Fig. 2. Completely Randomized Design

And at the end of the experiment we will compare results from each treatment.

Fig. 3. Completely Randomized Design

Let’s see that a researcher believes that gender has an effect on the results. In a case like this we would use a Randomized Block Design that doesn’t immediately randomly assign the experiment units to receive treatments, we, first, assign people into a block based on the characteristic that’s expected to influence the response to its treatments. And this example where gender would be a blocking variable, so first we separate the experimental units based on gender, one block will be for females and one block will be for males. There are 18 females and 12 males (Fig. 4).