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Experimental Design - pages 230-242 + 248-250

8 important questions on Experimental Design - pages 230-242 + 248-250

What do you do in the simplest type of experiment?

You create two groups that are equivalent to each other. One group (the program or treatment group) gets the program and the other group (the comparison group) does not. In all other respects the groups are treated in the same manner.

In the two-group posttest-only randomized experiment you are most interested in termining whether the two groups are different after the program. How?

Typically, you measure the groups on one or more measures and you compare them by testing for the differences between the means using a t-test (if you have just two groups) or one-way Analysis of Variance (ANOVA)(if you have two or more groups). CThis kind of analysis enables you to make a decision about whether any difference you observed between the groups is likely to be due to chance or not.

Difference between random selection and random assignment

Random selection refers to how sample members (study participants) are selected from the population for inclusion in the study. Random assignment is an aspect of experimental design in which study participants are assigned to the treatment or control group using a random procedure.
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Although there are a great variety of experimental design variations, we can classify and organize them using a simple signal-to-noise ratio metaphor.

In this metaphor, we assume that what we observe or see can be divided into two components, the signal and the noise (by the way, this is directly analogous to the true score theory of measurement). The figure, for instance, shows a time series with a slightly downward slope. But because there is so much variability or noise in the series, it is difficult even to detect the downward slope. When we divide the series into its two components, we can clearly see the slope.

We can now classify the experimental designs into two categories:

signal enhancers or noise reducers.

How are the signal-enhancing experimental designs are called?

The signal-enhancing experimental designs are called the factorial designs. In these designs, the focus is almost entirely on the setup of the program or treatment, its components and its major dimensions. In a typical factorial design we would examine a number of different variations of a treatment.

Analysis of covariance (ANCOVA)

An analysis that estimates the difference between groups on the posttest after adjusting for differences on the pretest.

Hybrid designs: switching – replications experimental designs.

A two group design in two phases defined by three waves of measurement. The implementation of the treatment is repeated in both phases. In the repetition of the treatment, the two groups switch roles: the original control group in phase 1 becomes the treatment group in phase 2, whereas the original treatment group acts as the control. By the end of the study, all participants have received the treatment.

The question on the page originate from the summary of the following study material:

Research Methods: The essential knowledge base | 9781133954774 | Trochim, et al

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Summaries related to Introduction to Design - pages 206-221