Lecture 4: Web Chapter 1 Statistics for Psychology David Wallace Croft 2005 May 25 Wed Copyright 2005 David Wallace Croft This work is licensed under the Creative Commons Attribution License 2.0. Creative Commons Attribution License 2.0

Quiz Please mute your mobile phones Write your name on a blank piece of paper Quiz will begin at 09:00 When done, turn your paper over At 09:02, I will say, “Pens down” Writing after “Pens down” is cheating Pass your quizzes to your left

Outline See Saw Demo Scientific Method Web Chapter 1 Exam Review Next Class

Hypothesis vs. Theory A Hypothesis is a theory A Theory is a thoroughly tested Hypothesis –Atomic Theory –Cell Theory –Germ Theory

See Saw Demo Torque = moment of force Moment = product of distance from reference point and some other quantity Deviation = distance from mean = distance from balance point

Scientific MethodScientific Method O b s e r v e d a t a F o r m h y p o t h e s i s T e s t h y p o t h e s i s w i t h e x p e r i m e n t R e v i s e a n d r e t e s t Scientific Method Observe nature Form hypothesis Test hypothesis using experiment Revise hypothesis and retest

Scientific MethodScientific Method O b s e r v e d a t a F o r m h y p o t h e s i s T e s t h y p o t h e s i s w i t h e x p e r i m e n t R e v i s e a n d r e t e s t Scientific Method 2 Observe Hypothesize Predict Verify Evaluate Publish Reproduce -- Wikipedia, ~

Web Chapter 1 Overview of the Logic and Language of Psychology Research Web chapter for Aron and Aron, “Statistics for Psychology”, 3 rd Ed., 2003.

True Experiment Hypothesis: X causes Y Systematically vary X Everything else the same

Groups Experimental Group Control Group No control group

Participants Subjects

Variables Independent variable Dependent variable Manipulate independent variable Dependent variable should follow If not, no cause-effect relationship in that direction

Population vs. Sample Population Sample N – 1

Ideal Research Design Participants in both groups identical Identical situations except manipulated variable Sample represents population Measurement is accurate and appropriate

Participants Identical Random assignment No systematic difference Examples

Situations Identical Different room Different lighting Different time of day Different person giving instructions Avoid systematic difference other than manipulated variable

Double-Blind Experiment Placebo and Hawthorne Effect Experimenter bias Double-blind procedure Free weights Marital counselling Communication disorders

Representativeness of the Sample Sample vs. Population Generalizability or external validity Flukey sample Registered voters vs. likely voters College students Recruitment Random sampling

Measurement Accurate and Appropriate Inaccurate: grading or transcription error Inappropriate: bad question on exam

Significance of Statistics Back surgery Cough suppressant Hormone replacement therapy -- Steven Bratman, “The Double-Blind Gaze: How the Double-Blind Experimental Protocol Changed Science”, Skeptic, Volume 11, Number 3, 2005.

Exam Review Exam review next class

Next Class Friday Read Chapter 3 before class Quiz at start of class Monday no class Memorial Day

Questions Questions for Class? Post to list unless personal –ttp://groups.com/group/utdstatisticsttp://groups.com/group/utdstatistics