Experimental Studies

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Educational Research:

Experimental Studies Experimental Studies

Educational Research

S.Shafiee

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Research...

 The systematic application of a family of methods employed to provide trustworthy information about problems

…an ongoing process based on many accumulated understandings and

explanations that, when taken together lead to generalizations about problems and the development of theories

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 experimental researchexperimental research

…the researcher selects participants and divides them into two or more

groups having similar characteristics and, then, applies the treatment(s) to the groups and measures the effects upon the groups

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Conducting an experimental study…

1. select the problem

2. select participants and instrument 3. selection and execution of a

research plan

4. data analysis and formulation of conclusions

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Characteristics of experimental Characteristics of experimental research

research

 Control

 Manipulation

 Observation

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Confounding Confounding…

…the fact that the effects of the

independent variable may intertwine with extraneous variables, such that it is difficult to determine the unique effects of each variable

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Types of experimental comparison…

1. comparison of two different approaches (A A versus BB)

2. comparison of an existing approach to a new approach (AA and ~~ AA)

Placebo treatment

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where:

A – experimental (“treatment”) group B – control (“no treatment,”

“nonmanipulated”) group

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The concept of validity…

…the experiment tests the variable(s) that it purports to test

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Internal validity…

The extent to which the changes

observed in a dependent variable are caused by the independent variable in a particular experimental situation

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Threats to internal validity…

1. history

2. maturation 3. testing

4. instrumentation

6. differential selection of participants 7. Mortality and attrition

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 historyhistory

…the occurrence of events that are not part of the experimental treatment

but that occur during the study and affect the dependent variable

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 maturationmaturation

…the physical, intellectual, and emotional changes that occur

naturally in a study’s participants over a period of time

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 testingtesting

…refers to improved scores on a

posttest as a result of having taken a pretest

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 mortalitymortality

…the case in which participants drop out of a study which changes the characteristics of the groups and may significantly affect the study’s results

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 selectionselection--maturation interactionmaturation interaction

…if already-formed groups are used in a study, one group may profit more (or less) from a treatment or have an initial advantage because of

maturation, history, or testing factors

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external validity…

Generalizability or representativeness of the findings

The extent to which the results of an experiment can be generalized to different subjects, settings and situations.

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There is a trade-off between external and internal validity.

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 singlesingle--variable designsvariable designs

…involve one manipulated independent variable

pre

pre--experimentalexperimental quasi

quasi--experimentalexperimental true experimental true experimental

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Pre-Experimental Designs:

No Control Group and/or Randomization

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 types of pretypes of pre--experimental designsexperimental designs one

one--shot case studyshot case study X T

…a single group exposed to a treatment ( X ) and then

posttested ( T)

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one

one--group pretestgroup pretest--posttest designposttest design T1 X T2

…a single group is pretested ( T1 ), exposed to a treatment ( X ) and, then, is posttested ( T2 )

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Static/intact group comparison Static/intact group comparison

G1 X T G2 O T

…involves at least two groups ( G1 and G2 ), one receiving a new, or

experimental treatment ( X₁ ) and another receiving a traditional, or

control treatment ( O ) and, then, are posttested ( T )

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 types of quasitypes of quasi--experimental designsexperimental designs equivalent time sample

equivalent time sample O X O

…random assignment of intact groups that are pretested ( O ), exposed to a treatment ( X ) and then posttested ( O )

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time

time--series designseries design

T1 T2 T3 X T4 T5 T6

…a single group is pretested (T1 T2 T3 )repeatedly until pretest scores are stable, exposed to a treatment ( X ) and, then, is repeatedly

posttested (T4 T5 T6 )

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Equivalent time design Equivalent time design

T1 X T2/T3 O T4/T5 X T6/T7 O T8

After and before the treatment there is a test. After the second pretest (T3) a placebo is introduced followed by a posttest. This procedure is repeated and the scores obtained after applying treatment is compared with scores

after the placebo.

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Mini

Mini--Quiz… Quiz…

 True and false…

…experimental researcher is the only type of research that can test

hypotheses to establish cause-and- effect relationships

True

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…the manipulation of the independent variable is the one characteristic that differentiates correlational research from other types of research

False

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…an experimental study is guided by at least one hypothesis that states an expected causal relationship

between two variables

True

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…the “experiment” in an experimental study is conducted to conform or

disconfirm the research problem

False

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…experimental research has both

random selection and assignment whereas causal-comparative

research has random selection not assignment

True

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…it is correct to state that a control

group always receives no treatment in experimental studies

False

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…in an experimental study, the

researcher makes every effort to

ensure that the two groups start as equivalently as possible on all

variables except the independent variable

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True

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…in an experimental study, the researcher collects data on the independent variable from the

groups to determine whether there is a significant difference between their performances

False

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…in an experimental study, the

researcher endeavors to make the

groups as similar as possible so that the only major difference between

them is the treatment variable(s) manipulated by the researcher

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True

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…even though experimental research is the only type of research that can truly establish cause-effect

relationships, it is not universally appropriate for all research

problems or studies

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True

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…an experiment is valid if results

obtained are due only to the control variable and if they are generalizable to individuals or contexts beyond the experimental setting

False

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…internal validity focuses upon

threats or rival explanations that influence the outcomes of an

experimental study but are not part of the independent variable

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True

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…if a study’s results cannot be

replicated in other settings by other researchers, then the study has low external reliability

False

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…to conduct a valid experiment, all the researcher has to do is to maximize internal and external validity

False

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…true experimental designs control for all sources of internal and external

validity

False

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…the more narrowed and controlled a research situation is, the less

realistic and generalizable it becomes

True

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…a study that is not internally valid is worthless

True

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…the longer a study lasts, the more likely it is that history will be a

threat to the study’s internal validity

True

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…the way a researcher controls for selection-maturation interaction is to select a design that controls for potential problems or to make

every effort to determine if

selection-maturation interaction is operating in the study

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True

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…even if intact groups are randomly selected, the possibility exists that the experimental group is in some important way different from the

control group and/or from the larger population

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True

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…it is possible to know what a

researcher means by the terms

assigned to variables without clear operationalized descriptions

False

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…good designs control for many

sources of invalidity, poor designs control few

True

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…a researcher should decide which

research design is most appropriate not only by the controls provided but also by the nature of the study and

the setting in which it is to be conducted

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True

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…in a static-group comparison design, each group serves as a control or

comparison group for the other group(s)

True

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…in a true experimental designs, participants should be randomly selected or randomly assigned

False

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…the more dissimilar the intact groups in a study are, the stronger the study is

False

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 Fill in the blank…

…the researcher decides what treatment(s) will constitute the independent variable and which group will get which treatment

manipulation

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…the researcher’s efforts to remove the influence of any extraneous

variable that might affect scores on the dependent variable

control

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…the researcher’s concern with threats or factors other than the

independent variable that affect the dependent variable

internal validity

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…the researcher’s concern with the extent to which the study results can be generalized to groups and settings beyond those of the

experiment

external validity

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…a threat to internal validity that may be overcome by testing for initial

equivalence between groups

differential selection of participants

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…an external variable that effects the independent variable and

intertwines with other extraneous variables such that it is difficult to determine the unique effects of each

confounding variable

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…a study to compare the achievement of two groups: one group taught in an anxiety-producing environment and one group taught in an anxiety- reducing environment

experimental

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…the nonmanipulated variable in a factorial design

control variable