Experimental Groups
What is an experimental group?
The group that receives an experimental procedure. This group is exposed to changes in the independent variable being tested.
What is an independent variable?
the variable that is altered during a scientific experiment (controlled by the experimenter)
What is a hypothesis?
A proposed explanation for a phenomenon
What is a Controlled Group
A group separated from the rest of the experiment such that the independent variable being tested cannot influence the results.
What is a Procedure?
A clear description of how the experiment will be carried out
A controlled experiment may be used to determine whether or not plants need to be watered to live. The first group would be plants that are not watered. The second group would consist of plants that receive water. Which is the experimental group?
Second group, group that has watered plants
What is a dependent variable?
the variable that changes in response to the independent variable.
A hypothesis states a presumed relationship between two variables in a way that can be tested with data. It may take the form of a cause-effect statement ("if x,...then y" statement). Is X the independent or dependent variable?
Independent Variable
A controlled experiment may be used to determine whether or not plants need to be watered to live. The first group would be plants that are not watered. The second group would consist of plants that receive water. Which is the control group?
How should a procedure be set up?
A procedure should be easy to follow. It should have step-by-step directions for conducting the experiment. The directions may be numbered to be sure they are done in the correct order.
a scientist may wonder whether or not a species of bacteria needs oxygen in order to live. To test this, cultures of bacteria may be left in the air, while other cultures are placed in a sealed container of nitrogen (the most common component of air) or deoxygenated air (which likely contains extra carbon dioxide). Which is the experimental group?
Containers in the Nitrogen and containers in the deoxygenated air
Controlled variable (Constant)
A variable that is kept the same during a scientific experiment.
A hypothesis states a presumed relationship between two variables in a way that can be tested with data. It may take the form of a cause-effect statement ("if x,...then y" statement). Is Y the independent or dependent variable?
Dependent variable
Researchers who test anti-wrinkle facial products would follow a similar approach. They would recruit volunteers all within a specified age range of 38-45 and distribute bottles to all of the subjects. While the bottles would all appear to hold the same product, some people received bottles that do not have the compound that is intended to reduce wrinkles. What is the control group?
The people who received bottles that do not have the compound that is intended to reduce wrinkles are in the control group
Why do scientists write detailed procedures?
. A good procedure is so detailed and complete that it lets someone else duplicate your experiment exactly!
OR
It allows the scientist to conduct an experiment with a plan
Why do we use experimental groups?
To find the values of the independent variable and the impact on the dependent variable
In a study to determine whether how long a student sleeps affects test scores, one variable is the length of time spent sleeping while the other variable is the test score. Which variable is the independent variable and which is the dependent variable?
The independent variable is the length of time spent sleeping while the dependent variable is the test score.
Hypothesis: If you drink coffee before going to bed, then it will take longer to fall asleep. What is the independent variable and what is the dependent variable?
Drinking coffee before bed = Independent
Amount of time to fall asleep = Dependent
A scientist may wonder whether or not a species of bacteria needs oxygen in order to live. To test this, cultures of bacteria may be left in the air, while other cultures are placed in a sealed container of nitrogen (the most common component of air) or deoxygenated air (which likely contains extra carbon dioxide). Which container is the control?
Bacteria left in the air (normal conditions)
Fill in the blank: To guarantee a fair test when you are conducting your experiment, you need to make sure that the only thing you change is the ___________. And, all the controlled variables must remain constant.
True or False: An experiment can only contain one experimental group.
False, an experiment may include multiple experimental groups at one time
Why do we use controlled variables (constants in the experiment)?
A control variable in science experiments is what allows you to compare other things that may be contributing to a result because you have kept other important things the same across all of your subjects. For example, one control variable in the plant growth experiment could be temperature. You would not want to have one plant growing in green light with a temperature of 20°C while another plant grows in red light with a temperature of 27°C.
Hypothesis: If garlic repels fleas, then a dog that is given garlic every day will not get fleas. What are the independent and dependent variables?
Giving garlic to the dog = independent variable Whether fleas are repelled = dependent variable
Why do we use controlled groups?
Isolates the independent variable's effects on the experiment and can help rule out alternative explanations of the experimental results.
Fill in the blank. Every good experiment also compares different groups of trials with each other. Such a comparison helps insure that the changes you see when you change the independent variable are in fact caused by the independent variable. There are two types of trial groups _____________________
Experimental and Control Groups