Experimental design


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Experimental design

  1. 1. Intact Group Design andTrue ExperimentaldesignPresenter : Minh Sang
  2. 2. Intact Group Design This is the design that most classroom researchers use. Step 1 : Select 2 classes to make 2 groups. One is experimental group and the other is control group ( You can decide it by the flip of a coin ) Step 2 : You give the treatment ( experimental instruction ) to the experimental group, not the control group
  3. 3. Intact Group Design Step 3 : Give the 2 groups a posttest. After the posttest, we can have the result for the research. In short, an intact group design is : G1 x T1 G2 T1G1 : Experimental GroupG2 : Control GroupT1 : Posttest
  4. 4. Intact Group Design Example : You want to investigate the effect of grammar correction on the writing skills of ESL students Step 1 : Select two similar groups of ESL ss. Flip the coin to decide which group is the experimental and control group Step 2 : Give the Exp Group the treatment ( grammar correction ) and do nothing with the Control group.
  5. 5. Intact Group Design Step 3 : Give a pottest to 2 groups. After the test, you will have a conclusion that grammar correction is effective or not ( If the Exp Group has the higher scores, it means that your treatment – grammar correction is effective )
  6. 6. True Experimental Design This design is used for situations in real life, when we don’t have any particular groups or classes, teams for our research. It is similar to the intact group design. and you may have a pretest for the Pretest pottest control group design
  7. 7. True Experimental Design Pottest only control group : this is nearly the same as the the intact group design. The difference is that we choose the members for the group randomly :So we have : G1 ( random ) X T1 G2 ( random ) T1
  8. 8. True Experimental Design Pretest pottest control group design : We may have a pretest for this design : G1 ( random ) T1 X T2 G2 ( random ) T1 T2So why do we have the T2 ( prettest ) ?
  9. 9. True Experimental Design The T2 ( prettest ) is given when the time you have between the prettest and pottest is not considerable ( not sufficient ) and it may affect the conclusion of your research.  It is when you give a prettest to test the knowledge, ability…of the 2 groups that you have. After all, your conclusion should be much more defensible.
  10. 10. QUASI-EXPERIMENTAL DESIGN Presenter: Minh Dang
  11. 11. • Quasi-experimental design is practical compromises between true experimentation and which we wish to investigate.
  12. 12. • Quasi-experimental design is susceptible (easily effected) to some of the questions of internal and external validity
  13. 13. • By using Quasi-experimental design, we control as many variables as we can and also limit the kinds of interpretations we make about cause-effect relationships and hedge the power of our generalization statements
  14. 14. Time-series design• Because of limitations  sometimes it is impossible to have a control group•  use time-series design to deal with the lack of control group
  15. 15. • Time-series design use several pretest and several postest• No treatment during the pretests  know the changes when there are no treatments• After some pretests  treatment  some posttests  changes from the treatment•  more accurate comparison, conclusion
  16. 16. • Line 1: no effect• Line 2: negative effect• Line 3: positive effect  treatment is effective
  17. 17. Equivalent time sample design• The treatment is introduced and reintroduced between every other pretests and posttests• Test 1  treatment  test 2  treatment  test 3 treatment  …
  18. 18. In short• Quasi-experimental design: control many variables and reduce limitations• Time-series design: pretests  treatment  posttests• Equivalent time-sample design: test  treatment  test  treatment  …
  19. 19. EX POST FACTO DESIGNS Presenter: Huu Loc
  20. 20. EX POST FACTO DESIGNS When researchers control the threats to internal and external validity, they are trying to find a direct relationship between the independent and dependent variables. In other words, they select the population, sample, treatments, and variables in order to find a cause-and- effect relationship between the variables.
  21. 21. exampleYou may have created a series of media lessonson how to say no to requests in English.Not randomly select Can not draw causalyour Ss, organize relationshipsyour control and between your mediatreatment groups, materials and Ssand control for improvement infactors aside from ability to turn downthe media lessons requests gracefully inwhich might English.influence the results
  22. 22. When considering all the factors that you would need to control, you might think that designing a true experimental research project is almost impossible.But , it should not mean that we have to giveup approximating the ideal as much aspossible. X causes Y is an extremely difficult thingto do unless the research is carefullydesigned and as many extraneous factorsare controlled as possible.
  23. 23. When there is no possibility of randomselection of Ss, instead of abandoning theresearch, we simply have to limit the domainof our claims.oWe have to avoid making cause and effectstatements.
  24. 24. EX POST FACTO designs are often usedwhen the researcher does not havecontrol over the selection andmanipulation or the independentvariable.  Researchers look at the type and/or degree of relationship between the two variables rather than at a cause-and- effect relationship.
  25. 25. example We can study the relationship between scores on a school- leaving exam in ESL and teachers ratings for the Ss using an ex post facto design. We can see if there is a certain amount of agreement between the two sets of scores. Any relationship between the scores of the groups would not be related to any instructional program we had given them before the test. The designs are called ex post facto. The researcher has no control over what has already happened to the Ss. The treatment has been given prior to the research project.
  26. 26. There’re 2 EX POST FACTO designs o Correlational designs o Criterion group design
  27. 27. Correlational designs are the mostcommonly used subset, in which a group ofSs may give us data on two differentvariables.o For example, students planing to study in the US take the TOEFL. Many universities also have entrance exam to administer to students. We can then look at the relationship of Ss’ scores on one test to their scores on the other.o Or, foreign students may be asked to take both the Graduate Record Exam (GRE) and an English placement exam prior to admission to a university.o The score for each S on one test can be compared with the score on the other, allowing us to see whether whose students who score high on one lest also score high on the other.
  28. 28. The schematic representation of thisdesign would be T1 T 2
  29. 29. • It’s no causal relationship between the two variables --> the distinction between independent and dependent variables is not well defined.• It is arbitrary to call one or the other the independent variable.• But, it is usually the case that the investigator may be more concerned with one than the other and may therefore label the first the independent variable and the second the dependent variable and show this by the labels X and Y.
  30. 30. In a CRITERION GROUP DESIGN, twogroups of Ss are compared on onemeasure. In this design, two groups of Ss are compared on one measure. With this design, you might, for example, measure the reading peed of Iranian and French students, assuming you want to see how related or different they might be.
  31. 31. The design would look like this:G1 T1G2 T1
  32. 32. You can change the design into a two-criterion design by considering level oflanguage proficiency as well as their nativelanguage.In this case the criterion group design formsa factorial design.
  33. 33. FACTORIAL DESIGNS Presenter: Ngan Giang
  34. 34. DEFINITION• Is simply the addition of more variables to the other designs• There will be more than one independent variable considered• The variables may have one or many levels
  35. 35. 2 x 2 example Room Temperature Test Difficulty (Level) 50 degrees (Level) 90 degrees (Level) Hard Test Hard Test in 50 degrees Hard Test in 90 degrees (Level) Easy Test Easy Test in 50 degrees Easy Test in 90 degreesWe are interested in studying the effect of room temperatureon test taking. To do this, we compare test scores of studentswho take a test in a 90 degree room vs. those who take a testin a 50 degree room.
  36. 36. • Factor 1: Treatment – psychothera py – behavior modification• Factor 2: Setting – inpatient – day treatment – outpatient
  37. 37. • higher scores mean the patient is doing worse. • day treatment is never the best condition.• psychotherapy works best with inpatient care and behavior modification works best with outpatient care.
  38. 38. THE PROS AND CONS• Factorial designs are extremely useful to psychologists and field scientists as a preliminary study, allowing them to judge whether there is a link between variables, whilst reducing the possibility of experimental error and confounding variables .• The factorial design, as well as simplifying the process and making research cheaper, allows many levels of analysis. As well as highlighting the relationships between variables, it also allows the effects of manipulating a single variable to be isolated and analyzed singly.• The main disadvantage is the difficulty of experimenting with more than two factors, or many levels. A factorial design has to be planned meticulously, as an error in one of the levels, will jeopardize a great amount of work.
  39. 39. Summary1. What is experimental design?2. Types of experimental design: – Pre-experimental design – True experimental design – Quasi-experimental design – Ex post facto design – Factorial design
  40. 40. Thanks for your attention!• Group 5: 1. Dinh Quoc Minh Dang 2. Vo Huu Loc 3. Nguyen Dinh Minh Sang 4. Nguyen Ngoc Cam 5. Tran Thi Ngan Giang