Why is psychology a science?Why is psychology a science?

Scientific Method:Scientific Method: System of gathering data so that System of gathering data so that

bias and error in measurement are bias and error in measurement are reducedreduced

Why is psychology a science?Why is psychology a science?

Scientific Method:Scientific Method:1. Perceive question1. Perceive question2. Form hypothesis 2. Form hypothesis 3. Test hypothesis3. Test hypothesis4. Draw conclusions4. Draw conclusions5. Report results5. Report results

-Replication-Replication

Descriptive methodsDescriptive methods

NaturalisticNaturalistic observation observation Watching behavior in normal environmentWatching behavior in normal environment

Major Advantage:Major Advantage: Realistic dataRealistic data

Descriptive methodsDescriptive methods

NaturalisticNaturalistic observation observation

Disadvantages:Disadvantages: Observer effectObserver effect Observer biasObserver bias Lack generalizeabilityLack generalizeability

Descriptive methodsDescriptive methods

LaboratoryLaboratory observation observation Watching behavior in laboratory environmentWatching behavior in laboratory environment

Advantages:Advantages: ControlControl Specialized equipmentSpecialized equipment

Descriptive methodsDescriptive methods

LaboratoryLaboratory observation observation

Disadvantage:Disadvantage: Artificial situation = artificial behaviorArtificial situation = artificial behavior

Descriptive methodsDescriptive methods

Case studyCase study One individual, great detailOne individual, great detail

Advantage:Advantage:• Tremendous detailTremendous detail

Disadvantages:Disadvantages:• Lack of generealizeabilityLack of generealizeability• Biases in self-reportBiases in self-report

• Phineas GagePhineas Gage

Descriptive methodsDescriptive methods SurveysSurveys

series of questions (e.g., Mate Preferences)series of questions (e.g., Mate Preferences)

Representative sample - Representative sample - randomlyrandomly selected selected sample of from a larger populationsample of from a larger population

Population - entire group of people/animals Population - entire group of people/animals of interestof interest

SamplingSampling

Descriptive methodsDescriptive methods SurveysSurveysAdvantages:Advantages:

Data from large numbers (large N)Data from large numbers (large N) Private informationPrivate information

Disadvantages:Disadvantages: Ensure representative sampleEnsure representative sample Inaccurate data (courtesy bias, memory)Inaccurate data (courtesy bias, memory) Order, wording effectsOrder, wording effects

MeasurementMeasurement

Scientific measurement requires:Scientific measurement requires:

Reliability = consistencyReliability = consistency

Validity = accuracyValidity = accuracy

Measure must be Measure must be reliablereliable: Coke : Coke vs. Pepsivs. Pepsi

Reliability:Reliability: Interrater reliabilityInterrater reliability-Do -Do observersobservers agree? agree?

Test-retest reliabilityTest-retest reliability--Are measures consistent Are measures consistent over over timetime??

BUT people might self report liking Coke very consistently simplybecause they reliably like the advertising.

Advertising preferencesAdvertising preferences

Measure must be Measure must be validvalid: : Coke vs. PepsiCoke vs. Pepsi

Internal validityInternal validity-Are-Are effects due to conditionseffects due to conditions manipulated?manipulated?

e.g., preference may comefrom product advertising orfrom product taste (e.g., initial sweetness)

Measure must be Measure must be validvalid: : Coke vs. PepsiCoke vs. Pepsi

Internal validityInternal validity-Are-Are effects due to conditionseffects due to conditions manipulated?manipulated?

... A blind taste-test would be a... A blind taste-test would be abetter measure…it wouldbetter measure…it wouldeliminate brand loyalty as aeliminate brand loyalty as avariable ( = higher internal validity)variable ( = higher internal validity)

Types of research designs: Types of research designs: relationshipsrelationships between variables between variables

CorrelationalCorrelational

ExperimentalExperimental

Quasi-experimentalQuasi-experimental

Types of research designs: Types of research designs: relationshipsrelationships between variables between variables

Correlational:Correlational: Association between variablesAssociation between variables No manipulationNo manipulation Correlation coefficient: r (range: -1.0-+1.0)Correlation coefficient: r (range: -1.0-+1.0) Correlations does not equal causation!Correlations does not equal causation!

Correlational researchCorrelational research

CorrelationCorrelation relationship between two variablesrelationship between two variables

VariableVariable• Anything that can change or varyAnything that can change or vary

Types of research designs: Types of research designs: relationshipsrelationships between variables between variables

Experimental:Experimental: CausalCausal relationship between variables relationship between variables Experimental manipulationExperimental manipulation

Types of research designs: Types of research designs: relationshipsrelationships between variables between variables

Quasi-experimental:Quasi-experimental: No manipulation possibleNo manipulation possible

Correlational research Correlational research

Correlational researchCorrelational research

CorrelationCorrelation Measures of two variablesMeasures of two variables Mathematical formulaMathematical formula

Correlation coefficient (r)Correlation coefficient (r), , representsrepresents1. direction of relationship (+/-)1. direction of relationship (+/-)2. strength of relationship 2. strength of relationship

Correlational researchCorrelational research

Correlation coefficient (r):Correlation coefficient (r):––1.00 to +1.001.00 to +1.00

Closer to 1.00 or -1.00, the stronger the Closer to 1.00 or -1.00, the stronger the relationshiprelationship

No correlation = 0.0No correlation = 0.0 Perfect correlation = -1.00 OR +1.00Perfect correlation = -1.00 OR +1.00

Correlational researchCorrelational research Positive correlation – Positive correlation – samesame direction direction

One increases, the other increases; one One increases, the other increases; one decreases, the other decreasesdecreases, the other decreases

Negative correlation – opposite directionNegative correlation – opposite direction One increases, other decreases.One increases, other decreases.

CORRELATION DOES CORRELATION DOES NOTNOT EQUAL EQUAL CAUSATION!!!CAUSATION!!!

Experimental researchExperimental research

manipulation of a variable manipulation of a variable

to see if changes in behavior resultto see if changes in behavior result

determination of cause-and-effect determination of cause-and-effect relationshipsrelationships

Experimental researchExperimental research

Operational definitionOperational definition Definition variable of interest Definition variable of interest Allows precise, direct measurementAllows precise, direct measurementExample: Aggression Example: Aggression

Variables in experimental designVariables in experimental design

Independent variableIndependent variable-what is manipulated-what is manipulated e.g., Prozac dosagee.g., Prozac dosage e.g., Violent TVe.g., Violent TV

Dependent variableDependent variable-what is measured, the -what is measured, the outcomeoutcome e.g., Depressione.g., Depression e.g., aggressive playe.g., aggressive play

ParticipantsParticipants in experimental design in experimental design

Experimental groupExperimental group: group whose environment : group whose environment or experience has changedor experience has changed e.g., Prozace.g., Prozac e.g., TVe.g., TV

Control groupControl group: group treated as much like : group treated as much like experimental group as possibleexperimental group as possible Does NOT participate in experimental manipulationDoes NOT participate in experimental manipulation

• e.g., No Prozac, sugar pille.g., No Prozac, sugar pill• No TVNo TV

Random assignmentRandom assignment Assignment to experimental or control groups Assignment to experimental or control groups

randomlyrandomly Participants have an equal chance of being in Participants have an equal chance of being in

either groupeither group

Controls for confounding variablesControls for confounding variables

Experimental designExperimental design

Placebo effectPlacebo effect expectations of the participants influence expectations of the participants influence

behavior (e.g., Viagra vs. sugar pill)behavior (e.g., Viagra vs. sugar pill)

Single-blind studySingle-blind study Participants do NOT know if they are in the Participants do NOT know if they are in the

experimental or the control group (reduces experimental or the control group (reduces placebo effect)placebo effect)

Experimental designExperimental design

Experimenter effectExperimenter effect Experimenter’s expectations influence resultsExperimenter’s expectations influence results

Double-blind studyDouble-blind study NeitherNeither the experimenter nor the participants the experimenter nor the participants

know group assignment (reduces placebo and know group assignment (reduces placebo and experimenter effect)experimenter effect)

Correlational designCorrelational design

Correlational designCorrelational design

ResultsResults::

Correlational designCorrelational design

Conclusions:Conclusions: NONO causal relationship can be inferred causal relationship can be inferred

Experimental designExperimental design

QuestionQuestion: Does close physical contact : Does close physical contact promote secure infant-mother attachment?promote secure infant-mother attachment?

MethodMethod: Women : Women randomlyrandomly assigned to assigned to use “Snuglis” (experimental) or standard use “Snuglis” (experimental) or standard infant seats (control) to carry their infantsinfant seats (control) to carry their infants

Experimental designExperimental design ResultsResults: Carrier effect on attachment: Carrier effect on attachment

SnuglisSnuglis: more responsive moms, infants more : more responsive moms, infants more likely to develop secure attachmentlikely to develop secure attachment

Standard carrierStandard carrier: less responsive moms, : less responsive moms, infants less likely to develop secure attachmentinfants less likely to develop secure attachment

ConclusionConclusion: : causalcausal relationship between relationship between type of carrier and attachmenttype of carrier and attachment