This design allows for the testing of two or more hypotheses in a single project. There are three basic types of experimental research designs. The effect of the treatment would be equal to the level of the phenomenon after the treatment minus the level of the phenomenon before the treatment. You can use it if you are working with a very uniform field, in a greenhouse or growth chamber, or if you have no idea about the variability in your field. Accordingly we can name it as such and such —×— design.
It may, however, be remembered that the complex factorial design need not necessarily be of 2 × 2 × 2 type design, but can be generalised to any number and combination of experimental and control independent variables. This defect can, however, be removed by taking the means of rows and columns equal to the field mean by adjusting the results. Three replicates of each treatment are assigned randomly to 12 plots. The paired comparison is used to study two treatments. The sample is taken randomly from the population available for study and is randomly assigned to, say, four experimental and four control groups.
Means of different cells represent the mean scores for the dependent variable and the column means in the given design are termed the main effect for treatments without taking into account any differential effect that is due to the level of the control variable. For example, if an experiment requiring a two-way analysis of variance is replicated, it will then require a three-way analysis of variance since replication itself may be a source of variation in the data. The design can be represented thus: The main difficulty of such a design is that with the passage of time considerable extraneous variations may be there in its treatment effect. In split-plot design, one treatment the main plot—fallow or pea is split further into another treatment sub-plots of interest. For instance, an experiment has to be made through which the effects of five different varieties of fertilizers on the yield of a certain crop, say wheat, it to be judged. In other words, according to the principle of local control, we first divide the field into several homogeneous parts, known as blocks, and then each such block is divided into parts equal to the number of treatments.
The treatment is then introduced into the test area only, and the dependent variable is measured in both for an identical time-period after the introduction of the treatment. This layout works best in tightly controlled situations and very uniform conditions. For example, a college teacher compared the effect of the classsize as well as the introduction of the new instruction technique on the learning of research methodology. It is the simplest possible design and its procedure of analysis is also easier. The essential characteristic of the design is that subjects are randomly assigned to experimental treatments or vice-versa.
. Then there are two treatments of the experimental variable and two levels of the control variable. Thus, this random replication design is, in fact, an extension of the two-group simple randomized design. But the limitation of it is that the individual differences among those conducting the treatments are not eliminated, i. The variable selected for grouping the subjects is one that is believed to be related to the measures to be obtained in respect of the dependent variable. But this design suffers from one limitation, and it is that although each row and each column represents equally all fertilizer varieties, there may be considerable difference in the row and column means both up and across the field. This is a simple method for reducing the variability among treatment groups.
Of course, the greater the number of independent variables included in a complex factorial design, the higher the order of the interaction analysis possible. The groups compared have an equal distribution of characteristics and there is a high level of similarity among subjects that are exposed to different conditions. We illustrate some simple factorial designs as under: Illustration : 2 × 2 simple factorial design. Similarly, the row means in the said design are termed the main effects for levels without regard to treatment. The experimental group receives the treatment and both groups are post-tested to examine the effects of manipulating the independent variable on the dependent variable.
The degree to which the researcher assigns subjects to conditions and groups distinguishes the type of experimental design. To overcome such difficulties, the L. But at times, due to lack of historical data, time or a comparable control area, we should prefer to select one of the first two informal designs stated above. For example, if testing the effects of fertilizer on plant height, all other factors such as sunlight, soil type and water would have to be constant controlled. For example, they give information about such effects which cannot be obtained by treating one single factor at a time. We may briefly deal with each of the above stated informal as well as formal experimental designs. The following is a diagrammatic form of such a design in respect of, say, five types of fertilizers, viz.
Graphically it may take the following form: This model of a simple factorial design includes four treatments viz. In general, blocks are the levels at which we hold an extraneous factor fixed, so that we can measure its contribution to the total variability of the data by means of a two-way analysis of variance. Random replication design serves two purposes viz. All four groups will receive the post-test. But this does not control the differential effects of the extraneous independent variables in this case, the individual differences among those conducting the training programme. The data obtained in case of two 2 × 2 simple factorial studies may be as given in below. It is described in the section,.