1. Experimental Design: An Overview Mr. Reissfelder Lewiston High School

2. What is Experimental Design?  The way that an experiment is set up to ensure that all variables in all groups are controlled (held constant) EXCEPT one.

3. What does Experimental Design allow us to do?  Test for cause and effect relationships between two things being studied.

4. What does Experimental Design allow us to do?  Show what happened between the things being studied by obtaining and analyzing numbers (data) from each group in the experiment.

5. What does Experimental Design allow us to do? MMMMake predictions about what might happen in similar situations, then test them experimentally.

6. Experimental Design- Parts  An experiment is composed of VARIABLES & GROUPS:  VARIABLES refer to the way each group is treated and how they react.  GROUPS refer to the conditions subjects are kept in.

7. Experimental Design- Variables  Variables are the many conditions found in groups in an experiment.  There are three types:  DEPENDENT Variable  INDEPENDENT Variable  STANDARDIZED Variables

8. Experimental Design- Variables  DEPENDENT VARIABLE  This is what is measured in the experiment.  Technically, it is the effect of the independent variable acting on the experimental group, measured in numbers (Data).

9. Experimental Design- Variables  INDEPENDENT VARIABLE This is the one thing that is different between your control & experimental groups. This is the one thing that is different between your control & experimental groups.

10. Experimental Design- Variables  STANDARDIZED VARIABLES  These are the conditions that stay the same (held constant) in your control group & experimental group or groups.

11. Experimental Design- Standardized Variables  Example: In a study of different plant foods on growth of radishes, some typical standardized variables would be the…  Amount / type of soil used  Amount of light given to plants  Amount of water given to plants  Size / type of containers grown in  Temperature / humidity of room

12. Experimental Design- Groups TTTThere are two types of groups: AAAA. CONTROL group BBBB. EXPERIMENTAL groups SSSSometimes there is only one experimental group; sometimes there are many!

13.  CONTROL GROUPS usually have the normal, unchanged conditions (variables).  There are two types of control groups:  NEGATIVE CONTROL  NORMAL CONTROL

14. Experimental Design- Types of Controls  NEGATIVE CONTROL- This is when conditions lack the one thing that is being studied.  This allows the researcher (you!) to find out if something other than your independent variable is actually causing the effect that you’re seeing in your data!

15. Experimental Design- Types of Controls  NORMAL CONTROL- This is when the conditions are kept the way they normally are.  This is often used in animal studies to not harm them!

16. Experimental Design- Controls  Why use a normal control?  For example, you can’t study the effect of temperature on goldfish respiration rates with a negative control. That would mean the lack of temperature (freezing water!) & that’s unethical!!

17. Experimental Design- Groups  EXPERIMENTAL GROUPS have all the same variables as controls, but ONE variable differs from the control.  The one variable that makes the experimental group (s) different from the control group is the independent variable!

18. Experimental Design- Levels of treatment  The number of experimental groups you will be studying is called the levels of treatment.  It is when you use differing amounts or strengths of the Independent variable.