Single Group Design 3i242b

Single group design Presented by: Aya Ganongan Ian Alcazaren Mar Andrei Pascual Princess Lazarte

Single Group Design • The single group design is a design in which a group of subjects are istered a treatment and then measured (or observed). In experimental research, an experimental treatment should be given to the subjects, and then the measurement or observation made. Usually, with this design, an intact group of subjects is given the treatment and then measured or observed. No attempt is made to randomly assign subjects to the groups, nor does the design provide for any additional groups as comparisons. Thus, one group will be given one treatment and one "observation." This design is diagrammed as follows:

GP--T--O • The One-Shot Design is highly useful as an inexpensive measure of a new treatment of the group in question. If there is some question as to whether any expected effects will result from the treatment, then a one-shot may be an economical route. In cases where other studies, or the cumulative knowledge in the field provide information about either pre-treatment baseline measurements or behavior, the effects of other kinds of treatments, etc., the experimenter might sensibly decide that it si not necessary to undertake a more extensive design. Simplicity, ease, and low cost represent strong potential advantages in the oft-despised one-shot. This design answers only one question and that is in reference to post-treatment behavior, P1-1. It will describe the information about the behavior of the subjects shortly after treatment.

GP--O--T--O • The usefulness of this design is similar to that of the one-shot, except that an additional class of information is provided, i.e., pre-treatment condition or behavior. This design is frequently used in clinical and education research to determine if changes occurred. It is typically analyzed with a matched pairs t-test. • This design will answer the same question as the one-shot design P1-1, so that not only the posttreatment behavior of the subjects is answered, but it will also answer some questions in pre-treatment condition or behavior, namely P2-1 and P2-2.

Three Experimental Designs • To make things easier, the following will act as representations within particular designs: • X: Treatment • O: Observation or measurement • R: Random assignment • The three experimental designs discussed in this section are:

The One Shot Case Study • This is a single group studied only once. A group is introduced to a treatment or condition and then observed for changes which are attributed to the treatment • X O The Problems with this design are: • A total lack of control. Also, it is of very little scientific value as securing scientific evidence to make a comparison, and recording differences or contrasts. • There is also a tendency to have the error of misplaced precision, where the researcher engages in tedious collection of specific detail, careful observation, testing and etc., and misinterprets this as obtaining good research. However you can not misinterpret that a detailed data collection procedure equals a good design. • History, maturation, selection, mortality and interaction of selection and the experimental variable are all threats to the internal validity of this design.

One-Group, Pre-Post • In this design, one group is given a pre-treatment measurement or observation, the experimental treatment, and a post-treatment measurement or observation. The post-treatment measures are compared with their pre-treatment measures. This design is diagrammed as follows:

One Group Pre-Posttest Design • This is a presentation of a pretest, followed by a treatment, and then a posttest where the difference between O1 and O2 is explained by X: • O1 X O2 However, there exists threats to the validity of the above assertion:

• History: between O1 and O2 many events may have occurred apart from X to produce the differences in outcomes. The longer the time lapse between O1 and O2, the more likely history becomes a threat. • Maturation: between O1 and O2 students may have grown older or internal states may have changed and therefore the differences obtained would be attributable to these changes as opposed to X. • Testing: the effect of giving the pretest itself may effect the outcomes of the second test (i.e., IQ tests taken a second time result in 3-5 point increase than those taking it the first time). In the social sciences, it has been known that the process of measuring may change that which is being measured: the reactive effect occurs when the testing process itself leads to the change in behavior rather than it being a ive record of behavior (reactivity: we want to use non-reactive measures when possible).

• Instrumentation: examples are in threats to validity above • Statistical regression: or regression toward the mean. Timereversed control analysis and direct examination for changes in population variability are useful precautions against such misinterpretations. What this means is that if you select samples according to their extreme characteristics or scores, the tendency is to regress toward the mean. Therefore those with extreme high scores appear to be decreasing their scores, and those with extreme low scores appear to be increasing their scores. However this interpretation is not accurate, and to control for misinterpretations, researchers may want to do a time-reversed (posttest-pretest) analysis to analyze the true treatment effects. Researchers may exclude outliers from the analysis. • Others: History, maturation, testing, instrumentation interaction of testing and maturation, interaction of testing and the experimental variable and the interaction of selection and the experimental variable are also threats to validity for this design.

The Static Group Comparison • This is a two group design, where one group is exposed to a treatment and the results are tested while a control group is not exposed to the treatment and similarly tested in order to compare the effects of treatment.

X O1 O2

• Threats to validity include: • Selection: groups selected may actually be disparate prior to any treatment. • Mortality: the differences between O1 and O2 may be because of the drop-out rate of subjects from a specific experimental group, which would cause the groups to be unequal. • Others: Interaction of selection and maturation and interaction of selection and the experimental variable.