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The scientific method (article) | Khan Academy
www.khanacademy.org/science/biology/intro-to-biology...How the scientific method is used to test a hypothesis. ... At the core of biology and other sciences lies a problem-solving approach called the scientific method. The scientific method has .... Sunderland, MA: Sinauer Associates, 2003. Raven ...
Subjects
y Intro to biology science of biology
The scientific method
How the scientific method is used to test a hypothesis.
Introduction
A
biology investigation usually starts with an observation—that is,
something that catches the biologist’s attention. For instance, a cancer
biologist might notice that a certain kind of cancer can't be treated
with chemotherapy and wonder why this is the case. A marine ecologist,
seeing that the coral reefs of her field sites are bleaching—turning
white—might set out to understand why.
How do biologists follow up on these observations? How can you follow up on your own observations of the natural world? In this article, we’ll walk through the scientific method, a logical problem-solving approach used by biologists and many other scientists.
The scientific method
At the core of biology and other sciences lies a problem-solving approach called the scientific method. The scientific method has five basic steps, plus one feedback step:
- Make an observation.
- Ask a question.
- Form a hypothesis, or testable explanation.
- Make a prediction based on the hypothesis.
- Test the prediction.
- Iterate: use the results to make new hypotheses or predictions.
The
scientific method is used in all sciences—including chemistry, physics,
geology, and psychology. The scientists in these fields ask different
questions and perform different tests. However, they use the same core
approach to find answers that are logical and supported by evidence.
Scientific method example: Failure to toast
Let's build some intuition for the scientific method by applying its steps to a practical problem from everyday life.
1. Make an observation.
Let's
suppose that you get two slices of bread, put them into the toaster,
and press the button. However, your bread does not toast.
- Observation: the toaster won't toast.
2. Ask a question.
Why didn't my bread get toasted?
- Question: Why won't my toaster toast?
3. Propose a hypothesis.
A hypothesis
is a potential answer to the question, one that can somehow be tested.
For example, our hypothesis in this case could be that the toast didn't
toast because the electrical outlet is broken.
- Hypothesis: Maybe the outlet is broken.
This
hypothesis is not necessarily the right explanation. Instead, it's a
possible explanation that we can test to see if it is likely correct, or
if we need to make a new hypothesis.
A
hypothesis must be testable and falsifiable in order to be valid. For
example, “Botticelli’s Birth of Venus is beautiful" is not a good
hypothesis, because there is no experiment that could test this
statement and show it to be false.
However, "People find Boticelli's Birth of Venus to be beautiful" is
falsifiable, because you could conduct an experiment in which you asked
many people from different walks of life whether they thought the
painting was beautiful. Notice that how we phrase a hypothesis can have a
big impact on whether it is valid or not.
This
question comes up a lot, particularly in reference to things like
Darwin's theory of evolution. A theory is different from a hypothesis,
though they're certainly related. A hypothesis is a potential answer to a
relatively small, specific question. A theory, on the other hand,
addresses a broader question and is supported by a large amount of data
from multiple sources1,2start superscript, 1, comma, 2, end superscript.
For
example, "The toaster won't toast because the electrical outlet is
broken" is a hypothesis, whereas "Electrical appliances need a source of
electricity in order to run" is closer to a theory.
4. Make predictions.
A
prediction is an outcome we'd expect to see if the hypothesis is
correct. In this case, we might predict that if the electrical outlet is
broken, then plugging the toaster into a different outlet should fix
the problem.
- Prediction: If I plug the toaster into a different outlet, then it will toast the bread.
5. Test the predictions.
To
test the hypothesis, we need to make an observation or perform an
experiment associated with the prediction. For instance, in this case,
we would plug the toaster into a different outlet and see if it toasts.
- Test of prediction: Plug the toaster into a different outlet and try again.
- If the toaster does toast, then the hypothesis is supported—likely correct.
- If the toaster doesn't toast, then the hypothesis is not supported—likely wrong.
The
results of a test may either support or contradict—oppose—a hypothesis.
Results that support a hypothesis can't conclusively prove that it's
correct, but they do mean it's likely to be correct. On the other hand,
if results contradict a hypothesis, that hypothesis is probably not
correct. Unless there was a flaw in the test—a possibility we should
always consider—a contradictory result means that we can discard the
hypothesis and look for a new one.
Why is it that we can't conclusively prove a hypothesis? And can we actually disprove a hypothesis?
One key distinction here is between what's logically possible and what's practically possible. Logically speaking, it's impossible to prove a hypothesis, but possible to disprove one. Practically speaking, it's challenging to either prove or disprove a hypothesis beyond the slightest doubt.
Logical possibility
As
an example, suppose we have the hypothesis that all apples are red, and
we test this hypothesis by examining a group of ten apples and seeing
what color they are. If all ten apples are red, our hypothesis is
supported, but it's not proven: if we looked at more apples, some of
them might turn out to be green. On the other hand, if one of our ten
apples is green, we have—in a world of perfect information and no
error—disproven our hypothesis.
Practical possibility
Practically
speaking—"in real life"—it's still impossible to prove a hypothesis
since it's not even logically possible to prove a hypothesis. However,
in real life scenarios, it also becomes difficult to disprove a
hypothesis beyond any imaginable doubt.
For example, suppose that we examine our apples in the scenario above and find that one of them is green. If the green apple is bona fide,
the hypothesis cannot be correct. However, it's possible that the apple
is not actually green, in the sense we care about, and that we
classified it as a green apple due to an error or a wrong assumption.
For example, perhaps the green apple is a decorative apple that someone
painted. Or maybe it's a red apple covered with green mold, which makes
it look green on first examination.
Building a body of evidence
In
a sense, we can never conclusively disprove the hypothesis that all
apples are red in the real world because we can't exclude the tiny
possibility of some kind of error, bad assumption, or bizarre
coincidence.
However,
suppose that we carefully investigate every alternative explanation we
can think of—painted apples, moldy apples, etc.—and don't find support
for any of them. In addition, let's say we repeat our experiment by
looking at a much larger number of apples, and we find a consistent
fraction of green ones. Additionally, people on neighboring farms report
that they routinely see green apples as well.
In
this case, although our hypothesis that all apples are red may not be
disproven beyond all imaginable doubt, it is so strongly contradicted as
to be effectively disproven. In other words, no one is likely to
consider it correct, design experiments around it, or base assumptions
on it.
Acknowledgements: The apple example of hypothesis testing comes from KA Guardian Andrew M.,
who used it in an explanation in the comments section of this article.
Many thanks to Andrew M. and other readers for their thoughtful
discussion of hypotheses, proof, and disproof, which led to the revision
and expansion of this section.
6. Iterate.
The last step of the scientific method is to reflect on our results and use them to guide our next steps.
And the result is:
Left panel: My bread toasts! Hypothesis is supported.
Right panel: My bread still won't toast. Hypothesis is not supported.
- Iteration time!
Left panel (in case of hypothesis being supported): But what is actually wrong with the outlet?
Right panel (in case of hypothesis not being supported): Hmm...maybe there is a broken wire in the toaster.
- If the hypothesis was supported, we might do additional tests to confirm it, or revise it to be more specific. For instance, we might investigate why the outlet is broken.
- If the hypothesis was not supported, we would come up with a new hypothesis. For instance, the next hypothesis might be that there's a broken wire in the toaster.
In most cases, the scientific method is an iterative
process. In other words, it's a cycle rather than a straight line. The
result of one go-round becomes feedback that improves the next round of
question asking.
How is the scientific method used by biologists?
This
article uses a practical example to show how the scientific method
works. However, you may be curious about how the scientific method is
used in actual biology research. If so, check out the next article!
Controlled experiments:
Learn how controlled experiments are used for hypothesis testing and
what the alternatives are if an experiment isn't possible. See an
example on coral bleaching!
Attribution
This article is a modified derivative of the following articles:
- "The science of biology," by OpenStax College, Biology (CC BY 4.0). Download the original article for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.4.
- "The process of science," by OpenStax College, Concepts of Biology (CC BY 4.0). Download the original article for free at http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.10.
The modified article is licensed under a CC BY-NC-SA 4.0 license.
Works cited
- "Definitions of fact, theory, and law in scientific work." National Center for Science Education. October 17, 2008. http://ncse.com/evolution/education/definitions-fact-theory-law-scientific-work.
"Science at multiple levels." Understanding cience. Accessed October 23, 2016. http://undsci.berkeley.edu/article/howscienceworks_19.9.
Additional references
"Definitions of fact, theory, and law in scientific work." National Center for Science Education. October 17, 2008. http://ncse.com/evolution/education/definitions-fact-theory-law-scientific-work.
Purves, W. K., D. E. Sadava, G. H. Orians, and H. C. Heller. "Biology is a science." In Life: The science of biology, 10-13. 7th ed. Sunderland, MA: Sinauer Associates, 2003.
Raven, P. H., G.B. Johnson, K. A. Mason, J. B. Losos, and S. R. Singer. "Science practice 3: Questioning scientifically." In Biology, 9. 10th ed. AP ed. New York, NY: McGraw-Hill, 2014.
Reece,
J. B., L. A. Urry, M. L. Cain, S. A. Wasserman, P. V. Minorsky, and R.
B. Jackson. "In studying nature, scientists make observations and form
and test hypotheses." In Campbell biology, 16-21. 10th ed. San Francisco, CA: Pearson, 2011.
"Science at multiple levels." Understanding Science. Accessed October 23, 2016. http://undsci.berkeley.edu/article/howscienceworks_19.
"What are independent and dependent variables?" National Center for Education Statistics. https://nces.ed.gov/nceskids/help/user_guide/graph/variables.asp.
Why can't a hypothesis be
definitively dis-proven? I understand why you can never conclusively
prove a hypothesis, but rather, just acquire more and more evidence for
it. But it seems, citing the example above, if one's hypothesis for a
car not starting is the vehicle is out of gas, and in fact the tank is
full of gas, then that hypothesis has been definitively dis-proven.
Edit 1: Note above in the lesson under heading 5. "Testing the predictions" it offers an explanation to "Why can't a… (readmoreof this comment)
Edit 1: Note above in the lesson under heading 5. "Testing the predictions" it offers an explanation to "Why can't a… (readmoreof this comment)
Hypotheses are more disprovable than
they are provable. If you get a piece of evidence that contradicts your
hypothesis, you can reject the hypothesis, barring experimental error
or incorrect assumptions about the system. The same wouldn't be true if
you got a piece of evidence that supported your hypothesis, because it
would remain possible that your hypothesis was not correct and you
simply needed to test it more thoroughly or with a larger sample.
The potential for experimental error and… (readmoreof this comment)
The potential for experimental error and… (readmoreof this comment)
If we observe and get no solution, what would be the point of scientific method?
The Scientific Method gives us an
orderly method to observe a phenomenon, formulate a question and a
hypothesis to answer the question, and a methodology to test the
hypothesis. After testing the hypothesis we discover if the hypothesis
is true or not, and if not true, then a new hypothesis can be formed and
tested with the ultimate goal of answering the original question. Most
often, the first hypothesis is found to NOT be correct, but the
experiment to test the hypothesis provides more data… (readmoreof this comment)
Is there anything called scientific fact?For example,the shape
of the earth is geo-spherical.Is there any scientist who would disagree
to that?Not every single scientist in the world would agree with the
theory of evolution.In the beginning,scientists thought big bang is just
a theory,but now it's an established scientific fact.What exactly is
the difference between a scientific fact and a scientific theory?
Of course there are facts, but it is
a mistake to compare them to theory as though a fact is "better" than a
theory. A fact is an observation that we make. A theory is a coherent
explanation of the facts. The word theory in science does not have the
meaning that it has when people use it in ordinary conversation to
suggest something tentative. That the earth is round is a fact (an
observation), not a theory (an explanation of the observed facts).
Gravity is theory. Atoms are a theory.… (readmoreof this comment)
a hypothesis is supported (likely correct), a theory has lots of
evidence to support it. What then Makes a theory become a LAW. Such as
the Law of Gravity? Only difference i see is a law has a mathematical
proof. Is this a correct assumption? or what Constitutes a law?
Theories don't become laws. Here is a good resource for defining how these scientific concepts relate: http://ncse.com/evolution/education/definitions-fact-theory-law-scientific-work
I just wanted to ask how can you use the scientific method to figure out the gravity and outer space?
This is a REALLY great question.
Ask "how does gravity work"
come up with a theory "it must have something to do with the earths orbit around the sun."
Design an experiment... There is a reason I am not going into astronomy... I don't know how you would test this... Except by finding out what the gravitational pull is from different planets in the solar system. Venus, which is almost the same size, and is close to the earth, still does not have the same, or near the same gravitational pull. So… (readmoreof this comment)
Ask "how does gravity work"
come up with a theory "it must have something to do with the earths orbit around the sun."
Design an experiment... There is a reason I am not going into astronomy... I don't know how you would test this... Except by finding out what the gravitational pull is from different planets in the solar system. Venus, which is almost the same size, and is close to the earth, still does not have the same, or near the same gravitational pull. So… (readmoreof this comment)
Is there a way to both prove and
disprove a hypothesis? Say....you had a hypothesis on....er.....the way
the world spins or something. You had proof.....and you also didn't (in
the terms that you read a book that supports your hypothesis, however,
your colleagues or something see what you think proves your hypothesis
actually doesn't, because they visualize or read a part in that book
differently.). So..............am I just making stuff up here or could
this be an actual situation/is proven\… (readmoreof this comment)
You're making stuff up :-) A statement is either true or it
is false. You can prove that a hypothesis is false by presenting counter
evidence, but you cannot prove that a hypothesis is true simply because
you have not heard of a counter example.
I thought a hypothesis was an "if, then" statement, and not a prediction?
Well, you could consider it to be both. If you say, "If I
do X then Y will happen" you are predicting what will happen if you do
something.
How is DNA created?
DNA is made of building blocks
called nucleotides. These building blocks are made of three parts: a
phosphate group, a sugar group and one of four types of nitrogen bases
(adenine, thymine, guanine, & cytosine). To form a strand of DNA,
nucleotides are linked into chains, with the phosphate and sugar groups
alternating. When DNA replicates, it separates into 2 strands and then
nitrogenous bases on the original strands code for the arrangement of
nucleotides in the new strands based on the… (readmoreof this comment)
This was an Intresting topic but how does the parasite enter the
frog does it eat its way through the skin or inject itself or what?
They probably enter through the mouth/gills or some opening.
If you can't really disapprove a hypothesis the why do teachers
always say you need more evidence? Is that not disapproving?
You can, and, if you become a
scientist, you should disprove a hypothesis or even theory. Because they
can be. You cannot however PROVE either of them. Every theory and
hypothesis is simply "not disproven" There is no such thing as a proven
anything in science. The scientific method is a process developed to
provide explanation for observable facts. Over time facts have become
more definable because of the method, i.e.: old question, "Why is the
sky blue?", new question, "Why does the… (readmoreof this comment)
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