1.1 The Process of Science
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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
© 2013 Pearson Education, Inc.
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.
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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.