Scientific Method
Scientific Analysis of Data
Steps in the Scientific method: ** given an experiment, be able to identify each
step
The steps of the scientific method are to:
Each experiment must have an independent variable, dependent variable and a
control.
*** Each experiment can have ONLY ONE INDEPENDENT VARIABLE tested at at
time.
Independent variable: what YOU change in an experiment (X-axis).
Dependent variable: what YOU MEASURE in an experiment (Y-axis).
An experimental group is the group in a scientific experiment where the
experimental procedure is performed. This group is exposed to the
independent variable being tested and the changes observed and recorded.
control group is a group separated from the rest of the experiment where
the independent variable being tested cannot influence the results. This
isolates the independent variable's effects on the experiment and can help
rule out alternate explanations of the experimental results.
Control: a condition where the result stays the same
Example of an experiment:
A scientist wants to test if a high protein diet will help fish spawn more; he feeds
100 fish with the high protein food and 100 fish with regular fish food with no high
protein. He finds that on average the experimental group lays about 43 eggs/day
and fish fed regular food lays about 10 eggs /day.
hypothesis: more fish will spawn if given high protein fish food.
Control group- no high protein fish food;
experimental group = a high protein diet;
result = experimental group lays about 43 eggs/day; fish fed regular food lays
about 10 eggs /day.;
conclusion = fish fed with high protein diet spawn more;
inference (not actually shown in the data, but a guess as to the reason for the
conclusion) =
the protein must increase egg production
example questions:
Sponge Bob wants to know if a special cream he has made will help build
muscles. So he asks 10 clams to smear the special cream on their muscles and 10
clams smear on mayonnaise on their muscles. Each day he measures how many
peanuts they can lift. He finds those with the cream can lift an average of 5
peanuts and those without the cream can lift 4 peanuts.
1. control? mayonnaise
2. independent variable? cream or no cream
3. dependent variable? number of peanuts they can lift
4. conclusion? cream does not give an advantage
Practice questions for experiments (http://www.quia.com/quiz/1015088.html)
Equipment used in scientific experiments:
*** given an experiment, be able to identify the equipment that is needed
1. beaker - a liquid-measuring container
2. test tube - used as holder of small amount of solution
3. graduated cylinder - measures approximate volume of liquids
4. graduated pipette - measures solution volumes
5. thermometer - measures temperature
6. balance - measures mass of material
7. pH meter - measures acidity of solutions
8. centrifuge - separates materials of varying density
9. pipette - used to transfer measured substances into another vessel
10. droppers - for addition of liquids, drop by drop
11. volumetric flasks - to measure precise volumes of liquid or to make
precise dilutions.
12. Spring scale – measures the force of weight of an object
13. Copier – to make large number of copies for surveys
14. Ruler – measure distance and length
15. Science journals and encyclopedias – to do research or to find info on a topic
16. Fossil records/ historical documents- to do research on genealogy,
pedigrees, paleontology, evolution
17. Checklists and identification keys- to identify specimens of organisms
18. Magnifying glass- very low magnification; used to view large objects
more closely; ** ex: leaf vein
19. Dissecting microscope or stereoscope- gives a 3-D image; low
magnification and resolution
** cannot see individual cells
20. Compound light microscope- high magnification ; low resolution- can see
cells; also can see larger organelles in the cell such as nucleus.
21. Electron microscope- high magnification and high resolution; can see
parts inside the cell
cost to effect ratio: the ratio of how much was spend in making the
machine/experiment and how many folks did it benefit.
example: if we spend 20 dollars and it helps 100 people, then what is the C:E ratio?
it is 20:100 =1:5
how to avoid bias in an experiment?
1. must have a control
2. use a large group
3. have other scientists repeat it.
precision- how close are several measurements taken by the same person.
accuracy- if we compare our measurement what it should be, how close is it?
** given numbers, be able to say how precise / accurate was the experiment
how to design a new machine1. research
2. plan/build a model or prototype
3. test it
4. publish results
Practice questions:
1. in the late 1800's, C.Eijkman studied a disease called beriberi, which is caused by
a vitamin deficiency. A disease similar to beriberi occurred in chickens that were
fed polished rice, which is rice that has had the bran layer removed. Chickens that
ate unpolished rice did not get the disease.
Eijkman convinced officials of a prison experiencing an outbreak of the disease to
start feeding the prisoners unpolished rice. The rate of beriberi decreased
dramatically. Which procedure would best convince other scientists who
questioned the results?
a. feed prisoners chicken b. provide the same number of prisoners polished rice
as with unpolished rice c. study other types of animal with beriberi d. compare
chickens that ate polished rice to those who ate unpolished rice
2. to look at the wings of butterflies, the best equipment to use is:
a. triple beam balance and microscope b. hand lens and triple beam balance
c. catch net and hand lens d. microscope and graduated cylinder
3. a researcher shows his results for some eyedrops. He showed over a two year
period, that the eyedrops did prevent lens from drying out. Before publishing his
results, to be sure it is free of bias, he should:
a. extend his research for three more years b. investigate similar products
c. test a larger population of subjects
perform the same experiment
d. have an independent research company
4. an inventor has an idea for a pest control product for farms. He proceeds to
build and marker the product. which step has he failed to do?
a. identify the need b. define the problem c. narrow the research d. test the
product
5. The length of a desk is 2 ft. Susan three measurements of the desk was: 4.6,
4.8, 4.7
Her results are:
a. accurate but not precise b. not accurate but precise c. accurate and precise
d. not accurate and not precise
answers: b. c. d. d. b.
Example 2
How the Scientific Method Works
by William Harris
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Harris, William. "How the Scientific Method Works" 14 January 2008. HowStuffWorks.com.
<http://science.howstuffworks.com/innovation/scientific-experiments/scientific-method.htm> 09
August 2011.
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Inside this Article
1. Introduction to How the Scientific Method Works
2. Scientific Method Definition
3. Scientific Method Parts
4.
5.
6.
7.
History of the Scientific Method
Cell Theory
Pasteur's Experiment
See more »
7. Scientific Method Steps
8. More Scientific Method Steps
9. Scientific Method Applications
10. Importance of the Scientific Method
11. Limitations of the Scientific Method
12. Lots More Information
13. See all Scientific Experiments articles
Scientific Method Steps
As more proof that there is no one way to "do" science, different sources describe the steps of the
scientific method in different ways. Some list three steps, some four and some five.
Fundamentally, however, they incorporate the same concepts and principles.
Image courtesy William Harris
For our purposes, we're going to say that there are five key steps in the method.
Step 1: Make an observation
Almost all scientific inquiry begins with an observation that piques curiosity or raises a question.
For example, when Charles Darwin (1809-1882) visited the Galapagos Islands (located in the
Pacific Ocean, 950 kilometers west of Ecuador), he observed several species of finches, each
uniquely adapted to a very specific habitat. In particular, the beaks of the finches were quite
variable and seemed to play important roles in how the birds obtained food. These birds
captivated Darwin. He wanted to understand the forces that allowed so many different varieties
of finch to coexist successfully in such a small geographic area. His observations caused him to
wonder, and his wonderment led him to ask a question that could be tested.
Step 2: Ask a question
The purpose of the question is to narrow the focus of the inquiry, to identify the problem in
specific terms. The question Darwin might have asked after seeing so many different finches was
something like this: What caused the diversification of finches on the Galapagos Islands?
Here are some other scientific questions:
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


What causes the roots of a plant to grow downward and the stem to grow upward?
What brand of mouthwash kills the most germs?
Which car body shape reduces air resistance most effectively?
What causes coral bleaching?
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Does green tea reduce the effects of oxidation?
What type of building material absorbs the most sound?
Coming up with scientific questions isn't difficult and doesn't require training as a scientist. If
you've ever been curious about something, if you've ever wanted to know what caused something
to happen, then you've probably already asked a question that could launch a scientific
investigation.
Step 3: Formulate a hypothesis
The great thing about a question is that it yearns for an answer, and the next step in the scientific
method is to suggest a possible answer in the form of a hypothesis. A hypothesis is often defined
as an educated guess because it is almost always informed by what you already know about a
topic. For example, if you wanted to study the air-resistance problem stated above, you might
already have an intuitive sense that a car shaped like a bird would reduce air resistance more
effectively than a car shaped like a box. You could use that intuition to help formulate your
hypothesis.
Generally, a hypothesis is stated as an "if … then" statement. In making such a statement,
scientists engage in deductive reasoning, which is the opposite of inductive reasoning.
Deduction requires movement in logic from the general to the specific. Here's an example: If a
car's body profile is related to the amount of air resistance it produces (general statement), then a
car designed like the body of a bird will be more aerodynamic and reduce air resistance more
than a car designed like a box (specific statement).
Notice that there are two important qualities about a hypothesis expressed as an "if … then"
statement. First, it is testable; an experiment could be set up to test the validity of the statement.
Second, it is falsifiable; an experiment could be devised that might reveal that such an idea is not
true. If these two qualities are not met, then the question being asked cannot be addressed using
the scientific method.
Let's say I have a problem: My car won't start. How would I use the scientific method to
solve this problem?
Scientific Method In Action
The Strange Case of BeriBeri
In 1887 a strange nerve disease attacked the people in the Dutch East Indies. The disease was beriberi.
Symptoms of the disease included weakness and loss of appetite, victims often died of heart failure.
Scientists thought the disease might be caused by bacteria. They injected chickens with bacteria from the
blood of patients with beriberi. The injected chickens became sick. However, so did a group of chickens
that were not injected with bacteria.
One of the scientists, Dr. Eijkman, noticed something. Before the experiment, all the chickens
had eaten whole-grain rice, but during the experiment, the chickens were fed polished rice. Dr.
Eijkman researched this interesting case. he found that polished rice lacked thiamine, a vitamin
necessary for good health.
1. State the Problem
2. What was the hypothesis?
3. How was the hypothesis tested?
4. Should the hypothesis be supported or rejected based on the experiment?
5. What should be the new hypothesis?
How Penicillin Was Discovered
In 1928, Sir Alexander Fleming was studying Staphylococcus bacteria growing in culture dishes. He
noticed that a mold called Penicillium was also growing in some of the dishes. A clear area existed
around the mold because all the bacteria that had grown in this area had died. In the culture dishes
without the mold, no clear areas were present.
Fleming hypothesized that the mold must be producing a chemical that killed the bacteria. He decided to
isolate this substance and test it to see if it would kill bacteria. Fleming transferred the mold to a nutrient
broth solution. This solution contained all the materials the mold needed to grow. After the mold grew, he
removed it from the nutruient broth. Fleming then added the nutrient broth in which the mold had grown to
a culture of bacteria. He observed that the bacteria died.
6. Identify the problem.
7. What was Fleming's hypothesis?
8. How was the hypothesis tested?
9. Should the hypothesis be supported or rejected based on the experiment?
10. This experiment lead to the development of what major medical advancement?