Transcript 1.1 The Process of Science

Chapter 1
Can Science Cure the Common Cold?
Introduction to the Scientific Method
Fourth Edition
BIOLOGY
Science for Life | with Physiology
Colleen Belk • Virginia Borden Maier
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Copyright © 2009 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
1.1 The Process of Science
 Science refers to a body of knowledge
 Science is not a giant collection of facts to be
memorized.
 It important to learn about the process of science
called the scientific method.
 The scientific method allows the solving of
problems and answering of questions
 done by:
 making observations
 proposing ideas in the form of hypotheses
 testing these ideas through experimentation
 discarding or modifying ideas based on results
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1.1 The Process of Science
The Nature of Hypotheses
 Hypothesis: proposed explanation for one or more
observations
 essentially a guess on “how things work”
 Mom says – “wear a hat or you will get a cold”
 her hypothesis is based on her theory that being chilled
will increased your chances of getting a cold
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1.1 The Process of Science
Where did Mom get this hypothesis from?
 both logical and creative influences are used to
develop a hypothesis
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The Nature of Hypotheses
 a hypothesis needs to be:
 Testable – you have to be able to examine the
hypothesis through observations
 the observations must have a material nature and must be
measureable
 some hypotheses are not testable and are therefore not
proper hypothesis
 e.g. get a cold because of a disturbance in psychic
energy
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The Nature of Hypotheses
 a hypothesis needs to be:
 Falsifiable – the hypothesis must be able to
potentially be proven false
 in science incorrect ideas must be discarded
 e.g. being chilled will give you a cold
 we can imagine a situation where this is not true
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1.1 The Process of Science
Ulcers and Bacteria
 long held belief that foods can cause ulcers

e.g. spicy food upsets your stomach through increased acid production 
ulcers
 based on standard medical practice for ulcers

drugs that lower stomach acid levels
 1982 – Australian scientists Robin Warren and Barry Marshall

found a specific strain of bacteria in tissue samples taken from ulcers

formulated a new hypothesis  Ulcers caused by this bacteria
 series of well-controlled studies using the bacteria Helicobacter pylori
 their hypothesis was testable and falsifiable

end result of their studies? Hypothesis was not rejected
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1.1 The Process of Science
Ulcers and Bacteria
 today this hypothesis is accepted by the scientific
community
 their work was rigorous and well-controlled and
reviewed by many other scientists with knowledge
in the field
 ALSO – no well-controlled studies examining a link
between spicy foods and ulcers have been
published
 so no alternative hypothesis has been proven
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1.1 The Process of Science
Scientific Theory
 Marshall and Berry based their hypothesis on previous
scientific knowledge
 called the germ theory of disease
 the germ theory of disease is an example of a Scientific
Theory
 Powerful, broad explanation of a large set of observations
 Based on well supported hypotheses
 Supported by research from several different
independent sources
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1.1 The Process of Science
What is a Theory?
 common meaning = untested hypothesis based on little
information
 in science = theory is a well-supported idea on how the
natural world works
 based on previous observations
 Marshall and Berry based their theory that bacteria cause
ulcers and their hypothesis that H. pylori causes human
stomach ulcers on the germ theory started by Louis
Pasteur
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1.1 The Process of Science
The Logic of Hypothesis Tests
 Inductive reasoning: combining a series of specific
observations into a generalization to create a hypothesis
 Hypothesis: You can prevent a cold by taking vitamin C
 this hypothesis was created through inductive
reasoning
 based on some well-known facts:
 1. fruits and veggies contain vitamin C
 2. people with diets rich in fruits and veggies are healthier
 3. vitamin C in an anti-inflammatory and can reduce nose and
throat irritation
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1.1 The Process of Science
The Logic of Hypothesis Tests
 To test the hypothesis you use deductive
reasoning:
 involves using a general principle to predict
an expected observation using if/then statements
 essentially you make a prediction
 e.g. - If vitamin C decreases the risk of catching a
cold, then people who take in additional Vitamin C
will get less colds.
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1.1 The Process of Science
The Logic of
Hypothesis Tests
 The process looks
something like this:
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1.1 The Process of Science
 So – HOW WOULD YOU GO ABOUT TESTING
YOUR PREDICTION????
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1.1 The Process of Science
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1.1 The Process of Science
The Logic of Hypothesis Tests
 A hypothesis that fails our test is rejected and
considered disproven.
 NOT ONE PUBLISHED STUDY ON VITAMIN C SHOWS
IT CAN PREVENT COLDS!!!
 A hypothesis that passes is supported  but not
proven
 Why not? An alternative hypothesis might be
the real explanation.
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1.2 Hypothesis Testing
 The most powerful way to test hypotheses: do
experiments
 Experiments support the hypothesis that the
common cold is caused by a virus.
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1.2 Hypothesis Testing
The Experimental Method
 Experiments are designed to collect data or
information to test specific hypotheses.
 Variables: factors that can change in value under
different conditions
 Independent variables can be manipulated by
the scientist
 Dependent variables cannot be changed by
the researcher
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1.2 Hypothesis Testing
Controlled Experiments
 Controlled experiment: tests the effect of a
single variable
 Control: a subject who is not exposed to the
experimental treatment but has all other variables
the same
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1.2 Hypothesis Testing
Controlled Experiments
 HYPOTHESIS: Compound “X” can make cells
grow faster
 EXPERIMENT: take cells and expose them to
Compound “X”
 GROUP #1: cells grown in the lab for 14 days in a
media containing Compound X
 GROUP #2: same cells grown in the same lab for 14
days in the same media NOT containing Compound X
 count the cells from the two groups and compare
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1.2 Hypothesis Testing
Controlled Experiments
 Differences seen between the experimental
group and control group can be attributed to
the experimental treatment.
Compound X
No Compound X
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Animation: Science as a Process: Arriving at Scientific Insights
Click “Go to Animation” / Click “Play”
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1.2 Hypothesis Testing
Controlled Experiments
 Example: Echinacea tea experiment:
 Hypothesis: drinking Echinacea tea relieves
cold symptoms
 Experimental group drinks Echinacea tea 5-6
times daily.
 Control group drinks “sham” Echinacea tea 5-6
times daily (placebo).
 Both groups rate the effectiveness of their
treatment on relieving cold symptoms.
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1.2 Hypothesis Testing
Controlled Experiments
 People who received
echinacea tea felt that
it was 33% more effective
at reducing symptoms.
 can you say that echinacea tea
prevents colds?
 NO!!!!!
 Why?
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1.2 Hypothesis Testing
Controlled Experiments
 Problems with this study
 1. People in the study
 sample size
 sample composition
 2. Data collection
 e.g. surveys and subjectivity
 3. Bias
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Minimizing Bias in
Experimental Design
 If human subjects know
whether they have
received the real
treatment or a placebo,
they may be biased.
 Blind experiment:
subjects don’t know what
kind of treatment they
have received
 Double blind
experiment: the person
administering the
treatments and the
subjects do not know
who is in each group
until after the experiment
is over
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1.2 Hypothesis Testing
Using Correlation to Test Hypotheses
 The “gold standard” for experimentation
 Double-blind, placebo controlled and randomized
experiments in humans
 A correlation can be used to test hypotheses
when controlled experiments on humans is
impossible to perform
 Model systems can be used in experiments
when it appears to dangerous or unethical to test
on humans
 examples: mice, rats, dogs and pigs
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1.2 Hypothesis Testing
Using Correlation to Test Hypotheses
 Using existing data, is there a correlation
between variables?
 Hypothesis: stress makes people more
susceptible to catching a cold
 Is there a correlation between stress and the
number of colds people have caught?
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1.2 Hypothesis Testing
Using Correlation to Test Hypotheses
 Results of such a study: the number of colds
increases as stress levels increase.
 Caution! Correlation does not imply causation.
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1.2 Hypothesis Testing
Using Correlation to Test Hypotheses
 The correlation might be due to other reasons.
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1.2 Hypothesis Testing
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1.3 Understanding Statistics
Overview: What Statistical Tests Can Tell Us
 Statistics in science is used to evaluate and
compare data.
 We can extend the results from small samples to an
entire population using statistical tests.
 Statistically significant: results of difference
between groups is due to random chance and not
an error in experimenting
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1.3 Understanding Statistics
The Problem of Sampling
Error
 Sampling error: the effect of
chance on experimental data
 we can calculate the
probability that a result is
simply due to sampling error.
 Confidence interval: the
range of values from a sample
that has a 95% probability of
containing the true population
mean (average)
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1.3 Understanding Statistics
Factors that Influence Statistical Significance
 Sample size
 The true difference between populations
 Bigger is better: more likely to detect differences
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1.3 Understanding Statistics
What Statistical Tests Cannot Tell Us
 If an experiment was designed and carried out
properly
 If observer error occurred, only can evaluate the
probability of sampling error
 May not be of any biological significance
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1.4 Evaluating Scientific Information
Sources
 Researchers can submit a paper about
their results to a professional journal
(primary source).
 Primary Sources undergo peer review:
evaluation of submitted papers by other
experts
 Secondary sources: books, news
reports, the internet, and advertisements
 Anecdotal evidence is based on one
person’s experience, not on
experimental data.

Example: a testimonial from a celebrity
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1.4 Evaluating Scientific Information
Science in the News
 Secondary sources may be missing critical information or
report the information incorrectly.
 Consider the source of media reports.
 Be careful with the internet since anyone can
post information.
 Be very cautious about claims made in paid advertisements.
Use your understanding of the process of science to evaluate
science stories.
 News media generally highlight only those science stories that
seem newsworthy.
 They are more likely to report a positive result than a negative
one.
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1.5 Is There a Cure for the Common Cold?
 No vaccine for the common cold
 No cure
 but prevention methods are known.
 #1 preventive measure - Wash your hands!
 the media gives us poor information
 no proven effect on cold susceptibility:
 increased Vitamin C intake
 exposure to cold temperatures
 exercise
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A(n) ________ is a proposed explanation for a
single observation.

scientific method

hypothesis

scientific theory

experiment
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A(n) ________ is a proposed explanation for a
single observation.

scientific method

hypothesis

scientific theory

experiment
© 2013 Pearson Education, Inc.
Which of the following is a scientific hypothesis?

Jazz is better music than rap.

Garden fairies make tomatoes grow better.

Hunting species to extinction is wrong.

Increasing the amount of protein in a cow’s
diet increases her milk yield.
© 2013 Pearson Education, Inc.
Which of the following is a scientific hypothesis?

Jazz is better music than rap.

Garden fairies make tomatoes grow better.

Hunting species to extinction is wrong.

Increasing the amount of protein in a cow’s
diet increases her milk yield.
© 2013 Pearson Education, Inc.
Which of the following is correct?

A hypothesis can be wrong.

A hypothesis is not always testable.

A hypothesis can prove a person’s values.

A hypothesis should be formed before making
any observations.
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Which of the following is correct?

A hypothesis can be wrong.

A hypothesis is not always testable.

A hypothesis can prove a person’s values.

A hypothesis should be formed before making
any observations.
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A statistical test evaluates the chance of _______.

observer error.

sampling error.

alternative mechanisms.

need for controls.
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A statistical test evaluates the chance of _______.

observer error.

sampling error.

alternative mechanisms.

need for controls.
© 2013 Pearson Education, Inc.