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 Experiment1. 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

rage

Roo

t Num

ber

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.