Causation and Causation and Experimental DesignsExperimental Designs

Causal ExplanationCausal Explanation

Ultimately, research efforts focus on our Ultimately, research efforts focus on our ability to draw a cause and effect ability to draw a cause and effect relationship between variables in our relationship between variables in our study.study.

Simply put, if we can find the cause then Simply put, if we can find the cause then we “ought” to be able to do something we “ought” to be able to do something about it. Makes sense, right?about it. Makes sense, right?

How do we prove it?How do we prove it?

How do we prove that something is How do we prove that something is causingcausing something else to occur? something else to occur?

Variables may be correlated and causally Variables may be correlated and causally linked. Suggesting that they fluctuate linked. Suggesting that they fluctuate together, but may in fact be caused by a together, but may in fact be caused by a 33rdrd variable. Or a combination of other variable. Or a combination of other factors.factors.

Criteria for CausalityCriteria for Causality

There are three criteria necessary for There are three criteria necessary for determining causality:determining causality:

1. Empirical Association1. Empirical Association2. Time Order2. Time Order3. Nonspuriousness3. Nonspuriousness

In addition, there are two criteria for In addition, there are two criteria for specifying causality:specifying causality:

1. Mechanism1. Mechanism2. Context2. Context

Empirical AssociationEmpirical Association

The empirical association simply refers to The empirical association simply refers to the connection between the variables; or the connection between the variables; or the link between the cause and effect.the link between the cause and effect.

We seek similar fluctuations in groups or We seek similar fluctuations in groups or individuals that suggest a pattern of individuals that suggest a pattern of behaviors or observations.behaviors or observations.

Time OrderTime Order

This may seem ridiculous to address, but This may seem ridiculous to address, but in order to determine cause and effect we in order to determine cause and effect we need to establish that the cause occurred need to establish that the cause occurred prior to the effect.prior to the effect.

Seems simple enough.Seems simple enough.

How often do we actually do it?How often do we actually do it?

NonspuriousnessNonspuriousness

Nonspuriousness refers to the necessity of Nonspuriousness refers to the necessity of insuring that the measured relationship is insuring that the measured relationship is not in fact the product of a variable going not in fact the product of a variable going unmeasured.unmeasured.

““Correlation does not prove causation”.Correlation does not prove causation”.

How about the adage that drugs cause How about the adage that drugs cause crime?crime?

MechanismMechanism

How is the cause impacting the effect? In How is the cause impacting the effect? In other words, it’s not simply enough that other words, it’s not simply enough that the association is observed, but we must the association is observed, but we must be able to identify the delivery of the cause be able to identify the delivery of the cause upon the effect.upon the effect.

How does poverty cause crime?How does poverty cause crime?Lack of opportunities, class struggle, Lack of opportunities, class struggle,

disenfranchisement, etc.disenfranchisement, etc.

ContextContext

In any type of social science research we In any type of social science research we recognize that we are unable to separate recognize that we are unable to separate the research from the larger context of the research from the larger context of factors affecting individuals or groups.factors affecting individuals or groups.

We need to address strengths or We need to address strengths or weaknesses of examining the individual or weaknesses of examining the individual or group within the current context.group within the current context.

Research DesignResearch Design

The construction of a research design The construction of a research design seeks to address some, if not all, of these seeks to address some, if not all, of these concerns.concerns.

True ExperimentsTrue ExperimentsQuasi ExperimentsQuasi Experiments

Is all research experimental?Is all research experimental?

True ExperimentsTrue Experiments

True experiments are experimental True experiments are experimental designs that meet three criteria:designs that meet three criteria:

1. Two comparison groups1. Two comparison groupsa. 1 experimentala. 1 experimentalb. 1 control/comparison groupb. 1 control/comparison group

2. Random Assignment2. Random Assignment3. Assessment of Change3. Assessment of Change

GroupsGroups

An experimental group is the groups of An experimental group is the groups of subjects within the study that receive subjects within the study that receive treatment or an experimental treatment or an experimental manipulation.manipulation.

A control group receives no treatment.A control group receives no treatment.

A comparison group receives an A comparison group receives an alternative treatment.alternative treatment.

Random AssignmentRandom Assignment

Random assignment attempts to insure Random assignment attempts to insure that the only difference between the that the only difference between the groups is the treatment/experimental groups is the treatment/experimental manipulation.manipulation.

This is different than random sampling.This is different than random sampling.

Random sampling attempts to insure Random sampling attempts to insure generalizability, this attempts to insure generalizability, this attempts to insure internal validity.internal validity.

Assessment of ChangeAssessment of Change

Assessment of change simply refers to a Assessment of change simply refers to a measurement of the group/individual measurement of the group/individual following the treatment/experimental following the treatment/experimental manipulation.manipulation.

We often refer to this as a post-test.We often refer to this as a post-test.

Quasi-Experimental DesignQuasi-Experimental Design

Much like our discussion of probability Much like our discussion of probability versus nonprobability sampling, we versus nonprobability sampling, we recognize that sometimes we can’t always recognize that sometimes we can’t always use the preferred method.use the preferred method.

The use of a quasi-experimental design is The use of a quasi-experimental design is similar to this. We recognize that it similar to this. We recognize that it contains more flaws than a true contains more flaws than a true experiment, but it may be our best/only experiment, but it may be our best/only choice.choice.

Goal of a quasi-experimentGoal of a quasi-experiment

In short, a quasi-experiment fails to have In short, a quasi-experiment fails to have random assignment to a control group and random assignment to a control group and experimental group.experimental group.

The implementation of a quasi-experimental The implementation of a quasi-experimental design is meant to maximize the internal design is meant to maximize the internal validity of the study. validity of the study.

Recognizing that it falls short of a true Recognizing that it falls short of a true experiment.experiment.

Language of DesignLanguage of Design

O = ObservationO = ObservationOO11 = Observation 1 = Observation 1

OO22 = Observation 2, etc. = Observation 2, etc.

X = Experimental TreatmentX = Experimental Treatment

R = Random AssignmentR = Random Assignment

Internal Validity ConcernsInternal Validity Concerns

Internal ValidityInternal ValidityHistoryHistory

MaturationMaturation

TestingTesting

InstrumentationInstrumentation

Selection BiasSelection Bias

Types of True-ExperimentsTypes of True-Experiments

Pretest-Posttest Control Group DesignPretest-Posttest Control Group Design

Solomon Four-Group DesignSolomon Four-Group Design

Posttest-Only Control Group DesignPosttest-Only Control Group Design

Pretest-Posttest Control Group DesignPretest-Posttest Control Group Design

RR OO11 XX OO22

RR OO11 OO22

The pretest-posttest control group design The pretest-posttest control group design is recognized as one of the strongest is recognized as one of the strongest experimental designs.experimental designs.Random assignment increases the Random assignment increases the probability of similarities between control probability of similarities between control and experimental groups.and experimental groups.

Solomon Four-Group DesignSolomon Four-Group Design

RR OO11 XX OO22

RR OO11 OO22

RR XX OO22

RR OO22

Arguably the strongest and most Arguably the strongest and most sophisticated design. Insuring that sophisticated design. Insuring that treatment and testing are causing an impact.treatment and testing are causing an impact.

Posttest-Only Control Group DesignPosttest-Only Control Group Design

RR XX OO11

RR OO11

While less sophisticated than the previous While less sophisticated than the previous two, the posttest-only control group design two, the posttest-only control group design is strong due to the nature of the random is strong due to the nature of the random assignment and the control group having assignment and the control group having little or no interaction with the testing.little or no interaction with the testing.

Types of Quasi-ExperimentsTypes of Quasi-Experiments

Time-SeriesTime-Series

Nonequivalent Control GroupNonequivalent Control Group

Time-SeriesTime-Series

aka Longitudinalaka Longitudinalaka Life-courseaka Life-course

0011 0 022 0 033 0 044 X 0 X 055 0 066 0 077 0 088

Multiple observations prior and following Multiple observations prior and following the intervention allow us to examine the intervention allow us to examine impacts of the intervention.impacts of the intervention.

Nonequivalent Control GroupNonequivalent Control Group

O O X X OOO O OO

The nonequivalent control group design The nonequivalent control group design should not be confused with the pretest-should not be confused with the pretest-posttest control group design (a true posttest control group design (a true experiment).experiment).Here we have no assumption of reliability Here we have no assumption of reliability between the two groups prior to the between the two groups prior to the intervention.intervention.

Causation and Causation and Experimental DesignsExperimental Designs