1. Chapter 15: Experimental Design
“See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirit of the world, and not according to Christ.”
Colossians 2:8

2. Introduction
Now that you have picked your question, made your hypothesis, and written your background, you are ready to figure out how you are going to do your experiment.
The following slides will help you decide how to do your experiment.
Vocabulary!
Investigator - that is you, the scientist 
Subject - the person, animal, or thing that agreed to be studied and participate in your experiment.
Intervention - an intervention is the thing (the variable) that you are giving to your subjects.
Ethical – means doing things for good. Do no harm. If you are unethical, you are doing bad things or things that are not in the best interest of the study subject.

3. How many arms should your study have?
The easiest answer is to have as many arms as there are things to compare.
For example, if you were trying to find out which method of disinfecting a dinner plate was the best, you might be able to think of 10 different ways to do it. However, maybe you are really only able to get the supplies to do five of those. In that case you should run a trial with 5 arms.
List in your notebook the different ways you can compare the items in your science fair project. How many of them can you really do? That will give you the number of arms you should have in your study.
Vocabulary!
Study arms - each individual item being studied. For example if you were studying which species of evergreen tree produced the sharpest needles, each arm would be each type of needle studied.

4. Should you have a control group?
A control group is a group of subjects that does not get the treatment or intervention.
Should you use one? The answer is always yes when you have an experiment that will lend itself to testing a normal situation versus something that you change. Most experiments will allow you to do this, however some will not.
Vocabulary!
Control - a group of subjects that do not receive any intervention. They either get nothing or they get what is considered the standard (normal) treatment. For example, if you were trying to determine if people who drink sugary drinks get more mosquito bites, you would want to compare them to a group that only drank water. Those that drank water only would be the control arm.

5. Should you have a control group?
Write down the groups you are going to compare in your project.
 Is there any way in your project to compare a group where you do nothing to it? Remember all other variables have to be the same Yes? No?
If you answered yes, then you should use a control group.
If you answered no, then you cannot use a control group.
Medical projects, chemistry, physics, some zoology and biology projects usually lend themselves to using control groups. Usually astronomy would be an area where control groups are harder to use, however it depends on the project and they are not impossible.

6. Should you have a control group? – What about a Placebo?
A placebo is a treatment that is given but it actually does not contain the treatment drug (can also be used with other kinds of interventions).
Should you give a placebo? You must be very careful!!! If you are giving a treatment to an animal or a person with a disease, it is unethical to withhold medications from that person. Their disease might get worse while you are running your experiments.
Does your experiment allow you to use a placebo Yes? No?
Write in your notebook about your control group and if your project allows for the use of a placebo.
Vocabulary!
Placebo – is something very much like a control. This term is usually used when administering a pill to someone or something but the pill does not contain any medication. It is most often a sugar pill. Sometimes it is called a blank.

7. Should you or your subjects be blinded?
Blinding your subjects and yourself can really help get accurate results.
If there is any way to blind your subjects, then you should do so. Remember, blinding doesn’t mean blindfolding, it really means being unaware of what treatment you are receiving.
Blinding is essential in a project where you are measuring human behavior. Humans alter their behavior if they know they are being watched. Your own expectations also change outcomes. You can unintentionally give more attention to the group you expect to prove your hypothesis.
Vocabulary!
Blinding - the investigator or subject does not know which treatment they are receiving.
Single Blind - only the subject or the investigator is blinded, not both.
Double Blind - both the subject and the investigator are blinded.

8. Should you or your subjects be blinded?
Write in your notebook about how you’ll use blinding in your experiment.
List your groups in your notebook:
Consider what possible ways you could blind your subjects so they don’t know what they are getting. Write down your solution in your notebook.
How can you blind yourself?
How can you blind your subjects?

9. Should you randomize your subjects?
Randomized subjects are those subjects that are picked at random to be given a certain treatment.
Here’s an example: If I have 21 children whose parents agreed to allow them to be tested to see if they slept less when drinking caffeine, then it would be a good idea to assign them numbers, put the numbers in a hat and draw them out one by one with your eyes closed. Have two piles and add the first number to the control pile so that child will get no caffeine. Add the second number to the second pile and that child will get caffeine. Go on this way until all numbers are drawn. In the end, the one pile will have the numbers of all the participants who are going to receive caffeine and the other will have the numbers of all the participants who will not receive caffeine.
Write in your notebook about how you’ll randomize your subjects.

10. Should you use a cross over design?
Cross over trials are excellent ways to compare results because the subject receives the treatment and then after a washout period, receives no treatment or vice versa. It is often used because the investigator eliminates the variation that exists between subjects.
Here is an example: If you wanted to see the effect of a new fertilizer on the growth of corn stalks, you could simply water them for two weeks and measure their growth every other day. Then you could add fertilizer for 2 weeks and measure their growth every other day. This means that the same plant received both the control and the actual treatment. You don’t really know if one plant grows differently than another simply because it is a different plant. This cross over eliminates that problem.
Write in your notebook if you can use a cross over design for your project and if so how?
Vocabulary!
Washout period – the time when the subject’s system is being cleared
of the previous treatment.
Cross over design – a trial where a subject is given nothing and then given a treatment or vice versa.

11. Should you use a parallel design?
A parallel design is great if you cannot cross the subjects over to another treatment or to the control.
A parallel design simply means you have your treatment arms and your control arms going on in different subjects usually at the same time.
It is important to try and match subjects as closely as possible in this design. For example, if you were testing hearing, it would be important not to use 6 year olds as controls and then do your treatment on 70 year olds. Their hearing is going to be a lot different even before your treatment.
Write in your notebook if you can use a cross over design for your project and if so how?
Warning – you cannot do both a cross over and a parallel design. You must pick one or the other.

12. Other Definitions & Your Project
Vocabulary!
Retrospective – Means a trial that looks back in time. This is often done when you are going back in medical records and looking at what happened to patients.
Prospective - Most science fair projects are prospective. That means you are currently doing the work and trying to find out what happens right now. It is a current project.
Consider the proper description for your study – which ones are you using? Make sure you write this down in your notebook

13. On A Final Note – Cross-sectional Study
A final study design that is often used in environmental studies and studies of disease is a cross sectional study. This is usually NOT a good design for science fair projects because you cannot tell what is causing what with any certainty.
The California Department of Public Health describes a cross-sectional study as a descriptive study in which disease and exposure status are measured simultaneously in a given population. Cross- sectional studies can be thought of as providing a "snapshot" of the frequency and characteristics of a disease in a population at a particular point in time. This type of data can be used to assess the prevalence of acute or chronic conditions in a population. However, since exposure and disease status are measured at the same point in time, it may not be possible to distinguish whether the exposure preceded or followed the disease, and thus cause and effect relationships are not certain.
We do not recommend cross sectional studies for most work. If you are considering doing a cross sectional study, please discuss this with your advisor to see if there might be another way to do the work before you begin.

14. Remember to write in your prayer journal and scientific notebook!!