Experimental Design and Implementation Honors Biology

Scientists are Investigators... All scientists, including biologists, have a certain way of investigating the world 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 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. 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 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 Testable hypothesis Controlled environment for both experimental group and control group Controlled environment for both experimental group and control group Test one independent variable, record the changes of one dependent variable Test one independent variable, record the changes of one dependent variable Multiple trials performed 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! Observations are the start of experimentation! Curiosity leads to hypothesis formation Curiosity leads to hypothesis formation HYPOTHESIS: If-then statement that will be tested through an experiment 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 experiment: Any experiment where the researcher places safeguards against error wherever possible Controlled experiments require many factors 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 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 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 Constants are factors that are identical between the control group and the experimental group Question: Why are constants important for each experiment? 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: 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 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 Good experimental design includes only TWO variables, or things that are changed during experimentation Independent Variable: What YOU as the scientist decide to change Independent Variable: What YOU as the scientist decide to change Dependent Variable: What is measured over the course of the experiment Dependent Variable: What is measured over the course of the experiment

Memory Aid: “I” choose the I.V. “I” choose the I.V. The dependent variable (D.V.) depends upon what I.V. is being tested The dependent variable (D.V.) depends upon what I.V. is being tested There is a cause and effect relationship between the two variables There is a cause and effect relationship between the two variables

Two Data Types We Can Collect QUALITATIVE DATA: descriptive data QUALITATIVE DATA: descriptive data Answers questions like: Answers questions like: How does it feel? How does it feel? What is going on? What is going on? What is it like? 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 Data will be collected and analyzed so that others may understand it Tables, charts, and graphs may be used 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 Graphs are labeled BELOW the graph!!!

Labeling Tables 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 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 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? 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.