRELATION COEFFICIENTS *Describes the direction and strength of the relationship between two sets of variables *Correlation is the degree of relatedness Usually the Pearson correlation coefficient r (+) indicates positive (-) indicates inverse/negative relationships From -1 to +1 ± 0.60 to ±1.0 is strong ±0.30 to ± 0.60 is moderate 0 to ± 0.30 is weak 1 is a perfect correlation and rare

INFERENTIAL STATISTICS *Numerical methods used to determine whether research data support a hypothesis or whether results were due to chance *STATISTICAL SIGNIFICANCE- evaluates the likelihood that results were due to chance Limit is set by researcher If researcher says the probability that their results were due to chance is less than 1-5% (0.01-0.05), it is considered statistically significant

C lunch tomorrow

HOMEWORK Watch the news one night. Write down any statistics that the media uses and how they are used.

Wednesday Find out more information on your assigned experiment. Summarize in bullet points, diagrams, pictures, charts what the experiment did Read through the APA ethical codes/guidelines Determine and write down on your poster what codes your experiment violated Explain what the experimenters should have done to avoid violating codes Be prepared to explain this all to the class

Warm-Up: HOMEWORK FROM NEWS For each statistic, do you feel that enough information was provided to evaluate the validity of any reported claims? What other information should have been provided? How might additional information change the reported conclusions?

I’M A PSYCHIC How could this be performed without psychic abilities? Write a hypothesis and design an experiment for testing it (using research terminology).

MAGIC A well-known psychic sometimes begins his performance by saying the following: “Think of a number between 1 and 50. Both digits must be odd numbers, but they must not be the same. For example, it could be 15, but could not be 11. Please choose a number and I will tell you what number you are thinking of.” Develop a hypothesis that explains how the psychic is performing this feat. (Hint: The psychic uses statistics, not magic.) Based on the psychic’s directions, decide which numbers can be used and which numbers will most likely be used. How do your observations support or contradict your hypothesis?