An experiment is performed to test the effects of a new drug o...

Question

An experiment is performed to test the effects of a new drug on attention-deficit/hyperactivity disorder (ADHD). The experimenter identifies 320 people ages 7 to 44 with ADHD to participate in the experiment. The subjects are divided into equal groups according to age. Within each group, subjects are then randomly selected to be in either the treatment group or the control group. What type of experimental design is being used for this experiment?

Accepted Answer

Hello there. Today we're gonna solve the following practice problem together. So first off, let us read the problem and highlight all the key pieces of information that we need to use in order to solve this problem. A fitness researcher wants to compare two exercise programs. She recruits 160 volunteers and first separates them into groups based on whether they exercise regularly or not. Within each group, volunteers are randomly assigned to one of the two exercise programs. What type of experimental design is this? Awesome. So it appears for this particular prom, based on all the information that is provided to us by the prom itself, we're asked to determine what type of experimental design is this. So now that we know we're ultimately trying to solve for, let's read off our multiple choice answers to see what our final answer might be. A is completely randomized design. B is randomized block design. C is matched pairs design, and D is factorial design. Awesome. So in order to solve this problem, let's take a moment to define each of our multiple choice answers. So let us define these different experimental designs, starting with completely randomized design. So as we should recall for the completely randomized design, which we can denote this or abbreviated as CRD, once again, completely randomized design. The definition is, as we should recall, all subjects are randomly assigned to different treatment groups without any prior grouping. And we use this particular experimental design when the population is fairly homogeneous, meaning it's consistent throughout. So, for example, 100 people are are randomly assigned to either a new drug group or a placebo group, for an example. So with that in mind, our next design experimental design we're going to investigate is the randomized block design, which we'll call RBD for short. And as we should recall, the definition of randomized block design is subjects are first grouped or blocked by a characteristic, for example, age, gender, exercise habits. Then randomly assigned two treatments within each block. And as we should recall, this experimental design is used when you want to control for a variable that might affect the results. And an example of this particular design is blocking by gender before assigning to a different diet plan. Fantastic. Our next design is matched pair designs, which I'll call MPD for short, and for the matched pair designs, as we should recall, is defined as each subject is matched with themselves before and after treatment. Or with another similar subject and both receive different treatments and as we should recall this particular design is used when comparing two treatments in paired or. Very similar subjects. And an example of this particular design is each person tries two diets for 1 month each or twins receive different medications. Awesome. And our last design we're going to investigate, as we should recall and note, is the definition for factorial design, which I'll call FD for short. And the definition of factorial design is experiments that involve more than one factor, and all combinations of levels of the factors are tested. And this is used when studying interactions between two or more variables. And an example of this particular experimental design is when testing the effects of diet, low versus high fat and exercise, yes versus no, on weight loss, for example, a 2x2 design. So, with these different experimental designs in mind for our given problem investigating the pieces of information that are given to us, firstly, we need to note that volunteers are grouped into blocks based on their regular exercise habits. Secondly, we need to note that within each block, volunteers are randomly assigned to one of the 2 exercise programs. And thirdly, we need to note that this is a randomized block design because blocking is done by exercise habits and randomization is done within each block. So that will mean our final answer, without a doubt, is multiple choice answer letter B, randomized block design, and that's it. We've officially solved for this problem. Thank you so much for watching. Hopefully that helped, and I can't wait to see you in the next video. Bye.

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Key Concepts

Randomized Controlled Trial (RCT)

Stratified Sampling

Control Group

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