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Experimental research designs. ltst.ppt.

Experimental Research Designs with figures

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Experimental research designs. ltst.ppt.

  2. 2. EXPERIMENTAL RESEARCH DESIGNS An experiment typically involves a comparison of two groups (although some experimental studies have only one group or even three or more groups). Single-variable designs involves one independent variable (which is manipulated) and are classified as under:- I. Weak experimental research II. True experimental III. Quasi-experimental
  3. 3. WEAK EXPERIMENTAL DESIGNS Designs that are “weak” don’t have built-in controls for threats to internal validity. Four Examples of Pre-Experimental Designs are as under:- 1. One-Shot Case Study Design 2. One-Group Pretest-Posttest Design 3. Static -Group Comparison Design 4. Static-Group pretest-posttest Design
  4. 4. WEAK EXPERIMENTAL DESIGNS 1. THE ONE-SHOT CASE STUDY DESIGN In this design a single group is exposed to a treatment or event and a dependent variable is subsequently observed (measured) in order to asses the effect of the treatment. The One-Shot Case Study Design X O Treatment Observation (Dependent Variable) The most obvious weakness of this design is its absence of any control. The researcher has no way of knowing if the result obtained at O. Because the group has not been pretested in any way..
  5. 5. WEAK EXPERIMENTAL DESIGNS 2. THE ONE-GROUP PRETEST-POSTTEST DESIGN In this design, a single group is measured or observed not only after being exposed to a treatment of some sort, but also before. O X O Pretest Treatment Posttest This design is better than the one-shot case study, but it is still weak.
  6. 6. WEAK EXPERIMENTAL DESIGNS 3. THE STATIC-GROUP COMPARISON DESIGN In this design, two already existing, or intact, group, groups are used. This design is some times called a nonequivalent control design group design. X O O Line indicates that 02 groups being compared are already formed. X symbolizes the experimental treatment and blank space indicates that the “control” group doesn’t receive the experimental treatment.
  7. 7. WEAK EXPERIMENTAL DESIGNS 4.THE STATIC-GROUP PRETEST-POSTTEST DESIGN The static-group pretest-postest design differs from the static-group comparison only in that a pretest is given to both group. Diagram is as follows: O X O O O In analyzing the data, each individual’s pretest scores is subtracted from his/her posttest scores, thus permitting analysis of “gain” or “change”. In weak designs, it is the strongest design.
  8. 8. TRUE-EXPERIMENTAL DESIGNS The essential ingredient of a true experimental design is that subject are randomly assigned to treatment groups. Randomly assignment is a powerful technique for controlling the subject characteristics threat to internal validity. Its types are as under: The Randomized Posttest-Only Control Group Design The Randomized Pretest-Posttest Control Group Design The Randomized Solomon Four-Group Design
  9. 9. TRUE-EXPERIMENTAL DESIGNS 1, THE RANDOMIZED POSTTEST-ONLY CONTROL GROUP DESIGN This design involves two groups, both of which are formed by random assignment. One group receives the experimental treatment while the other does not, and then both groups are posttested on the dependent variable. Treatment Group R X O Control Group R C O In this design, the control of certain threats is excellent. This is perhaps the best of all designs to use in an experimental study, provided there are at least 30 subjects in each group.
  10. 10. TRUE-EXPERIMENTAL DESIGNS 2. THE RANDOMIZED PRETEST-POSTTEST CONTROL GROUP DESIGN The Randomized Pretest-Posttest Control Group Design differs from the Randomized posttest-only control group design solely in the use of a pretest. 02 groups of subjects are used, with both groups being measured or observed twice. The 1st measurement serves as pretest, the 2nd as the posttest. Random Assignment is used to form the groups. The measurement or observations are collected at the same time for both groups. Treatment Group R O X O Control Group R O C O
  11. 11. TRUE-EXPERIMENTAL DESIGNS 3. THE RANDOMIZED SOLOMON FOUR-GROUP DESIGN The Randomized Solomon Four-Group Design is an attempt to eliminate the possible effect of a pretest. It involves random assignment of subjects to four groups, with two of the groups being pretested and two not. One of the pretested group and one of the unpretested groups is exposed to the experimental treatment. All four groups are then posttested. Continued.
  12. 12. TRUE-EXPERIMENTAL DESIGNS 3. THE RANDOMIZED SOLOMON FOUR-GROUP DESIGN Cont…. Treatment group R O X O Control Group R O C O Treatment Group R X O Control Group R C O A weakness of this design is that it requires a large sample because subjects must be as signed to four groups
  13. 13. QUASI-EXPERIMENTAL DESIGNS Quasi-experimental designs do not include the use of random assignment. Researchers who employ these designs rely instead on other techniques to control threats to internal validity.  The Matching-Only Design  The Counterbalanced Design  The Time Series Design
  14. 14. QUASI-EXPERIMENTAL DESIGNS 1.THE MATCHING ONLY DESIGN This design differs from random assignment with matching only in the fact that random assignment is not used. The Matching-only postest-only Control group Design Treatment group. M X O Control Group M C O The Matching-only pretest-Posttest only Control group Design Treatment group. M O X O Control Group M O C O
  15. 15. QUASI-EXPERIMENTAL DESIGNS 2.THE COUNTERBALANCED DESIGN This design represent another technique for equating experimental and comparison groups. In this design, each group is exposed to all treatments, however many there are, but in a different order. Any number of treatments may be involved. Group I X1 O X2 O X3 O Group II X2 O X3 O X1 O Group III X3 O X1 O X2 O
  16. 16. QUASI-EXPERIMENTAL DESIGNS TIME SERIES DESIGN The typical pre-and posttest designs examined up to now involves observations or measurements taken immediately before and after treatment . A time series design, however involves repeated measurements or observations over a period of time both before and after treatment. O1 O2 O3 O4 O5 X O6 O7 O8 O9 O10 The effectiveness of the treatment in a time-series design is basically determined by analyzing the pattern of test scores that results from the several tests.
  17. 17. QUASI-EXPERIMENTAL DESIGNS FACTORIAL DESIGN Factorial Designs involves two or more independent variables, at least one of which is manipulated by the researcher. The 2x2 is the simplest factorial design. Factorial designs rarely include more than three factors. A factorial design is used to test whether the effects of an independent variable are generalizable across all levels or whether the effects are specific to particular levels (i.e., there is an interaction between the variables.)
  18. 18. FACTORIAL DESIGN This design extend the number of relationship that may be examined in an experimental study. They are essentially modifications of either the posttest- only control group or pretest-posttest control group designs, which permit the investigation of additional independent variables. Another value of a factorial design is that it allows a researcher to study the interaction of an independent variable with one or more other variables, sometimes called moderator variables.
  19. 19. FACTORIAL DESIGN Cont….. moderator variables may be either treatment variables or subject characteristic variable. Treatment group R O X YI O Control Group R O C YI O Treatment Group R O X Y O Control Group R O C Y O