Experimental Research Designs

1. Experimental Research Designs Dr Leena KC Dean ,Yenepoya Nursing college, Mangalore

2. Experimental Research • Researcher’s role vis-à-vis study participants • In some studies researcher wants to test the effects of a specific intervention • Such studies are experimental studies • The researcher play an active role by introducing the intervention • Researchers are active agents & not passive observers

3. Characteristics of true experiments • Manipulation: experimenter does something to at least some subjects • Control: experimenter introduces controls over the experimental situation including use of a control group • Randomization: experimenter assigns subjects to a control or experimental group on a random basis

4. Manipulation • Involves doing something to study participants (Independent variable) • Experimental treatment • Intervention • Vary the IV and observe effect on the DV • Cause and effect

5. Control • Achieved by • Manipulating • Randomizing • Carefully preparing experimental protocols • Using a control group

6. Control group • Group of subjects whose performance on a DV is used to evaluate the performance of the experimental group (treatment group) on the same DV

7. Randomization (random assignment) • Placing subjects in groups at random. • Random: every subject has an equal chance of being assigned to any group • No systematic bias in the group with respect to attributes that could affect the DV

8. Methods of randomization • Flipping a coin • Matching • Draw of lots (pulling names from a hat) • Table of random numbers • Cluster randomization: reduces possibility of contamination • Computer generated random numbers: • Randomization.com

9. Randomization.com!!! (where it's never the same thing twice) There are three randomization plan generators. • The first (and original) generator randomizes each subject to a single treatment by using the method of randomly permuted blocks. • The second generator creates random permutations of treatments for situations where subjects are to receive all of the treatments in random order. • The third generator generates a random permutation of integers. This is particularly useful for selecting a sample without replacement.

10. Control over independent variable • Experimental • Quasi experimental • Pre-experimental • Non experimental

11. Is there an intervention? (control over the IV) No yes Non experimental research Is there random assignment to treatment groups? Yes Experimental research

12. Is there an intervention? (control over the IV) yes No Non experimental research Is there random assignment to treatment groups? No Yes Are there efforts to compensate for the lack of random assignment Experimental research Yes No Pre-experimental research Quasi experimental research

13. Experimental designs

14. Basic experimental designs • Pretest- posttest design (before-after design) • Posttest only design (after-only design) • Solomon four- group design • Factorial design • Randomized block design • Crossover design (repeated measure design)

15. Pretest- posttest design (before-after design) • Classic experimental design • Most commonly used • Two randomized groups • One group receives the experimental treatment • Other group receiving no treatment, a placebo treatment, or the usual treatment

16. Pretest- posttest design (before-after design) • Comparison of the pretest scores allows evaluation of the effectiveness of randomization • Treatment is under the control of the researcher • The dependent variable is measured twice, before & after the manipulation of the independent variable • Comparison of the posttest scores allows determining the effect of the independent variable

17. Pretest- posttest design (before-after design) Group Pretest Intervention Posttest R C O1 O2 R E O1 X O2

18. Pretest- posttest design (before-after design) • Impact of an adaptation training program for patients with end stage renal disease. Shiow, Yuh & Ching Lee (2005) • 57 patients randomly assigned to two groups • Intervention:Adaptation training program: group sessions over 8 week period & monthly follow up • Controlgroup received usual care • Outcome measure: QOL, HD stressor scale, depression inventory, medical outcomes at 0 & 3 months

19. Pretest- posttest design (before-after design) • Effectiveness of accupressure in improving dyspnea in COPD patients • 44 patients randomly assigned to two groups • Intervention:true accupoint pressure, 5 sessions per week & 16 minutes per session. 20 sessions over 4 weeks period • Controlgroup: accupressure using sham pressure points for the same duration • Outcome measure: pulmonary function status, dyspnea questionnaire, anxiety & 6 minute walk test, at 0 & 4 wks

20. Posttest only design (after-only design) Group Pretest Intervention Posttest R C O R E X O

21. Posttest only design (after-only design) • Effect of two nursing interventions in preventing occurrence of angular stomatitis on orally intubated patients. Rani Jose (2005) • 40 patients randomized to two treatment groups (odd & even numbers) • E1 Angle changing 12 hrly • E2 Hydrocolloid application at the angle without changing the position • E1 Daily assessment of angle & lips • E2 Assessment of angle & lips on day 3

22. Posttest only design (after-only design) Group Intervention Posttest R E1 X1 O R E2 X2 O

23. Posttest only design (after-only design) • Effect of a new educational strategy on students’ attitudes towards patients • Reduces the effect of pretest sensitization

24. Solomon four group design • Involves two experimental groups & two control groups • One experimental & one control group are administered pretest & other groups are not • Allows the effects of pretest measure & intervention to be segregated

25. Solomon four- group design Group Pretest Intervention Posttest C O1 O2 C O2 E O1 X O2 E X O2

26. Factorial design • Used to manipulate two or more independent variables simultaneously • Independent Variables - Factors • Each factor – levels (two or more) • Treatment condition – cell (Box) • Designs - 2 x 2, 2 x 3, 3 x 3, 3 x 4

27. Factorial design (2X3)

28. Factorial design (2X3)Intervention for pain relief in cancer patients

29. Randomized block design • Similar to factorial design • Two Factors • One factor not experimentally manipulated -Blocking variable • Designs- 2 X 2, 2 X 3, 2 X 2 X 2

30. Randomized block design (2x2)

31. Crossover design (repeated measure or counterbalanced design) • Involves exposure of same subjects to more than one experimental treatment • Subjects are randomly assigned to different orderings of treatment • Subjects serve as their own control • Extremely powerful design but inappropriate for certain types of research due to problem of carry-over effects

32. Crossover design • Effects of soy protein rich diet on renal function in young adults with insulin dependent DM. Stephenson et al (2005) • 12 Type I DM patients • 4 weeks assessment of baseline data • Assigned to soy or control diet for 8 weeks • Crossed over to alternative diet for 8 wks • Outcome measures: GFR, LDL cholesterol, urinary excretion of soy isofavones at the end of each 8 wk period

33. Experimental condition(formal protocol) • What is the intervention? How does it differ from usual methods of care? • If there are two alternative interventions, how exactly do they differ? • What are the specific procedures to be used with those receiving the intervention? • What is the dosage or intensity of the intervention

34. Experimental condition • Over how long a period will the intervention be administered, how frequently it will be administered, and when will the treatment begin? • Who will administer the intervention? What are their credentials, and what type of special training will they receive? • Under what conditions will the intervention be withdrawn or altered?

35. Control condition • Control group condition used as a basis of comparison in a study is referred to as the counterfactual • An alternative intervention • A placebo or psuedointervention presumed to have no therapeutic value • Standard methods of care • Different doses or intensities of treatment • Delayed treatment

36. Control condition • Needs to be as carefully spelt out as the intervention • Explain what the condition was & how different it was from the intervention being tested