1. © LOUIS COHEN, LAWRENCE MANION & KEITH MORRISON
EXPERIMENTS
© LOUIS COHEN, LAWRENCE MANION & KEITH MORRISON

2. STRUCTURE OF THE CHAPTER
Designs in educational experimentation
True experimental designs
A quasi-experimental design: the non-equivalent control group design
Single-case research: ABAB design
Procedures in conducting experimental research
Threats to internal and external validity in experiments
The timing of the pretest and the post-test
Examples from educational research
The design experiment
Internet-based experiments

3. CAUSALITY
Experiments are held up to be able to identify causality through control and manipulation of variables.
Examine the effect of an independent variable on a dependent variable.
Identifying the effects of causes by implementing interventions in a controlled environment.
Held up to be able to offer explanations for outcomes.

4. INDEPENDENT AND
DEPENDENT VARIABLES

5. RANDOMIZATION
Random sampling and random allocation to either a control or experimental group.
Randomization allows for the many additional uncontrolled and, hence, unmeasured, variables that may be part of the make-up of the groups in question.
Randomization operates the ceteris paribus condition (all other things being equal), assuming that the distribution of extraneous variables is more or less even and perhaps of little significance.
Randomization strives to address Holland’s (1986) ‘fundamental problem of causal inference’, which is that a person may not be in both a control group and an experimental group simultaneously.

6. CONCERNS IN EXPERIMENTS
It may not be possible or desirable to isolate and control variables under laboratory conditions.
The ‘real world’ is not the antiseptic, artificial world of the laboratory.
Cannot assume that a single cause produces a single effect.
The setting affects the outcomes.

7. BLIND AND DOUBLE-BLIND EXPERIMENTS
Blind experiment: participants do not know to which group they are assigned.
Double blind experiment: neither the researcher nor the participants know to which group the participants are assigned.

8. KINDS OF EXPERIMENT
Laboratory experiments (controlled, artificial conditions):
Pretest-post-test control and experimental group
Two control groups and one experimental group pretest-post-test
Post-test control and experimental group
Post-test two experimental groups
Pretest-post-test two treatment
Matched pairs;
Factorial design;
Parametric design;
Repeated measures design;
Field experiments (controlled conditions in the ‘real world’):
one-group pretest-post-test;
non-equivalent control group design;
time series
Natural experiments (no control over real world conditions)

9. FEATURES OF A TRUE EXPERIMENT
Random allocation of the sample to control or experimental groups;
Identification and isolation of key variables;
Control of the key variables;
Exclusion of any other variables;
Special treatment (the intervention) given to the experimental group (i.e. manipulating the independent variable) whilst holding every other variable constant for the two groups;
Ensuring that the two groups are entirely separate throughout the experiment (non-contamination);
Final measurement of outcomes to compare the control and experimental groups and to look at differences from the pre-test results (the post-test);
Comparison of one group with another.

10. Stages in an experiment Randomly assign subjects
to two matched groups:
control and experimental group
Conduct pre-test
Isolate and control variables,
exclude other variables
Administer intervention to
experimental group
Conduct post-test and compare
control and experimental groups

11. ‘TRUE’ EXPERIMENTAL DESIGN
Intervention
EXPERIMENT
PLUS
Matched on
Pre-test
Post-test
Isolate,
control and
manipulate
variables
Random group
assignation
CONTROL
CONTROL

12. MEASURING EFFECTS Average causal effect (A): where:
= (E1E2)  (C1C2)
where:
E1 = post-test for experimental group;
E2 = pretest for experimental group;
C1 = post-test for control group;
C2 = pretest for control group.

13. CAMPBELL’S AND STANLEY’S NOTATION
X represents the exposure of a group to an experimental variable or event, the effects of which are to be measured.
O refers to the process of observation or measurement.
Xs and Os in a given row are applied to the same persons.
Left to right order indicates temporal sequence.
Xs and Os vertical to one another are simultaneous.
R indicates random assignment to separate treatment groups.
Parallel rows unseparated by dashes represent comparison groups equated by randomization, while those separated by a dashed line represent groups not equated by random assignment.

14. CAMPBELL’S AND STANLEY’S SYMBOLIC REPRESENTATION OF ‘TRUE’ EXPERIMENTS
RO1 X O2
RO3 O4
Campbell, D. T. and Stanley, J (1963) Experimental and Quasi-experimental Designs for Research on Teaching. Boston: Houghton Mifflin Co.

15. TWO CONTROL GROUPS AND ONE EXPERIMENTAL GROUP PRETEST-POST-TEST DESIGN
Experimental RO1 X RO2
Control1 RO3 RO4
Control2 X RO5

16. THE POST-TEST CONTROL AND EXPERIMENTAL GROUP DESIGN
Experimental R1 X O1
Control R 2 O2

17. THE POST-TEST TWO EXPERIMENTAL GROUPS DESIGN
Experimental1 R1 X1 O1
Experimental2 R2 X2 O2

18. THE PRETEST―POST-TEST TWO TREATMENT DESIGN
Experimental1 RO1 X1 O1
Experimental2 RO3 X2 O4

19. THE TRUE EXPERIMENT ONE CONTROL AND TWO EXPERIMENTAL GROUPS
Experimental1 RO1 X1 O1
Experimental2 RO3 X2 O4
Control RO5 O6

20. THE PRE-TEST TWO TREATMENT DESIGN
Experimental1 RO1 X1 O1
Experimental2 RO3 X2 O4

21. MATCHED PAIRS DESIGN Step One: Measure the dependent variable.
Step Two: Assign participants to matched pairs, based on the scores and measures established from Step One.
Step Three: Randomly assign one person from each pair to the control group and the other to the experimental group.
Step Four: Administer the intervention to the experimental group and, if appropriate, a placebo to the control group. Ensure that the control group is not subject to the intervention.
Step Five: Carry out a measure of the dependent variable with both groups and compare/measure them in order to determine the effect and its size on the dependent variable.

22. 9 combinations: 1+4; 1+5; 1+6; 2+4; 2+5; 2+6; 3+4; 3+5; 3+6
FACTORIAL DESIGN
Performance in an examination may depend on availability of resources and motivation for the subject studied
INDEPENDENT VARIABLE
LEVEL
ONE
TWO
THREE
Availability of resources
limited availability (1)
moderate availability (2)
high
availability (3)
motivation for the subject studied
little
motivation (4)
moderate motivation (5)
motivation (6)
9 combinations: 1+4; 1+5; 1+6; 2+4; 2+5; 2+6; 3+4; 3+5; 3+6

23. Factorial designs must address the interaction of the independent variables.
Difference for motivation in mathematics is not constant between males and females, but varies according to age of participants: an interaction effect (age and sex)

24. PARAMETRIC DESIGN
Participants are randomly assigned to groups whose parameters are fixed in terms of the levels of the independent variable that each receives.
Parametric designs are useful if an independent variable has different levels or a range of values which may have a bearing on the outcome (confirmatory research) or if the researcher wishes to discover whether different levels of an independent variable have an effect on the outcome (exploratory research).

25. REPEATED MEASURES
Participants in the experimental groups are tested under two or more experimental conditions.
The order in which the interventions are sequenced may have an effect on the outcome (e.g. the first intervention may have an influence – a carry-over effect – on the second, and the second intervention may have an influence on the third).
Early interventions may have a greater effect than later interventions.
Repeated measures designs are useful if it is considered that order effects are either unimportant or unlikely.

26. REPEATED MEASURES (two groups receiving both conditions)
With no intervention
Matched on pre-test
Random allocation to groups
Group 2
With intervention
Post-test

27.       Independent groups Noise condition No noise condition
  
Sara Rob Peter
Jane Jack Jim
  
Joan Susan John
Lyn Sally Alan

28.       Repeated measures Noise condition No noise condition
  
Sara Rob Peter
Jane Jack Jim
  
Joan Susan John
Lyn Sally Alan
Sara Rob Peter

29. QUASI-EXPERIMENTS: NON-EQUIVALENT CONTROL GROUP DESIGN
Pre-experimental design: the one-group pretest―post-test
Experimental O1 X O2
Pre-experimental design: the one-group post-test only design
Experimental O1
The Post-Tests only non-equivalent groups design
Experimental O1
Control O2

30. QUASI-EXPERIMENTS: NON-EQUIVALENT CONTROL GROUP DESIGN
The pre-test―post-test non-equivalent group design
Experimental O1 X O2
Control O3 O4

31. PROCEDURES IN CONDUCTING EXPERIMENTS
Identify research problems
Formulate hypotheses
Select appropriate levels at which to test the independent variables
Decide which kind of experiment to adopt
Decide population and sampling
Select instruments for measurement
Decide how the data will be analyzed
Pilot experimental procedures
Carry out the refined procedures
Analyze results
Report the results

32. A TEN-STEP MODEL FOR CONDUCTING EXPERIMENTS
Step One: Identify the purpose of the experiment.
Step Two: Select the relevant variables.
Step Three: Specify the level(s) of the intervention (e.g. low, medium high intervention).
Step Four: Control the experimental conditions and environment.
Step Five: Select appropriate experimental design.
Step Six: Administer the pretest.
Step Seven: Assign the participants to the group(s).
Step Eight: Conduct the intervention.
Step Nine: Conduct the post-test.
Step Ten: Analyze the results.

33. PROCEDURES IN CONDUCTING EXPERIMENTS: HYPOTHESES
Null hypothesis (H1)
Alternative hypothesis (H0)
Direction of hypothesis: states the kind of difference or relationship between two conditions or two groups of participants
One-tailed (directional): e.g. ‘people who study in silent surroundings achieve better than those who study in noisy surroundings’
Two-tailed (no direction): e.g. ‘there is a difference between people who study in silent surroundings and those who study in noisy surroundings’

34. OPERATIONALIZING HYPOTHESES
Hypothesis: ‘people who study in quiet surroundings achieve better than those who study in noisy surroundings’
What do ‘work better’, ‘quiet’ and ‘noisy’ mean? Define the operations:
‘work better’ = obtain a higher score on the Wechsler Adult Intelligence Scale
‘quiet’ = silence
‘noisy’ = CD music playing
Operationalized hypothesis: ‘people who study in silence achieve a higher score on the Wechsler Adult Intelligence Scale than those who study with CD music playing’

35. DIRECTIONAL AND NON-DIRECTIONAL HYPOTHESES
Directional (one-tailed):
People who do homework without the TV on produce better results than those who do homework with the TV on.
Non-directional (two-tailed):
There is a difference between work produced in noisy or silent conditions.

36. TESTING VALIDITY AND RELIABILITY
MATURATION
HISTORY
TESTING
DIRECTION
OF CAUSALITY
INSTRUMENT-
ATION
THREATS TO
VALIDITY AND
RELIABILITY
TYPE 1 AND
TYPE 2
ERRORS
EXPERIMENTAL
MORTALITY
OPERATIONAL-
IZATION
CONTAMIN-
ATION
REACTIVITY

37. TIMING OF PRE-TEST AND POST-TEST
Pre-test: as close to the start of the experiment as possible (to avoid contamination of other variables).
Post-test: as close to the end of the intervention as possible.
Too soon a post-test: misses long-term/delayed effect and only measures short-term gain (which may be lost later).
Too long a time lapse before a post-test: becomes impossible to determine whether it was a particular independent variable that caused a particular effect, or whether other factors have intervened since the intervention, to produce the effect.

38. INTERNET-BASED EXPERIMENTS
Four types:
Those that present static printed materials (e.g. printed text or graphics)
Those that make use of non-printed materials (e.g. video or sound)
Reaction-time experiments
Experiments that involve some form of interpersonal interaction

39. INTERNET-BASED EXPERIMENTS
Check download speeds and time, anticipate problems of different browsers and platforms.
Can experience greater problems of dropout than conventional experiments.