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Experimental Control

RS: Ch 9 Experimental control

What is the most rigorous form of scientific investigation, and the best process for testing hypotheses THE EXPERIMENT
The purpose of the Experiment: The purpose is to support a cause-and-effect relationship
What is the Experiment: Researcher systematically introduces changes into natural phenomenaObserves consequences of those changesMust have sufficient control over ex situation to be a true exThose variables that are not able to be controlled are considered limitations
One drawback – to the Experiment: if too much control can’t apply to the real world
Extraneous variables Are considered confounding variablesAny factor that is not directly related to the purpose of the studyNot related but affects the DVCan be extrinsic factors or intrinsic factors
If an Extraneous Variable is not controlled it can exert a ________ can exert a confounding influence on the IV
Experiments are designed to control for________ designed to control for these confounding influences
Extrinsic Factors: factors that emerge from the environment and the experimental situation
Intrinsic Factors: represent personal characteristics of the subjects of the study.
Confounding is the contaminating effect of extraneous variable on the interpretation of the relationship between independent and dependent variable.
ESSENTIAL CHARACTERISTICS OF A true EXPERIMENT The independent variable must be manipulated by the researcherThe participants must be randomly assigned to groupsA control group must be incorporated within the design
MANIPULATION OF VARIABLES Researcher deliberately imposes an experimental condition (IV) on at least one group of participantsParticipants are assigned to different levels of the IV
The the Researcher does what to the active variable : MANIPULATES
The the Researcher does what to the attribute variable: does NOT manipuate
Active variable: is an independen variable with levels that can be Manipulates and assigned by the researcher
Attribute variable: is an independent variable with levels that cannot be manipulated or asigned by the researcher, but hat represent the subject characteristics (such as age or sex)
RANDOM ASSIGNMENT Each participant has an equal chance of being assigned to any groupAssignments are independent of personal judgment or biasGroups are then theoretically considered “equivalent”
Def of Random Assignment is the assignment of subjects to groups using probability methods, where every subject has an equal chance of being assigned to each group.
Equivalence: means any differenes between groups are due to chance alone, this way inter-participant differences should balance out
Randomization is an issue of probability!Done by use of random numbers table or computer
Use of control group is the most effective way for ruling out extraneous effects
The control group usually receives no treatment or the “standard” treatment
The treatment group receives the manipulation
Double-blinded study: is an experiment in which both the investigator and the subject are kept ignorant of group assignment
Single-blinded study: an experiment in which either the investigator or the subject is kept ignoratnt of group assignment, not both Ronda- only experimenter is blind
CONTROLLING INTER-PARTICIPANT DIFFERENCES Selecting homogeneous participantsBlockingMatchingSubjects as own controlAnalysis of Covariance (ANCOVA)
Homogeneous participants Selected based on homogeneous characteristicsExample:Gender or age makes a differences
blocking Builds the attribute variables into the experimental design as an IVExample:If age makes a difference have different age groupsRandomly assign participants within the group – randomized block design
Block is a level of an attribute variable in which subjects are homogeneous on a particular characteristic
Blinding are techniques to reduce experimental bias by keeping the subjects and/or investiagators ignorant of group assignmetns and research hypotheses
Confounding Variable: a variable taht is more likely to be present in one group of subjects than another, and that is related to the outcome of interest, thereby potentially "confounding" interpretation of the outcome.
what is matching, give some examples Participants “matched” based on specific characteristic(s)Example:AgeSexDisease
participants as own control All participants receive all levels of the IVRepeated measures design
ANALYSIS OF COVARIANCE A statistical analysis that eliminates influences of extraneous factorsThese extraneous factors become the covariatesThe process makes covariates artificially equivalent across groups
Analysis of covariance ( ANCOVA) uses a statistical technique to equate groups on extraneous variables. ANCOVA is based on concepts of analysis of variance and regression.
Created by: NicoleB