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The scientific method

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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:
  1. Make an observation.
  2. Ask a question.
  3. Form a hypothesis, or testable explanation.
  4. Make a prediction based on the hypothesis.
  5. Test the prediction.
  6. 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.
  1. Observation: the toaster won't toast.

2. Ask a question.

Why didn't my bread get toasted?
  1. 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.
  1. 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.

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.
  1. 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.
  1. 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.

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.
  1. 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.

Want to join the conversation?

  • duskpin ultimate style avatar for user Monae P.
    I thought a hypothesis was an "if, then" statement, and not a prediction?
    (168 votes)
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  • piceratops seedling style avatar for user John C Schermerhorn
    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?
    (60 votes)
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  • marcimus purple style avatar for user C.C.Guan
    If you can't really disapprove a hypothesis the why do teachers always say you need more evidence? Is that not disapproving?
    (46 votes)
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  • aqualine sapling style avatar for user Midnight crow
    What if one time an experiment works and the next it does not?
    (29 votes)
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    • winston default style avatar for user Emily Fung
      Exactly, like others said if you do more experiments, then you will be sure to find out which info is credible. When I did experiments, my teacher asked us to write a summary about the results we got, so I tested out our hypothesis 3 times to find the average out of all of them, and I got pretty good info out of my experiment. I hope this helps you out!
      (27 votes)
  • female robot ada style avatar for user sushi
    I've been told that the proper way to compose a hypothesis is by using an if/then statement. But in the example above, it doesn't use an if/then statement. My question is, is there a proper way to write a hypothesis? If so, what is it? Thanks in advance:)
    (22 votes)
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    • blobby purple style avatar for user eunbee
      I think that there is no definite format to writing a hypothesis, but as you said, yes there is a 'proper' and appropriate way to writing a hypothesis.

      Like the article says, a hypothesis must be testable, meaning we can do experiments with it to see if it is supported or not. I think usually non-testable hypothesis are something that are not exactly 'measurable' or 'observable', such as "Many people may think that red apples are attractive". There is no accurate way of measuring if people think that red apples are attractive.

      Yes, an if/then statement is a very safe way to write a hypothesis. One of the things that we must be careful when writing a hypothesis is that we should not make it a conclusion (an actual 'statement'!); for instance, "Red apples cause pimples." is a conclusion that could be obtained from an experiment, while "Red apples may cause pimples" might be a hypothesis.
      However, yes the best way is to write an if/then statement, because it is formatting your prediction in a very testable way. You are saying 'IF I do this..' - which is the experimental portion- that 'THEN this will happen'- which is the prediction or 'educated guess' portion.
      (26 votes)
  • purple pi purple style avatar for user Nicholas Song
    I am using a new account now, so I’ll ready my question.
    I was looking at the last step, iteration. At my school, they have taught us an extra step, which would be conclusion and analyze/share data. Could someone specify the definition of the conclusion and analyze/share data? I get the analyze/share data part, but I always get stuck on conclusions, especially so when I have to write lab reports.
    (12 votes)
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    • winston baby style avatar for user Ivana - Science trainee
      Why do you think you get stuck at conclusions? Are you afraid to say what you mean? Have you ever taken Logic classes?

      I haven't but after quite a year it became habitual and 'easy' to conclude.

      Maybe you lack the theoretical part or you are just scared of those lab reports (my personal opinion but I may be wrong).

      Do not be afraid, and keep practicing.

      If you read dozens of Scientific articles you may get an idea of what 'Conclusions' look like. Also, analyze and share means what it says. Analyze the best way you can do (don't be too hard on yourself) and share with others (peers, professors, online, scicomm, etc).


      Good luck :D and keep asking questions :D
      (6 votes)
  • blobby green style avatar for user shawn.lawhun
    i thought a hypotheis was a educated gusse
    (11 votes)
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  • duskpin seedling style avatar for user Khareema Taylor
    What's the dependent and independent variables, the constants, and the controls?
    (5 votes)
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    • winston baby style avatar for user Ivana - Science trainee
      Dependent variable is the one which relies on the independent variable. It relies on other variables. Meaning if you change other things this one will change as well.

      independent variable is variable which can change regardless of the experiment.

      Control is a group in an experiment which must be conducted an used to compare with the experimental group. You cannot test your hypothesis if you do not have a control group. What you get from the experimental group is meaningless if not compared to the control group.
      (14 votes)
  • blobby green style avatar for user Ger Thornton
    I don't understand What are the independent and dependent variables in an experiment?
    I have watched the videos and read the articles but still do not understand. Can someone please explain what they are in a practical way. Thanks :-)
    (7 votes)
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    • male robot hal style avatar for user Andrew M
      Another (I think better) word for the independent variable is the manipulated variable. It's the variable that the experimenter directly manipulates in order to see what happens,.

      The dependent variable can also be called the responding variable. It's the one where we watch it to see what happens when we make changes to the manipulated variable.
      (5 votes)
  • duskpin sapling style avatar for user asmaa2003
    how many times do you have to do a hypothesis to get the right solution for your problem?
    (4 votes)
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