AIMAIM = = How and why are controlled How and why are controlled experiments performed?experiments performed?• Controlled experiments

are used to test hypotheses.

• Tests / investigates (changes) a single variable at a time (= the experimental / independent variable)

• The experimental group(s) receive the independent variable (IV)

• The control group is used for comparison (does not receive IV)

• All other variables are controlled (kept the same between the groups)

VariablesVariables A A variablevariable is a factor that is a factor that

can change. A variable can change. A variable can change other factors can change other factors when it changes.when it changes.

Examples of variables:Examples of variables:-Temperature-Temperature-Light-Light-Time-Time-Location-Location-Elevation-Elevation-Pressure-Pressure

Quantitative vs. Quantitative vs. Qualitative DataQualitative Data

A A QuantitativeQuantitative Variable is Variable is one that is measured using one that is measured using numbers.numbers. Examples: temperature is Examples: temperature is

measured in degrees, length measured in degrees, length can be measured in can be measured in centimeters.centimeters.

A A QualitativeQualitative variable is one variable is one that can not be measured in that can not be measured in numbers, but by its qualities. numbers, but by its qualities. Examples: bright, clear, rough, Examples: bright, clear, rough,

smooth, pain. smooth, pain.

Independent vs. Dependent Independent vs. Dependent Variables Variables

The The independent variable (IV)independent variable (IV) is the is the variable that is purposely changed (the variable that is purposely changed (the variable under investigation) variable under investigation) aka: aka: experimental / manipulated variableexperimental / manipulated variable

The The dependent variable (DV)dependent variable (DV) is a factor that is a factor that changes because the IV changes (the DV changes because the IV changes (the DV “depends” on the IV).“depends” on the IV). aka: aka: responding variableresponding variable

Example:Example: Elevation and Boiling temperature Elevation and Boiling temperature of water. The boiling temperature of water of water. The boiling temperature of water changes because of changes in elevation. changes because of changes in elevation.

Graphing VariablesGraphing Variables

The The Independent variableIndependent variable is always is always graphed on the graphed on the X axisX axis. .

The The dependent varidependent variableable is always is always graphed on the graphed on the Y axisY axis. .

Boiling Temperature of water

180

185

190

195

200

205

210

215

0 2000 4000 6000 8000 10000 12000 14000 16000

Feet above sea level

Deg

rees

F

Hypothesis vs. TheoryHypothesis vs. Theory

HypothesisHypothesis is a is a testable statement testable statement that can be proven that can be proven false.false.

Can be a prediction Can be a prediction of an outcomeof an outcome

Hypothesis can Hypothesis can become a theory become a theory once it is supported once it is supported by enough evidence. by enough evidence.

TheoriesTheories are are supported by supported by multiple observations multiple observations or experimentsor experiments

A theory may be A theory may be proven false or proven false or modified when more modified when more data is collecteddata is collected

Usually the least Usually the least complicated complicated explanationsexplanations

ControlControl

The The Control GroupControl Group “stays the same” “stays the same” (or does not receive the independent (or does not receive the independent variable under investigation)variable under investigation)

The The controlled variablescontrolled variables are factors are factors that do not change in the experiment. that do not change in the experiment. They remain constant (between the They remain constant (between the groups being tested). groups being tested).

In a In a Controlled experiment Controlled experiment only one only one variable is allowed to change at a time. variable is allowed to change at a time. Everything else remains constant. Everything else remains constant.

OBSERVATIONS: Flies land on meat that is left uncovered. Maggots appear on the meat.HYPOTHESIS: Flies produce maggots.

VARIABLES

Controlled Variables:jars, type of meat,location, temperature,time

Independent Variables:gauze (keeps flies away from meat)

Uncovered jars Covered jars

After several days

Maggots appear No maggots appear

Dependent Variable: whether maggots appear

CONCLUSION: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur.

Francisco Redi & Francisco Redi & Spontaneous GenerationSpontaneous Generation

Let’s Practice: Disproving “Spontaneous Generation”

Discussion:-What is spontaneous generation?-Describe how Redi set-up his experiment.-Identify the variables involved (IV, DV, CV)-Analyze the data produced Make Conclusion-What do you know about Pasteur’s experiments?

Try the Simulation

EXPERIMENTAL DESIGN PROJECT: HOME REMEDIES

BACKGROUND:Recall that a hypothesis is an educated guess (or

an explanation that is proposed for a phenomenon). Think of your hypothesis as your suggested answer to a question, solution to a problem, or statement of a relationship. A hypothesis should be testable – and may be in the form of an “if – then” statement that identifies the relationship.

In a controlled experiment, the same experiment is performed twice. Both of these experiments should be set-up and treated the same --- except for the one variable under investigation (this is the independent variable). If the results of the two set-ups (the 2 groups) are different, this difference is likely due to the experimental variable that is changed. A controlled experiment involves at least 2 groups: the experimental group(s) (receives IV) and the control group.

REMEDY EXAMPLES:- salt water gargle reduces sore throat pain- chicken soup reduces the duration of a cold- other ideas…?

EXAMPLE:

•Hypothesis (if-then statement that is testable)(if patients gargle with salt water, their throat will improve)•IV / DV / CV (know the variables)(IV = salt water; DV = throat pain; CV = patients)•Set-up Experimental + Control Group(Exp. Group = salt water; Control Group = none)•Data (how to collect, organize, analyze)(set up appropriate data table – but do not create data)•Support for hypothesis…?(if remedy is effective, the Exp. Group should improve)