AIM = How and why are controlled experiments performed?

1
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)

2
Variables

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

3
Quantitative vs. Qualitative Data

• A Quantitative Variable is one that is measured
  using numbers.
• 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.
• Examples bright, clear, rough, smooth, pain.

4
Independent vs. Dependent Variables

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

5
Graphing Variables

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

6
Hypothesis vs. Theory

• Hypothesis is a testable statement that can be
  proven false.
• Can be a prediction of an outcome
• 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

7
Control

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

8
Francisco Redi Spontaneous Generation
OBSERVATIONS Flies land on meat that is left
uncovered. Maggots appear on the meat.
HYPOTHESIS Flies produce maggots.
Covered jars
Uncovered jars
VARIABLES
Controlled Variables jars, type of
meat, location, temperature, time
After several days
Independent Variables gauze (keeps flies away
from meat)
Dependent Variable whether maggots appear
Maggots appear
No maggots appear
CONCLUSION Maggots form only when flies come in
contact with meat. Spontaneous generation of
maggots did not occur.
9
(No Transcript)
10

• Lets 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 Pasteurs experiments?
• Try the Simulation

11
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.
12

• 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)