# Quantitative Methods in Psychology by Levone

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```									Quantitative Methods in Psychology
Tom Cain - Tillett 629 01:830:200:B6 May 27 - July 2 MWF 6:00 - 9:40

Introduction
 Syllabus  Importance of coming to every class
Turn to chapter 12 in an intro. Book you haven‟t read, it will probably make sense. Turn to chapter 12 in stats. Book, it will likely be gibberish.

 Math phobia  Introductions from everyone
Year at Rutgers, major, age, gender, are you looking forward to this class?

Statistics
 We are almost speaking a different language in this class. If you learn the language, everything will make sense.  Statistics - a set of mathematical procedures for organizing, summarizing, and interpreting behavior
Organize and summarize information Answer questions based on the results obtained

Populations and Samples
 Population - all the individuals of interest in a particular study (characteristic that describes a population is called a parameter)  Sample - set of individuals selected from a population, usually intended to represent the population (characteristic that describes a sample is called a statistic)  Understanding the relationship between the population and a sample from that population is going to be a big part of this class  If we are mainly interested in the population, why don‟t we just study the population?

Variables and Data
 Variable - characteristic or condition that changes or has different values for different individuals  Data - measurements or observations (plural)
Data set - collection of measurements or observation Datum - single measurement (also called score or raw score)

Descriptive and Inferential Statistics
 Descriptive Statistics - statistical procedures used to summarize, organize, and simplify data  Inferential Statistics - techniques that allow us to study samples and then make generalizations about the populations from which they were selected  Sampling error - discrepancy that exists between a sample statistic and the corresponding population parameter

Research Methods
 Descriptive Research  Correlational Method - two different variables are observed to determine whether there is a relationship between them  Experimental Method - one variable is manipulated while another variable is observed and measured. Used to establish cause-and-effect relationship between variables

Descriptive Research
 Goal is to describe people and their thoughts, feelings, and behaviors.  Observational studies  Archival studies  Surveys
Random sample (nationally representative sampling) Unrepresentative samples (internet surveys?) Need to be aware of order of questions (order effects), response options, and the wording of questions

 We‟ll focus on two other methods:
Correlational designs Experimental designs

Correlational Designs
 Represents the strength of the relationship between two variables
e.g., # of hours of media exposure to violence & level of aggression e.g., certain illness and optimism/pessimism e.g., ability to delay gratification as a child and success in college

 Scatter plot  Correlation coefficient (“r”) ranges from -1 to +1
e.g., r = +.34 e.g., r = -.52

Interpreting Correlations
 Positive correlation
increase in exposure associated with increase in aggression

 Negative correlation
increase in exposure associated with decrease in aggression

 No correlation
Variables are not related

Correlations: Positive, Negative, and None

Correlation ≠ Causation

Why can‟t we infer causality?
 Reverse-Causality Problem
X→Y or Y ← X ????

Is there a relationship between exposure to violent TV and aggression?

Why can’t we infer causality?
 Reverse-Causality Problem
X→Y or Y ← X ????

 Third-variable problem
A→X and A → Y

e.g., ice cream sales and violence (r = +.29)

VERY IMPORTANT FOR INTERPRETING NEWS ABOUT HEALTH RESEARCH!!!

Explaining Correlations: Three Possibilities

 Allow assessment of behavior as it occurs in people‟s everyday lives
 Allow study of variables that can‟t be studied in experimental designs (e.g. smoking, cancer)  Establishes that a relationship between 2 variables exists  One very serious disadvantage
CORRELATION IS NOT CAUSATION!

Experimental Method
 Cornerstone of psychological research.  Used to examine cause-and-effect relationships.  Two essential characteristics:
Researcher has control over the experimental procedures to make sure that everything (but the variable being manipulated) stays the same. Researcher manipulates one variable by changing its value from one level to another. A second variable is observed (measured) to determine whether the manipulation causes changes to occur

 Participants are randomly assigned to different treatment conditions (they cannot self select).

 Participant Variables - things like gender, age, and intelligence. Vary from one individual to another  Environmental Variables - lighting, time of day, weather. Must be the same across conditions

Random Sampling vs. Random Assignment
 Random Sampling  Random Assignment

 Selecting Ps to be in study so that everyone in population has an equal chance of being in the study.
 Representative samples  Generalization  Is it possible?

 Assigning Ps (who are already in study) to the different conditions so that each P as equal chance of being in any of the conditions.
 Equalizes the conditions of experiment so that it is unlikely that conditions differ because of preexisting differences  Required for inferences of causality.

Variables
 Independent Variable
variable that we expect causes an outcome the antecedent event variable that the experimenter can control and manipulate

 Dependent Variable
the “effect” the outcome variable it‟s value depends on the changes introduced by the IV

IVs and Conditions
 Must have at least two conditions (also called “levels”) of the IV in order to demonstrate that the IV has an effect on the DV. Otherwise, it wouldn‟t be a „variable‟.  Experimental condition (IV present) vs. control condition (IV not present)
Those in control condition receive no treatment or receive neutral, placebo treatment. Provides baseline for comparison with experimental condition.

 Example interested in mood and helping  experimental group – told they received “A” or “F”  control group – does not grade feedback

Laboratory Experiments
 Conducted in settings in which: The environment can be controlled.  E.g., temperature, amount of light in room The participants can be carefully studied.  E.g., Ps remain in the same seat

Field Experiments
 Conducted in real-world settings.  Advantage: People are more likely to act naturally.  Disadvantage: Experimenter has less control (“quasi-experiments”).
Quasi-independent variable - independent variable in nonexperimental study. Typically something the experimenter cannot manipulate such as gender or smoking

Constructs & Operational Definitions
 Empirical Realization
translating the conceptual or abstract variables contained in your hypothesis to real, measurable constructs constructs – abstract level operational definition – The specific way in which a construct is manipulated or measured

Some exercises

Crusco & Wetzel (1984)
 interested in how touching influences individuals‟ perceptions of others  description of study
waitress performed normal duties when she gave change to customer, she approached the paying customer from the side, leaned forward, and w/out making eye contact, said in a friendly yet firm tone, “Here‟s your change.”
 1/3 – no touch control condition  1/3 – a brief hand-touch condition  1/3 – a longer shoulder-touch condition

left a blank survey for customers to complete collected survey and tip

Crusco & Wetzel (1984)
 interested in how touching influences individuals‟ perceptions of others

 description of study
waitress performed normal duties when she gave change to customer, she approached the paying customer from the side, leaned forward, and w/out making eye contact, said in a friendly yet firm tone, “Here‟s your change.”
 1/3 – no touch control condition  1/3 – a brief hand-touch condition  1/3 – a longer shoulder-touch condition

left a blank survey for customers to complete collected survey and tip

IV: nature of physical contact DV: ratings of waitress on Q’aire and amt of tip

A social psychologists wants to assess the optimal level of crowd noise for enhancing the shooting accuracy of professional basketball players. She has individual professional basketball players shoot free throws in a gym as she varies the intensity of crowd noise by playing an audiotape of a crowd at low, medium, and high levels. She randomly assigns the players to the conditions. IV: Conditions:

DV:
Design:

A social psychologists wants to assess the optimal level of crowd noise for enhancing the shooting accuracy of professional basketball players. She has individual professional basketball players shoot free throws in a gym as she varies the intensity of crowd noise by playing an audiotape of a crowd at low, medium, and high levels. She randomly assigns the players to the conditions. IV: Crowd Noise Conditions: low, medium, high

DV: shooting accuracy of free throws
Design: True experiment

Two psychologists are interested in the effects of mood on helping (based on Isen & Levin, 1972). They go to shopping malls and set up observation near phone booths. Their participants are individuals who use the phone booths when the vicinity is otherwise unoccupied. For half of the Ps, the researchers leave a quarter to be found near the booth. For all of the Ps, when the phone call is completed and the person leaves the telephone booth, a confederate walks by the booth, and drops a file folder full of papers. The researchers watch to see if the Ps help pick up the dropped papers. Construct IV and DV? Operational IV and DV?

Two psychologists are interested in the effects of mood on helping (based on Isen & Levin, 1972). They go to shopping malls and set up observation near phone booths. Their participants are individuals who use the phone booths when the vicinity is otherwise unoccupied. For half of the Ps, the researchers leave a quarter to be found near the booth. For all of the Ps, when the phone call is completed and the person leaves the telephone booth, a confederate walks by the booth, and drops a file folder full of papers. The researchers watch to see if the Ps help pick up the dropped papers.

 Constructs
IV: Mood DV: Helping

 Operational
IV: finds a quarter DV: help pick up paper

Researchers are interested in influences on self-esteem. Specifically, researchers want to assess how performing a difficult task under pressure influences college students‟ selfesteem. Ps are given a set of anagrams to solve. Half are randomly assigned to receive very easy anagrams, and half are given difficult ones. Crossed with this, half are randomly assigned to be given 10 minutes to complete the anagrams, and half are given 30 minutes to complete the task. After completing as many of the anagrams as they can, Ps are given a Q‟aire labeled “Thoughts and Feelings Questionnaire” that is really a measure of self-esteem.

Researchers are interested in influences on self-esteem. Specifically, researchers want to assess how performing a difficult task under pressure influences college students‟ selfesteem. Ps are given a set of anagrams to solve. Half are randomly assigned to receive very easy anagrams, and half are given difficult ones. Crossed with this, half are randomly assigned to be given 10 minutes to complete the anagrams, and half are given 30 minutes to complete the task. After completing as many of the anagrams as they can, Ps are given a Q’aire labeled “Thoughts and Feelings Questionnaire” that is really a measure of self-esteem.
 Constructs
IV1: task difficulty IV2: pressure DV: self-esteem

 Operational
IV1: easy vs. hard IV2: 10 vs. 30 minutes DV: score on Q‟aire

Discrete and Continuous Variables
 Discrete Variable - consists of separate, indivisible categories. No values can exist between two neighboring categories
Example?

 Continuous Variable - infinite number of possible values that fall between any two observed values. Divisible into an infinite number of fractional parts
Example?

Real Limits
 Real Limits - the boundaries of intervals for scores that are represented on a continuous number line. Each score has 2 - upper and lower real limit.

Scales of Measurement
    Nominal Scale Ordinal Scale Interval Scale Ratio Scale

Statistical Notation
 Order of mathematical operations  Please excuse my dear aunt sally  Please look over the math review starting on page 703

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