Types of research; experimental

  • Created by: becky_99
  • Created on: 09-12-19 01:31

Experimental research

Establish cause and effect:

  • Cause must precede effect in time
  • Cause and effect must be correlated
  • Can do 1 study or multiple to try and establish cause and effect

Establish via:

  • Selection of good theoretical framework
  • Application of experimental design
  • Use of correct statistical model and analysis
  • Control of IVs
  • Measurement of DVs
  • Correct interpretation of results
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Internal vs. external validity


  • Did IV change DV?
  • Extent to which the results can be attributed to treatments used in the study
  • Ability to generalise results
  • Lab studies


  • To what populations, settings or treatments can the outcome be generalised?
  • Field studies
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Threats to interval validity

History - events that are not part of treatment.

Maturation - events due to passage of time.

Testing - effects of more than 1 test.

Instrumentation - change in calibration of measurements.

Statistical regression - selection based on extreme score.

Selection bias - non-random participant selection.

Experimental mortality - differential loss of participants.

Selection-maturation interaction - passage of time influencing groups differently.

Expectancy - experimenter's expectancy/anticipation of participants.

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Controlling threats to internal validity

Randomisation - allows the assumption that the groups do not differ at the beginning of the experiment.

Blind set-ups - method where participant doesn't know whether they are receiving the treatment or not.

Double-blind set-ups - method where both participant and experimenter don't know which treatment the participant is receiving.

Placebos - control group receives a false treatment and experimental group receives real treatment.

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Threats to external validity

Reactive of interactive effects of testing - pre-test may make participants sensitive to treatment.

Interaction of selection of biases and treatment - treatment may work only on participants selected on specific characteristics.

Reactive effects of experimental arrangements - setting constraints may influence generalisability.

Multiple-treatment interference - one treatment may influence the next treatment.

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Controlling threats to external validity

Remove pre-test.

Represent a larger population.

  • Participants
  • Treatments
  • Situations/settings
  • Tests

Multiple experimental groups.

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What is a true experiment?

A true experiment is where there has been manipulation of the IV and where units have been randomly assigned to the different levels of the IV.

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Types of research design

One-shot study:

     T     O

One-group pre-test post-test:

     O1     T     O2

Static group comparison:

     T     O1


(T - treatment; Blank - a control; O - observation; R - random allocation to groups; each line represents a group of subjects).

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Types of research design; true experimental

Randomised groups design:

R     T     O1

R            O2

Extending levels:

R     T1     O1

R     T2     O2

R              O3

Soloman's 4 group design: only experimental design that controls all threats to internal validity, but difficult to analyse statistically.

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Soloman's 4 group design

R     O1     T     O2     (group 1)

R     O3            O4     (group 2)

R               T     O5     (group 3)

R                      O6     (group 4)

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Causal-comparative vs. experimental research

ER - IV is manipulated by research.

CC - IV has already occurred.

ER - completely random groups.

CC - assignment to groups is based on pre-existing characteristics.

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CC vs. ER approach

Research question example: does aerobic training improve VO2 max?

CC approach: measure VO2 max in marathon runners and sedentary healthy controls and compare the results.

ER approach: randomly assign sedentary people to an aerobic training group for 12 weeks or 12 weeks of habitual physical activity; measure VO2 max before and after.

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Causal-comparative issues

Third variable - common cause.

Directionality - reverse causality.

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Conditions necessary for establishing cause & effe

Statistical relationship between IV and DV has been established:

  • ER = Yes
  • CC = Yes

X preceded Y in time:

  • ER = Yes
  • CC = ?

Other factors did not determine Y:

  • ER = YES
  • CC = ?

Because control over possible extraneous variables is partial in CC research, some people think it can be very misleading and shouldn't be used.

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Reliability and validity

Reliability: degree of consistency with which a measuring instrument measures whatever it's measuring.

Validity: degree to which a measuring instrument measures what it is meant to measure.

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Reliability & validity in action within sport scie

VO2 max (gold standard fitness test):

  • Expensive
  • Time consuming
  • Stressful for participant

Siconolfi's 3-minute step test:

  • Cheap
  • Easy to administer
  • Not physically demanding for participants
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