Experimental Design:Experimental Design:An OverviewAn Overview

Mr. ReissfelderMr. Reissfelder

Lewiston High SchoolLewiston High School

What is Experimental Design?What is Experimental Design?

The way that an experiment The way that an experiment is set up to ensure that all is set up to ensure that all variables in all groups are variables in all groups are controlled (held constant) controlled (held constant) EXCEPT one.EXCEPT one.

What does Experimental Design What does Experimental Design allow us to do?allow us to do?

Test for cause and effect Test for cause and effect relationships between two relationships between two things being studied.things being studied.

What does Experimental Design What does Experimental Design allow us to do?allow us to do?

Show what happened Show what happened between the things being between the things being studied by obtaining and studied by obtaining and analyzing numbers (data) analyzing numbers (data) from each group in the from each group in the experiment.experiment.

What does Experimental Design What does Experimental Design allow us to do?allow us to do?

Make predictions about what Make predictions about what might happen in similar might happen in similar situations, then test them situations, then test them experimentally.experimentally.

Experimental Design- Experimental Design- PartsParts

An experiment is composed of An experiment is composed of VARIABLES & GROUPS:VARIABLES & GROUPS:

VARIABLES refer to VARIABLES refer to the way each the way each group is treatedgroup is treated and how they and how they react.react.

GROUPS refer to GROUPS refer to the conditions the conditions subjects are kept insubjects are kept in..

Experimental Design- Experimental Design- VariablesVariables

Variables are the many Variables are the many conditions found in groups in conditions found in groups in an experimentan experiment..

There are three types:There are three types:DEPENDENT VariableDEPENDENT VariableINDEPENDENT VariableINDEPENDENT VariableSTANDARDIZED VariablesSTANDARDIZED Variables

Experimental Design- Experimental Design- VariablesVariables

DEPENDENT VARIABLE DEPENDENT VARIABLE This is This is what is measured in the what is measured in the

experimentexperiment..Technically, it is the Technically, it is the effecteffect of the of the

independent variable acting on independent variable acting on the experimental group, the experimental group, measured in numbersmeasured in numbers (Data). (Data).

Experimental Design- Experimental Design- VariablesVariables

INDEPENDENT VARIABLE INDEPENDENT VARIABLE

This is This is the one thing that is the one thing that is differentdifferent between your between your control & experimental control & experimental groups.groups.

Experimental Design-Experimental Design-VariablesVariables

STANDARDIZED VARIABLESSTANDARDIZED VARIABLESThese are These are the conditions that the conditions that

stay the same stay the same (held constant) (held constant) in your control group & in your control group & experimental group or experimental group or groupsgroups..

Experimental Design-Experimental Design-Standardized VariablesStandardized Variables

Example:Example: In a study of different plant In a study of different plant foods on growth of radishes, some foods on growth of radishes, some typical standardized variables would typical standardized variables would be the…be the…

Amount / type of soil usedAmount / type of soil used Amount of light given to plantsAmount of light given to plants Amount of water given to plantsAmount of water given to plants Size / type of containers grown inSize / type of containers grown in Temperature / humidity of roomTemperature / humidity of room

Experimental Design-Experimental Design-GroupsGroups

There are two types of groups:There are two types of groups:A. CONTROL groupA. CONTROL groupB. EXPERIMENTAL groupsB. EXPERIMENTAL groups

Sometimes there is only one Sometimes there is only one experimental group; sometimes experimental group; sometimes there are many!there are many!

Experimental Design- Experimental Design- GroupsGroups

CONTROL GROUPS usually have CONTROL GROUPS usually have the normal, unchanged the normal, unchanged conditions (variables).conditions (variables).

There are two types of control There are two types of control groups:groups:

NEGATIVE CONTROLNEGATIVE CONTROLNORMAL CONTROLNORMAL CONTROL

Experimental Design- Experimental Design- Types of ControlsTypes of Controls

NEGATIVE CONTROL- This is NEGATIVE CONTROL- This is when conditions lack the one when conditions lack the one thing that is being studiedthing that is being studied..

This allows the researcher (you!) This allows the researcher (you!) to find out if something to find out if something otherother than your independent variable than your independent variable is actually causing the effect that is actually causing the effect that you’re seeing in your data!you’re seeing in your data!

Experimental Design- Experimental Design- Types of ControlsTypes of Controls

NORMAL CONTROL- This is NORMAL CONTROL- This is when the conditions are kept when the conditions are kept the way they normally are.the way they normally are.

This is often used in animal This is often used in animal studies to not harm them!studies to not harm them!

Experimental Design- Experimental Design- ControlsControls

Why use a normal control?Why use a normal control?For example, you can’t study the For example, you can’t study the

effect of temperature on goldfish effect of temperature on goldfish respiration rates with a negative respiration rates with a negative control. That would mean the control. That would mean the lack of temperature (freezing lack of temperature (freezing water!) & that’s unethical!!water!) & that’s unethical!!

Experimental Design- Experimental Design- GroupsGroups

EXPERIMENTAL GROUPS have all EXPERIMENTAL GROUPS have all the same variables as controls, the same variables as controls, but but ONEONE variable differs from the variable differs from the control.control.

The one variable that makes the The one variable that makes the experimental group (s) different experimental group (s) different from the control group is the from the control group is the independent variable!independent variable!

Experimental Design- Experimental Design- Levels of treatmentLevels of treatment

The number of experimental The number of experimental groups you will be studying is groups you will be studying is called the levels of treatment. called the levels of treatment.

It is when you use differing It is when you use differing amounts or strengths of the amounts or strengths of the Independent variable.Independent variable.