BASIC CONCEPTS OF EXPERIMENTAL DESIGN

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BASIC CONCEPTSOF EXPERIMENTAL DESIGN
Science answers questions with experiments
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We will begin by asking a question about Hot
Solutions
What is a good question for our experiment?
How does adding more calcium chloride affect the
temperature of the water?
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Now we need a hypothesis to guide our
investigation.
What is a hypothesis?
Your best thinking about how the change you make
might affect another factor. Tentative
or trial solution to the question. An if
then statement.
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Now we will write a hypothesis for Hot Solutions
more scoops of calcium chloride are added to water
If .. , then
.. .
the temperature of the water will increase
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Variables
What are variables in an experiment?
Variables are things that change.
What are the variables in our Hot Solutions
experiment?

• Amount of calcium chloride
• Temperature of the water

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More about our variablesamount of calcium
chloride temperature of the water
The independent variable is the variable that is
purposely changed. It is the manipulated
variable. The dependent variable changes in
response to the independent variable. It is the
responding variable.
What is the Hot Solutions independent variable?
amount of calcium chloride
What is the dependent variable?
temperature of the water
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Another Look at Our Hypothesis
INDEPENDENT VARIABLE If more scoops of calcium
chloride are added to water, DEPENDENT
VARIABLE then the temperature of the water will
increase.
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Writing A Title for the Experiment
What should a title state?
The title should state The Effect of the
Independent Variable on the Dependent Variable.
What is a good title for Hot Solutions?
TITLE The Effect of Various Amounts of Calcium
Chloride on the Temperature of Water
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Levels of the Independent Variable
How many different levels (amounts) of calcium
chloride should we test?
3 ? 5? 10? The more the better?
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The Control in an Experiment
What is a control?
The part of the experiment that serves as the
standard of comparison.
Why is a control necessary?
It is the unchanged part of the experiment that
detects the effects of hidden variables.
What is a good control for Hot Solutions?
CONTROL No (zero) scoops of calcium chloride
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Constants in an Experiment
What are constants in an experiment?
Factors that are kept the same and not allowed to
change
What should be kept constant in Hot Solutions?
CONSTANTS Same amount of water Same time to
dissolve Constant stirring
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Repeated Trials
What are repeated trials?
The number of times that a level of the
independent variable is tested.
Why are repeated trials necessary?
They reduce the possibility of chance errors
affecting the results.
How many repeated trials are needed in Hot
Solutions? 2? 3?
4? The more the better?
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Experimental Design Diagram
Title Hypothesis IV DV C
Independent Variable Levels of IV
control of repeated trials Dependent
Variable Constants
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Experimental Design Diagram
Title The Effect of Various Amounts of Calcium
Chloride on the Temperature of Water

Hypothesis If more scoops of calcium
chloride are added to the water, then the
temperature of the water will increase. IV
Amount of calcium chloride (scoops) 0 scoops 2
scoops 4 scoops 6 scoops 8 scoops 10 scoops
(control) 3 trials 3 trials 3 trials
3 trials 3trials 3 trials DV
Temperature of water
C Same amount
of water (100 mL), Same time to dissolve (2min),
Constant stirring
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Generating Experimental Ideas
How do you select a topic for an experiment?
THE FOUR QUESTION STRATEGY
Q1 What materials are readily available for
conducting experiments on _(CaCl2)_ ?
Q2 How does _(CaCl2)_ act?
Q3 How can I change the set of _CaCl2)_
materials to affect the action?
Q4 How can I measure or describe the response
of _CaCl2)_ to the change?
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Constructing Data Tables
What should a data table communicate?
Relationship between the independent and
dependent variables
Order in which the independent variable is changed
Purpose of the experiment
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Sample Data Table
Title The Effect of Various Amounts of Calcium
Chloride on the Temperature of Water
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TEST YOUR UNDERSTANDING
What is wrong with this data table? Title Water
Temperature
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Constructing a Graph
What is the purpose of a graph?
Graphs communicate in pictorial form the data
collected in an experiment
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Bar vs. Line Graphs - Which Should I Use?
The type of graph to use depends on the type of
data collected.
Two kinds of data Discrete and Continuous
Discrete data are categorical like days of the
week, color, and brand of battery. Intervals
between the data have no meaning.
USE A BAR GRAPH
Continuous data are associated with measurements
involving a standard scale. Examples are amount
of fertilizer in grams and height of people in
centimeters. Intervals between data have meaning.
USE A LINE GRAPH
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Why was a bar graph used with this data?
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Why was a line graph used with this data?
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What kind of graph should we use for Hot
Solutions?
Bar
or
Line
Explain your answer.
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Step 1 Constructing a Graph DRAW AND LABEL
AXES
Temp. of Water (deg C)
Y Axis - Dependent Variable
Amount of Calcium Chloride (scoops)
X Axis - Independent Variable
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Step 2 Constructing a Graph WRITE DATA PAIRS
Experimental Data
Data Pairs (0, 0) (2, 4) (4, 7) (6, 10) (8,
14) (10, 17)
X
Y
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Step 3 Constructing a Graph - DETERMINE SCALES
FOR AXES
Increase values on axes by 1, 2 ,5, 10
or multiples of 10. There should be about 5
numbered subdivisions on each axis.
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X Largest value Smallest value Range
10 scoops - 0 scoops 10 scoops
10 scoops divided by 5 2 scoops
Average Temp. change (deg C)
10
Y Largest value Smallest value Range
17 deg C 0 deg. C 17 deg C 17 deg C
divided by 5 3.4 or 5 deg C
5
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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Step 4 Constructing a Graph PLOT DATA PAIRS
.
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Data Pairs (0, 0) (2, 4) (4, 7) (6, 10) (8,
14) (10, 17)
.
15
.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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Step 5 Constructing a Graph DRAW A
LINE-OF-BEST-FIT
.
20
.
15
.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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Step 6 Constructing a Graph TITLE THE GRAPH
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
20
.
15
.
The title should state the effect of the
independent variable on the dependent variable.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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Step 7 Constructing a Graph SUMMARIZE
TRENDS
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
20
.
As the amount of calcium chloride added to water
was increased, the temperature of the water also
increased.
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.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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TEST YOUR UNDERSTANDING Q1- What is wrong with
this graph?
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
20
.
15
.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
1
7
3
5
9
Amount of calcium chloride (scoops)
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TEST YOUR UNDERSTANDING Q2 - What is wrong with
this graph?
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
.
17
.
14
10
.
Average Temp. change (deg C)
.
7
4
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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TEST YOUR UNDERSTANDING Q3 - What is wrong with
this graph?
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
20
.
15
.
Average Temp. change
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride
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TEST YOUR UNDERSTANDING Q4 - What is wrong with
this graph?
.
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
10
8
.
Amount of Calcium Chloride (scoops)
6
.
4
.
.
2
0
0 5 10 15 20 25
Average Temp. Change (deg C)
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TEST YOUR UNDERSTANDING Q5 - What is wrong with
this graph?
THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
.
20
.
15
.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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TEST YOUR UNDERSTANDING Q6 - What is wrong with
this graph?
.
20
.
15
.
Average Temp. change (deg C)
10
.
.
5
.
0
0 2 4 6 8 10
Amount of calcium chloride (scoops)
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TEST YOUR UNDERSTANDING Q7 - What is wrong with
this graph?

THE EFFECT OF ADDING VARIOUS AMOUNTS OF CALCIUM
CHLORIDE ON THE TEMPERATURE OF WATER
40
30
.
Average Temp. change (deg C)
.
20
.
.
.
10
.
0
0 10 20 30 40 50
Amount of calcium chloride (scoops)
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BASIC CONCEPTS OF EXPERIMENTAL DESIGN Developed
By Harry Dillner Text Adapted From Science
Experiments and Projects for Students, 3rd ed.
Cothron, Giese and Rezba, Kendall-Hunt,
2000 Delaware Department of Education, Science
Van Project 655 Glenwood Avenue, Smyrna, DE
19977 Original Version September, 2000 - Latest
Revision October, 2001