AIM = How and why are controlled 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)

Variables A variable is a factor that can change. A variable can change other factors when it changes. A variable is a factor that can change. A variable can change other factors when it changes. Examples of variables: Examples of variables:-Temperature-Light-Time-Location-Elevation-Pressure

Quantitative vs. Qualitative Data A Quantitative Variable is one that is measured using numbers. A Quantitative Variable is one that is measured using numbers. Examples: temperature is measured in degrees, length can be measured in centimeters. Examples: temperature is measured in degrees, length can be measured in centimeters. A Qualitative variable is one that can not be measured in numbers, but by its qualities. A Qualitative variable is one that can not be measured in numbers, but by its qualities. Examples: bright, clear, rough, smooth, pain. Examples: bright, clear, rough, smooth, pain.

Independent vs. Dependent Variables The independent variable (IV) is the variable that is purposely changed (the variable under investigation) The independent variable (IV) is the variable that is purposely changed (the variable under investigation) aka: experimental / manipulated variable aka: experimental / manipulated variable The dependent variable (DV) is a factor that changes because the IV changes (the DV “depends” on the IV). The dependent variable (DV) is a factor that changes because the IV changes (the DV “depends” on the IV). aka: responding variable aka: responding variable Example: Elevation and Boiling temperature of water. The boiling temperature of water changes because of changes in elevation. Example: Elevation and Boiling temperature of water. The boiling temperature of water changes because of changes in elevation.

Graphing Variables The Independent variable is always graphed on the X axis. The Independent variable is always graphed on the X axis. The dependent variable is always graphed on the Y axis. The dependent variable is always graphed on the Y axis.

Hypothesis vs. Theory Hypothesis is a testable statement that can be proven false. Hypothesis is a testable statement that can be proven false. Can be a prediction of an outcome Can be a prediction of an outcome Hypothesis can become a theory once it is supported by enough evidence. Hypothesis can become a theory once it is supported by enough evidence. Theories are supported by multiple observations or experiments A theory may be proven false or modified when more data is collected Usually the least complicated explanations

Control The Control Group “stays the same” (or does not receive the independent variable under investigation) The Control Group “stays the same” (or does not receive the independent variable under investigation) The controlled variables are factors that do not change in the experiment. They remain constant (between the groups being tested). The controlled variables are factors that do not change in the experiment. They remain constant (between the groups being tested). In a Controlled experiment only one variable is allowed to change at a time. Everything else remains constant. In a Controlled experiment only one variable is allowed to change at a time. 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 & Spontaneous 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)