Experimental Design – Important, Unforgettable Definitions
Name: _____________________
Independent Variable (IV) – The variable that the Investigator will purposely manipulate (change).
Dependent Variable (DV) – The variable that may change, Depending on how the investigator changes the
independent variable.
Hypothesis – an educated guess of how the dependent variable will change when the independent variable is
manipulated. Usually worded as follows: If the IV is …….., then the DV will …….
Control - a group of experimental subjects that is not exposed to a chemical or treatment being investigated
so that it can be compared with experimental groups that are exposed to the chemical or treatment. It is
also the standard of comparison.
Constants - factors in an experiment that are kept the same in both the experimental and the control groups,
and not allowed to change or vary.
Source of Error - a limitation of a procedure or an instrument that causes an inaccuracy in experimental
findings
Data - evidence; information gathered from observations
Observation - Use of one or more of the five senses (sight, sound, etc.) to gather information
EXAMPLE
Glucose is a sugar that is the cell’s main source of energy.
A student decided to see whether increasing the amount of sugar in his cereal would allow him to do more
push-ups. Every day of the week, at 6 a.m. , he ate 2 cups of cornflakes with 1 cup of milk. He added
different amounts of sugar to the cereal and milk, as follows:
Monday – added 1 teaspoon sugar
Wednesday – added 3 teaspoons sugar
Tuesday – added 2 teaspoons sugar
Thursday – added 4 teaspoons sugar
On Friday he added no sugar to the cereal and milk. Each day at 8 a.m, he counted how many push-ups he was
able to do.
IV –
Amount of sugar added to cereal
DV –
The number of push-ups the student can do
Hypothesis – If the amount of sugar in cereal is increased, then the number of push-ups the student can do
will increase.
Control – cereal with no sugar added
Constants – brand of cereal, amount of cereal, amount of milk, time of day cereal is eaten, time of day pushups are done
Sources of Error – accuracy of teaspoon and cup measurements; does not take into account amount of sleep
student had, or other food he ate the day before.
Practice #1
A student noticed that on a hot, sunny summer day at the beach, an empty soda can became too
hot to touch. She also noticed that an empty soda can her little brother had filled with water
became warmer, but not hot.
She decided to take 6 empty soda cans and fill them with varying amounts of water, as follows:
Can 1 – added 10 ml. water
Can 4 – added 40 ml. water
Can 2 – added 20 ml. water
Can 5- added 50 ml. water
Can 3 – added 30 ml. water
Can 6 – added 60 ml. water
She took a 7th empty can, and added no water to it. She also placed a thermometer into each
can. She then set the cans on a picnic table at the beach, in the sun.
After the cans had been in the sun for 2 hours, she measured the temperature in oC for each
can.
1. What was the student’s hypothesis?
2. What was the IV?
3. What was the DV?
4. What was the control?
5. What were the constants?
6. What are possible sources of error?
Practice #2
Design an experiment in which you will see how the amount of butter added to breakfast toast
affects a student’s ability to do sit-ups each day.
1. What is the IV?
2. What is the DV?
3. What is your hypothesis?
4. What will be your control?
5. What will be your constants?
6. What are possible sources of error?
7. Briefly describe the set-up of your experiment (i.e, When will the toast be eaten, when will
the sit-ups be done, ETC.?)