Experimental Designs
• Laboratory experiment- researcher creates a
situation with the desired condition and then
manipulates some variables whi...
Randomized designs
• Completely Randomized Designs (CRD)- an
experimental design that uses a random
process to assign expe...
Validity
• Internal validity: Is the effect due to our
hypothesized cause?
• External validity: Can we generalize to other...
Experimental designs
• X refers to the exposure of the subject to an
experimental treatment
• O refers to the process of o...
Extraneous variables
• History- specific events external to the
experiment but occurring at the same time ,
that may affec...
• Instrument variation- changes in the
instrument may account for the differences
• Statistical regression-the tendency of...
Pre experimental design
• One shot case study: X O
• One group pretest-post test design: O1 X O2
• Static group comparison...
True experimental designs
• Before-After with control group design
EG: (R) O1 X O2
CG: (R ) O3
O4
The difference between O...
Four group- six study design
•
•
•
•

EG 1:
CG 1:
EG 2:
CG 2:

O1 X O2 O2-O1 = E+U+I
O3
O4 O4-O3= U
X O5 O5- ½ (O1+O3)= E+...
Time series experimental designs
• Several observations taken before the
treatment; then the treatment (X) is
administered...
Factorial designs
• Allow for the testing of two or more treatments (factors) at
various levels.
• Main effect: the influe...
• A researcher wants to understand the
influence of both gender and the
advertisement (2 advts are beingconsidered)
on ‘be...
Latin square design
• Attempts to control or block out the
confounding effect of extraneous factors.
• A balanced two-way ...
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Experimental+designs

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Experimental+designs

  1. 1. Experimental Designs
  2. 2. • Laboratory experiment- researcher creates a situation with the desired condition and then manipulates some variables while controlling others. • A field experiment is a study in a realistic or natural setting and involves manipulation of the independent variable while carefully controlling the others
  3. 3. Randomized designs • Completely Randomized Designs (CRD)- an experimental design that uses a random process to assign experimental units to treatments • A Randomized Block Design- Grouping test units into homogenous blocks (similar to stratified sampling)
  4. 4. Validity • Internal validity: Is the effect due to our hypothesized cause? • External validity: Can we generalize to other samples?
  5. 5. Experimental designs • X refers to the exposure of the subject to an experimental treatment • O refers to the process of observation and measurement of the test units Eg: X O1 O2
  6. 6. Extraneous variables • History- specific events external to the experiment but occurring at the same time , that may affect the criterion variable • Maturation-Changes occurring within test units that are not due to the experimental variable but due to the passage of time • Testing-the experiment itself may affect the responses
  7. 7. • Instrument variation- changes in the instrument may account for the differences • Statistical regression-the tendency of the extreme cases to move closer to the average during the course of the experiment • Selection bias- the way in which the test units are selected
  8. 8. Pre experimental design • One shot case study: X O • One group pretest-post test design: O1 X O2 • Static group comparisonEG X O1 CG O2 No way of ensuring the two groups are equivalent prior to the comparison
  9. 9. True experimental designs • Before-After with control group design EG: (R) O1 X O2 CG: (R ) O3 O4 The difference between O3 and O4 reflects external causes. But they would exert a similar influence on EG also O2-O1= E+U O4-O3= U Design is nearly ideal. Accounts for all external causes except Interactive testing. So strictly: O2-O1=E+U+I O4-O3= U
  10. 10. Four group- six study design • • • • EG 1: CG 1: EG 2: CG 2: O1 X O2 O2-O1 = E+U+I O3 O4 O4-O3= U X O5 O5- ½ (O1+O3)= E+U O6 O6- ½ (O1+O3)= U
  11. 11. Time series experimental designs • Several observations taken before the treatment; then the treatment (X) is administered, then several observations are taken to measure if there is a change in the pattern after as compared to before the experiment • O1 O2 O3 X O4 O5 O6
  12. 12. Factorial designs • Allow for the testing of two or more treatments (factors) at various levels. • Main effect: the influence on a dependant variable by each independent variable separately • Interactive effect: the effect on a dependant variable by combinations of two or more independent variables • Interactive effects may be more than the total of the main effects
  13. 13. • A researcher wants to understand the influence of both gender and the advertisement (2 advts are beingconsidered) on ‘believability’. There are 2 independent variables: gender and advt. • Each variable has 2 levels (2 advts and 2 genders)- leads to a 2X2 factorial design
  14. 14. Latin square design • Attempts to control or block out the confounding effect of extraneous factors. • A balanced two-way classification scheme • In a Latin square design, both the confounding factors must have the same number of levels • Eg: A taste test involving 3 levels of tastes administered to 3 different people with the order of the administration randomized

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