Chapter 1

Introduction to the Scientific Method
Can Science Cure the Common Cold?


1.1 The Process of Science

§ “Science is a body of knowledge and the process used to obtain the knowledge”

§ As knowledge, science is simply an array of facts and explanations of those facts.

§ The processes to obtain information in science is called the scientific method:

§ Observing

§ Proposing ideas

§ Testing

§ Discarding those ideas that fail


The Nature of Hypotheses

§ Hypothesis: proposed explanation

§ Testable - must be able to make observations and measurements to evaluate the hypothesis

§ Falsifiable - the observations or measurements must potentially be able to proven the hypothesis false


The Nature of Hypotheses

§ Where do hypotheses come from?

§ Both logical and creative influences are used

§ Figure 1.1


Scientific Theory

§ Powerful, broad explanation of a large set of observations

§ Can explain some aspect of nature, for example

§ Rests on many hypotheses that have been tested

§ Generates additional hypotheses


The Logic of Hypothesis Tests

§ Example:  consuming vitamin C decreases the risk of catching a cold

§ Inductive reasoning: combining a series of specific observations into a generalization

§ Jamie took vitamin C and did not get a cold

§ Jesse took vitamin C and did not get a cold

§ Jordan took vitamin C and did not get a cold

§ Conclude: People with names starting with “J” that took vitamin C did not get a cold


§ To test, make a prediction using deductive reasoning.

§ Can be constructed similarly to an “if…then” statement

§ IF people who took vitamin C did not get a cold…

§ THEN the people who take vitamin C will not get a cold


§ The process looks something like this:

§ Figure 1.3


§ 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.  A different explanation might be better.


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.

§ Figure 1.4


The Experimental Method

§ Experiments are contrived situations.

§ Variables: factors that can change in value under different conditions

§ Independent variables can be manipulated by the scientist (dosage of vitamin C to subjects in an experiment)

§ Dependent variables cannot be changed by the researcher (susceptibility to colds by subjects in an experiment)

§ Controlled variables are kept the same for all subjects (try to make sure nobody starts the experiment with a cold)


Controlled Experiments

§ Controlled experiment: tests the effect of a single variable

§ Control: a subject who is not exposed to the experimental treatment

§ Differences can be attributed to the experimental treatment.

§ Controls and controlled variables are not the same thing.


§ 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 (placebo).

§ Both groups rated the effectiveness of their treatment on relieving cold symptoms.


§ In one experiment, people who received echinacea tea felt that it was 33% more effective at reducing symptoms.

§ Figure 1.7


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 blinding: the person administering the treatments also doesn’t know until after the experiment is over

§ gold standard” for experimentation


Using Correlation to Test Hypotheses

§ It is not always possible or ethical to experiment on humans.

§ Using existing data, is there a correlation between variables?

§ A correlation is simply a relationship between two 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.

§ Figure 1.10


§ Caution!  Correlation does not imply causation.

§ The correlation might be due to other reasons.

§ A cause is something that actually leads to an effect; it’s not always easy to see what causes something to happen!


Using Correlation to Test Hypotheses

§ Figure 1.11


1.3  Understanding Statistics

Overview: What Statistical Tests Can Tell Us

§ We can extend the results from small samples to an entire population.

§ Find out if there is a difference between two samples: Is it real or due to chance?


The Problem of Sampling Error

§ Sampling error: the effect of chance

§ We can calculate the probability that a result is simply due to sampling error.

§ Statistically significant: an observed difference is probably not due to sampling error


§ Standard error: the statistical variability in the data used to calculate the mean (average).

§ Much population variation = large standard error (more spread-out results/data)

§ Small population variation = small standard error (less spread-out results/data)


Factors that Influence Statistical Significance

§ Sample size

§ The true difference between populations

§ Bigger is better: more likely to detect differences


The Problem of Sampling Error

§ Figure 1.14


What Statistical Tests Cannot Tell Us

§ If an experiment was designed and carried out properly

§ Can evaluate the probability of sampling error, not observer error

§ May not be of any biological significance


1.4 Evaluating Scientific Information

Primary Sources

§ Researchers can submit a paper about their results to a professional journal (primary source).

§ Peer review: evaluation of submitted papers by other experts

§ Secondary sources include those sources such as books, news reports, the internet, and advertisements, which may provide some of the information contained in a primary source


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

§ 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 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.


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