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Constructing Research Design

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In a classroom experimentation be sensitive with the problem of EXTERNAL and INTERNAL validity. One way to avoid this problem is by using a control group. A control group refers to a group of Ss whose selection and experiences are exactly the same as the experimental group except that they do not receive the experimental treatment (Hatch and Farhady, 1982: 18)

Suppose the research is to investigate the effect of grammar correction on the writing skill in ESL students. INDEPENDENT VARIABLE: the amount of correction and the way correction is given on composition error. DEPENDENT VARIABLE: the degree of grammatical accuracy in Ss’ writing samples.

There are FIVE MAJOR classes of research design.

  1. Pre-experimental
    1. One-shot case study: Ss are given some treatment for a period of time and at the end they receive some sort of test. X  T
    2. One-group pretest posttest design. T1 X  T2
    3. Intact group design G1 X    T1

G2 T1

  1. True-Experimental

True experimental design have three basic characteristics (1) control group, (2) the Ss are randomly selected and assigned to the group, and (3) a pretest is administered to capture the initial differences between the groups.

  1. Posttest only control group

Initial differences between the groups are controlled for by the random selection and random assignment of the Ss

G1(random)    X    T1

G2 (random)         T1

  1. Pretest posttest control group design

G1(random)   T1 X    T2

G2 (random) T1 T2

  1. Quasi-experimental
    1. Time series design   T1 T2 T3 X T4 T5 T6
    2. Time –sample design T1 X T2 –   T3 T4 –  T5 X T6 –  T7 0 T8, etc
  1. Ex-post facto
    1. Correlational design, a group of Ss may give the data on two different variables T1 T2
    2. A criterion group design, two group are compared one  measure.

G1 T1

G2 T1

  1. Factorial design, has more than one independent variable/moderator variable

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