Research MethodsPsych 402

LECTURE 3

VHS – Teaching Modules Experimental Design (Experimental design, variables)

Assignment 1: LIBRARY SEARCHAssignment 1: LIBRARY SEARCHDue WedDue Wed

1. Number EEG papers on autism (autism, asperger, autistic)2. Number of sleep deprivation papers on high school kids3. Number of subjects in the one study on sleep deprivation, naps, and

caffeine in high school kids4. Number of papers published by Carl Sagan in English5. Number of sleep papers published since January 1, 19806. Number of co-authored papers by DA Kaiser & MB Sterman7. Maximum score on Autism Spectrum Quotient Test (AQ Test) 8. Maximum female score on the AQ test = CHECK MEDLINE

ABSTRACTS9. Size in grams of Immanuel Kant’s brain 10. Publication year of the one book in Wallace library on a feral/neglected

child who was discovered in the 20th century

Use Medline for questions 1-5PsycInfo for question 6any source for remainder

• QUANTIFICATION OF BEHAVIOR

• Descriptive Statistics• Characteristics of your sample

– Central tendency– Dispersion

• Inferential Statistics – How likely your sample reflects the population

MeanMean

MEAN is arithmetic average

• 1• 1• 6• 5• 2• Mean = total divided

number of items, 15/5 = 3

• PROBLEMS WITH MEANS

– EXAMPLE– Kirkwell WA mean per capita

income is $1,200K– I survey the gas stations, movie

theaters, country clubs, and rarely find anyone at or near this value

Means are sensitive to extremesMeans are sensitive to extremes

Median is the middle valueMedian is the middle value• Arrange in order,

middle value is median

• 1• 1• 2 • 5• 6• Median = 2

• When even number of items– Arrange in order, average of

middle two values

• 1• 1• 2 • 5 • 6• 7• Median = (2+5)/2 = 3.5

Median’s advantage: Median’s advantage: Not sensitive to extremesNot sensitive to extremes

• 1• 1• 2 • 5• 6• Median = 2

• 1• 1• 2 • 5• 6 billion• Median = 2

• -150• 1• 2 • 5• 6• Median = 2

Example: Example: Kirkwell WA median per capita income is $70KKirkwell WA median per capita income is $70K

Median disadvantage: it’s nonlinear!Median disadvantage: it’s nonlinear!(e.g., affected by grouping, other influences)(e.g., affected by grouping, other influences)

• 1• 1• 4

• Median =1

• 4• 4• 16

• Median =4

Median for all numbers = (1+4)/2 = 2.5

• 1• 1• 4• 4• 4• 16

• Median =4

ModeMode

• Most frequent value

• 1 • 1 • 2• 5• 6• Mode = 1

• EXAMPLE• Kirkwell WA modal

per capita income is $13K – (as it is in all cities)

Mode is also nonlinear! Mode is also nonlinear!

• 1• 1• 4

• Mode =1

• 4• 4• 16

• Mode =4

Mode for all numbers = (1+4)/2 = 2.5

• 1• 1• 4• 4• 4• 16

• Mode =4

How well central tendency describes data? How well central tendency describes data? - Needs index of dispersion- Needs index of dispersion

• 1• 2• 3• 4• 5• 6• 7• 8• 9• Mean = 5

• 4• 4• 5• 5• 5• 5• 5• 6• 6• Mean = 5

DispersionDispersion: Range: Range

• 1• 2• 3• 4• 5• 6• 7• 8• 9• Mean = 5, Range = 8

• 4• 4• 5• 5• 5• 5• 5• 6• 6• Mean = 5, Range = 2

DispersionDispersion: Standard Deviation: Standard Deviation(Std Dev takes into account each sample’s distance from mean)(Std Dev takes into account each sample’s distance from mean)

• 4• 4• 4• 4• 5• 6• 6• 6• 6

• Mean = 5, Range = 2• St Dev = 0.88

• 4• 5 • 5• 5• 5• 5 • 5 • 5• 6

• Mean = 5, Range = 2• Std Dev = 0.44

Measurement ScalesNominal or

categoricalOrdinal Interval Ratio

Same scale value are the same on some attribute.

No 'numeric' meaning in the way that you usually think about numbers.

Higher scale value indicates more of some attribute.

Intervals between adjacent values vary

Intervals between adjacent values are equal on attribute

E.g., difference between 8 and 9 is same as difference between 76 and 77.

Meaningful zero point

Ratios are equivalent, e.g., ratio of 2 to 1 is the same as the ratio of 8 to 4.

Nominal Ordinal Interval Ratio

Gender.

Ethnicity.

Marital Status. 

SES

USDA beef ratings (good, choice, prime) Hospitalization

Rank order of anything.

Degrees F.

Letter Grades

IQ, SAT 

Degrees K.

Annual income in dollars.

Time or distance

Role of FiguresRole of Figuresin Scientific Papersin Scientific Papers

• Argument made in pictures, not words!

Figures used for:Figures used for:

• DATA

• METHOD

• THEORY

• Compress information

Three mountain test for Three mountain test for egocentrismegocentrism

Hierarchical memory storage Hierarchical memory storage

Lying with statisticsLying with statistics

Assumed linearityAssumed linearity

Lie Factor =Lie Factor =

• Size of effect shown in graphic/size of effect in data

Quantify Brain Behavior (EEG)Quantify Brain Behavior (EEG)

Quantify EyetrackingQuantify Eyetracking

Ages, wealth, length of absenceAges, wealth, length of absence

RESEARCH VARIABLESIndependent variable (IV): Variable manipulated by

researcher

Dependent variable (DV): Variable measured by researcher, expected to change as a result of researcher’s manipulation (“depends on IV”)

Control variables (CV): Factors kept constant (e.g., confederate, room).

Random variables (RV): Factors allowed to vary randomly.

(e.g. time of day effects, fatigue, motivation)

Confounding variable: Variable’s levels covary with IV’s and may be responsible for changes

• My hypothesis: – When people are angry, they drive more

aggressively• IV: Anger

– Level 1. Drop 5 lb weight on subject’s foot 3 or 4 times– Level 2. Drop feather on subject’s foot 3 or 4 times

• DV: Aggressive driving– How can I quantify aggressive driving?

• Are aggressive people aggressive drivers?

OPERATIONAL DEFINITION

Specify operations required to manipulate or measure concept.

e.g. Anxiety is not vaguely described but explicitly measured by objectively through subjective report scales, behavior checkboxes, etc