Scientific Method:
Experimental Design and
Laboratory Report Writing
Available online @
http://www.redwood.org/stewart
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Experimental Organizer
Data
Laboratory Report
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Observe the world around you!
Consider:
Prior experience
Initial testing
RESEARCH
EXAMPLE:
After studying about recycling, members of John’s biology class investigated the effect of various
recycled products on plant growth. John’s lab group compared the effect of different aged grass
compost on bean plants. Because decomposition is necessary for release of nutrients, the group
hypothesized that older grass compost would produce taller bean plants. Three flats of bean
plants (25 plants/flat) were grown for 5 days. The plants were then fertilized as follows: (a) Flat
A: 450 g of 3-month-old compost, (b) Flat B: 450 g of 6-month-old compost, and (c) Flat C: 0 g
compost. The plants received the same amount of sunlight and water each day. At the end of 30
days the group recorded the height of the plants (cm), and plant health was described.
Choose topic
Experimental Organizer
Data
Laboratory Report
Experimental Organizer
 To get you started,
organize your ideas
into an
Experimental
Organizer.
Eventually, you will
use this to write
your complete
Laboratory Report.
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Experimental Organizer
Data
Title
 The effect of IV on DV.
QuickTime™ and a
decompressor
are needed to see this picture.
EXAMPLE:
The Effect of Different Aged Compost on
Bean Plant Growth.
Laboratory Report
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Experimental Organizer
Data
Hypothesis
 If IV then DV.
 Be specific.
QuickTime™ and a
decompressor
are needed to see this picture.
EXAMPLE:
If older compost is applied, then plant
height will be taller
Laboratory Report
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Experimental Organizer
Data
Laboratory Report
Independent Variable (IV)
 What will be
purposefully changed
by the experimenter.
What you are testing.
There is only ONE IV in
a controlled
experiment!
EXAMPLE:
Age of Compost
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Experimental Organizer
Data
Laboratory Report
Levels (Treatments) of IV
 Specific changes that
will be made to the IV.
 One is the control: The
standard for comparing
experimental effects.
EXAMPLE:
Levels of I.V.
(2 or more plus the control,
which must be identified)
3 month
old
compost
6 month
old
compost
No
Compost
(control)
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Experimental Organizer
Data
Number of Trials
 Number of replications
of each
level/treatment.
 At least 2 trials per
level/treatment.
EXAMPLE:
Num b e r o f t r ia ls y o u will co n d u ct f o r ea ch
I.V. lev el
25
p lants
25
p lants
25
p lants
Laboratory Report
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Experimental Organizer
Data
Laboratory Report
Dependent Variable (DV)
 Variable that “depends” on the
IV. Your RESULTS.
 Specifically:
 Quantitative Measurements:
NUMBERS (Quantities)
 Qualitative Measurements:
CHARACTERISTICS (Qualities)
EXAMPLE:
Quantitative Measurements: Height of plants (cm)
Qualitative Measurements: Plant Health description
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Experimental Organizer
Data
Constants
 Procedures and materials
used throughout
experiment to assure
there is only one
Independent Variable.
EXAMPLE:
Amount of light, amount of water,
amount of compost
Laboratory Report
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Experimental Organizer
Data
Laboratory Report
Looking ahead: Use the Experimental
Organizer to--among other things-- write
your PROCEDURES in the EXPERIMENTAL
DESIGN section of your Laboratory Report.
 The Experimental Organizer
will help describe your
experimental PROCEDURES
in detail. Include:
 MATERIALS
 STATE IV, DV,
CONSTANTS, ETC.
 SET-UP PROCEDURES
 DATA COLLECTION
PROCEDURES
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Experimental Organizer
Data
Laboratory Report
Data Tables
1. Make a table containing vertical columns for (1) the independent variable,
(2) dependent variable and (3) statistical calculations (i.e. mean). Use a ruler. *
are the cells of your table large enough?
2. Subdivide the column for the dependent variable to reflect the number of
trials.
3. Under the I.V. column, list the levels (treatments) of the independent
variable in rows – preferably from the smallest to the largest.
4. Title the data table (The Effect of I.V. on. D.V.)
5. Record all data values and calculations in the appropriate locations!
EXAMPLE:
Age of Compost
(months)
Height of Plants at 30 Days
(cm)
Trials
1
0 months (con trol)
3 months
6 months
2
3
4
etc.
Mean Pl ant
Height (cm)
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Experimental Organizer
Data
Laboratory Report
Graphs
 Use Data Tables to
The Effects of the Amount of Compost on the Height of Bean Plants
30.0
create Graphs




1.Identify dependant (y-axis) and independent (xaxis) variables (Y depends on X)
the dependant variable is the variable you are
measuring
the independent variable is the variable you are testing or the one that you are changing
2. Establish/calculate a scale for each axis
what is the range for the data?
how accurate do you need to be?
what are my graph paper limitations (if any)?
3.Bar (DISCONTINUOUS data) or Line Graph
(CONTINUOUS data)?
4.Label the x-axis and y-axis (designate units in
parenthesis)
5.Title the graph: The Effect of Independent Variable
on Dependent Variable (*same as data tables!)
25.0
20.0
Height of Plants (cm)

15.0
Mean Plant Height
10.0
5.0
0.0
0.0 g
10.0 g
20.0 g
30.0 g
Amount of Compost (grams)
40.0 g
50.0 g
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Experimental Organizer
Data
Laboratory Report
Graphs
The Effect of the Am ount of Com post on the Ove rall Health of Bean Plants
 Use Data
0.9
Tables to
create
Graphs
QUALITATIVE
DATA:
 Frequency of
MODE, or
 Frequency of one or
more of the
dependent variables
0.7
0.6
Frequency Distribution
 FOR
0.8
0.5
UN = Unhealthy
H = Healthy
0.4
0.3
0.2
0.1
0
0.0 g
10.0 g
20.0 g
30.0 g
Amount of Compost (grams)
40.0 g
50.0 g
Choose topic
Experimental Organizer
Data
Laboratory Report
Use your Experimental Organizer
and other information to write a
full Laboratory Report which
includes:
 A. TITLE
 B. INTRODUCTION
 C. HYPOTHESIS
 D. EXPERIMENTAL DESIGN
 E. DATA
 F. DISCUSSION
 G. CONCLUSION
 H. REFERENCES CITED
Laboratory Report
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Experimental Organizer
Data
A. Title
 Use Title from Experimental
Organizer.
Laboratory Report
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Experimental Organizer
Data
Laboratory Report
B. Introduction
Conduct further research and write a
complete Introduction. Stating:
 BACKGROUND: WHAT
 RATIONALE, PURPOSE:
WHY do this experiment
 explain HYPOTHESIS: HOW
you expect it will turn out
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Experimental Organizer
Data
C. Hypothesis
 Use Hypothesis from
Experimental Organizer.
Laboratory Report
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Experimental Organizer
Data
Laboratory Report
D. Experimental Design
 Using Experimental Organizer
as a start, describe your
experimental PROCEDURES
in detail. Include:
 MATERIALS
 STATE IV, DV,
CONSTANTS, ETC.
 SET-UP PROCEDURES
 DATA COLLECTION
PROCEDURES
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Experimental Organizer
Data
Laboratory Report
E. Data
 Include Data Tables and Graphs
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Experimental Organizer
Data
F. Discussion
 Discuss data in detail: WHAT
happened.
 Identify trends and
anomalies.
 Explain WHY you got the
results you did.
 Compare findings with other
research/results.
 Suggest HOW to improve,
further the study.
Laboratory Report
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Experimental Organizer
Data
G. Conclusion
 Restate purpose,
summarize results in
relation to Hypothesis.
Laboratory Report
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Experimental Organizer
Data
Laboratory Report
H. References Cited
 List sources used.