Scientific methodpowerpoint

Copyright © 2009 Pearson Education, Inc.
© 2013 Pearson Education, Inc.
PowerPoint Lecture prepared by
Jill Feinstein
Richland Community College
Fourth Edition
BIOLOGYScience for Life | with Physiology
Colleen Belk • Virginia Borden Maier
ChapterChapter 11
Can Science Cure the Common Cold?
Introduction to the Scientific Method
* Components of this PowerPoint were altered by Lissa Walls to better fit
the learning objectives of Integrated Science: The Living World (SCI 106)
*

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 is important to learn about the process of science
called the scientific method.
 The scientific method is used to solve problems
and answer questions.
 Observations
 Proposing ideas
 Testing ideas
 Discarding or modifying ideas based on results

The Nature of Hypotheses
 Hypothesis: proposed explanation for a set of
observations
 Scientific Hypotheses need to be:
 Testable –possible to examine the hypothesis through
observations
 Falsifiable –able to be
proven false if it is untrue
 Objective – not influenced by personal feelings or
opinions
 Ethical - moral

Where do hypotheses come from?
 Both logical and creative influences are used to
develop a hypothesis

Scientific Theory
 Powerful, broad explanation of a large set of
observations
 Based on well supported hypotheses
 Supported by research from several different
independent sources

Steps of the Scientific
Method
 The process looks
something like this:

The Logic of Hypothesis Tests
 A hypothesis that fails our test is rejected and
considered disproven.
 A hypothesis that passes is supported, but not
proven.
 Why not? An alternative hypothesis might be
the real explanation.

1.2 Hypothesis Testing
The Experimental Method
 Experiments are designed 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
 Standardized variables (aka controlled
variables) kept constant so that any difference in
outcome is due ONLY to treatment

Controlled Experiments
 Controlled experiment: tests the effect of a
single variable
 Control: a subject (or group) who is not exposed
to the experimental treatment but has all other
variables the same
 Given either no treatment or a placebo

 Differences seen between the experimental
group and control group can be attributed to
the experimental treatment
 Random Assignment
 An effective way of assigning individuals to
groups for testing

 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 rated the effectiveness of their
treatment on relieving cold symptoms

 People who received
echinacea tea felt that
it was 33% more effective
at reducing symptoms

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 do not 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

Minimizing Bias in Experimental Design

 The “gold standard” for experimentation
 Double-blind, placebo controlled, and randomized
experiments
 Model systems can be used in experiments
when it appears too dangerous or unethical to test
on humans
 examples: mice, rats, dogs and pigs
 A correlation can be used to test hypotheses
when controlled experiments on humans are
impossible to perform

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?

 Results of such a study: the number of colds
increases as stress levels increase
 Caution! Correlation does not imply causation!!

 The correlation might be due to other reasons

1.3 Understanding Statistics
Overview: What Statistical Tests Can Tell Us
 Data collected during experimentation should be
organized and analyzed using statistical methods
 Comparing means (averages) is a common way to
compare the data from two groups
 Statistical tests will tell us if differences between
groups are due to treatment or due to chance
 Statistically significant: unlikely the observed
difference is due to chance IF experiment was
designed and carried out properly
 AKA there is a true difference between the two
groups/items compared

The Problem of Error
 During experimentation researchers need to minimize error;
errors affect the outcome of experiments
 Experimental error: inconsistent or incorrect
measurements, poorly functioning equipment, timing errors,
confusing instructions to subjects, etc.
 Sampling error: estimation error because of surveying a
sample of the population rather than the whole population
 Sample size: the number of units (people, plants,
animals, illnesses) to be tested/surveyed in an
experiment
 A larger sample size is more true of the population from
which the sample was taken

What Statistical Tests Cannot Tell Us
 If an experiment was designed and carried out
properly
 If observer error occurred; statistical tests can only
evaluate the probability of sampling error
 Practical or biological significance of results

1.4 Evaluating Scientific Information
Primary Sources
 Researchers can submit a paper about their
experimental methods and 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

Information from Anecdotes
 Anecdotal evidence is based on one person’s
experience, not on experimental data
 Example: a testimonial from a celebrity

Science in the News

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

Understanding Science from Secondary Sources
 Use your understanding of the scientific method to
evaluate findings stated by secondary sources
 News media generally highlight only those science
stories that seem newsworthy
 They are more likely to report a positive result than
a negative one

1.5 Is There a Cure for the Common Cold?
 No, but prevention methods are known
 Wash your hands!
 No effect on cold susceptibility:
 Vitamin C
 Exposure to cold temperatures
 Exercise
 No vaccine for the common cold

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