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Experimental Design and Implementation
Honors Biology
Scientists are Investigators. . .
All scientists, including biologists, have a certain way of investigating the world
Scientific investigation involves gathering information about a specific topic in a reliable and repeatable manner
Let’s talk about it. . .
You have learned the scientific method for many years in school.
What do you already know about making an investigation reliable AND repeatable? List your ideas on your notes sheet. . .
What makes an experiment reliable and repeatable?
Testable hypothesis
Controlled environment for both experimental group and control group
Test one independent variable, record the changes of one dependent variable
Multiple trials performed
Many constants are set in place to improve validity of data
Researcher eliminates bias whenever possible
Procedure is repeatable with similar results
Observations make us wonder
Observations are the start of experimentation!
Curiosity leads to hypothesis formation
HYPOTHESIS: If-then statement that will be tested through an experiment
What is a good hypothesis for this study?
A scientist tests an idea on two groups of pigeons. She releases the pigeons in Group 1 and records the direction of their flight. The pigeons in Group 2 are given a substance that blocks their sense of smell for a short time. The scientist then releases them and records the direction of their flight. Her data are shown on the diagram below.
The test of a hypothesis must be CONTROLLED
Controlled experiment: Any experiment where the researcher places safeguards against error wherever possible
Controlled experiments require many factors
Components of a Controlled Experiment
1. Experimental Group AND Control Group
2. Many constants
3. One Independent Variable
4. One Dependent Variable
Setting Up Your Groups. . .
Experimental Group: The group that receives the experimental treatment
Control Group: The group that is IDENTICAL to the experimental group in every way, except it does not receive the experimental treatment
QUESTION: Why do we always use a control group in an experiment?
Let’s Practice!
Identify the control group and experimental group in this experiment:
A scientist tests an idea on two groups of pigeons. She releases the pigeons in Group 1 and records the direction of their flight. The pigeons in Group 2 are given a substance that blocks their sense of smell for a short time. The scientist then releases them and records the direction of their flight.
Constants. . .
Constants are factors that are identical between the control group and the experimental group
Question: Why are constants important for each experiment?
Constants Help Eliminate Bias
Bias: Any preconceived ideas or judgement calls that are used to draw conclusions INSTEAD of conclusions drawn from experimentation
BIAS IS BAD! As scientists, we draw conclusions from data, not opinions and personal feelings
What constants should be in place in this experiment?
A scientist tests an idea on two groups of pigeons. She releases the pigeons in Group 1 and records the direction of their flight. The pigeons in Group 2 are given a substance that blocks their sense of smell for a short time. The scientist then releases them and records the direction of their flight.
Variables
Good experimental design includes only TWO variables, or things that are changed during experimentation
Independent Variable: What YOU as the scientist decide to change
Dependent Variable: What is measured over the course of the experiment
Memory Aid:
“I” choose the I.V.
The dependent variable (D.V.) depends upon what I.V. is being tested
There is a cause and effect relationship between the two variables
Two Data Types We Can Collect
QUALITATIVE DATA:
descriptive data
Answers questions like: How does it
feel? What is going
on? What is it like?
QUANTITATIVE DATA:
numerical data
Answers questions like: How much? How often? How many?
Identify the I.V. and D.V. in this experiment. . .
A scientist tests an idea on two groups of pigeons. She releases the pigeons in Group 1 and records the direction of their flight. The pigeons in Group 2 are given a substance that blocks their sense of smell for a short time. The scientist then releases them and records the direction of their flight.
Once you perform the experiment. . .
Data will be collected and analyzed so that others may understand it
Tables, charts, and graphs may be used
Ask yourself: Is my data verifiable? Is my data reliable?
If you say NO to either of these questions, your design was POOR
Labeling Graphs
FIGURE 1. Average Root Number by Treatment
0 1000 2000 3000 4000 5000 6000 7000 80000
400
800
1200
1600
2000
Peat Mix Vermiculite
Hormone Concentration (ppm)
Ave
rag
e R
oo
t Nu
mb
er
Graphs are labeled BELOW the graph!!!
Labeling Tables
Media Average # Roots/Cutting Hormone Treatment (ppm)Peat 70.5 0
390.5 1000920.5 30001141 8000
Media Average # Roots/Cutting Hormone TreatmentMixed 159 0
406.5 1000665.5 3000904.5 8000
Media Average # Roots/Cutting Hormone TreatmentVermiculite 770.5 0
1551.5 10001590.5 30001861 8000
TABLE 1. Average Root Number by Treatment
Remember: Tables are labeled at the TOP!!!
Validity and Reliability
A valid conclusion for an experiment is one that can be backed up by many trials with similar data
Reliable data is information gathered many times by many scientists running the exact same procedure
Let’s Go Back . . .
What could our scientist do to make her conclusion reliable AND her data valid?
A scientist tests an idea on two groups of pigeons. She releases the pigeons in Group 1 and records the direction of their flight. The pigeons in Group 2 are given a substance that blocks their sense of smell for a short time. The scientist then releases them and records the direction of their flight.