Science:
How to Do it Right
A Research in Ecology Primer
Scientific Reasoning:
Seeing Patterns
Radiation: Does it Harm Us?
 In the 1920s, Hermann Muller discovered that x-rays
caused mutations in fruit flies.
Radiation: Does it Harm Us?
 A mutation is a change in an organism’s DNA, and
it sometimes has physical consequences.
A mutagen is anything that increases the occurrence
of mutations.
Radiation: Does it Harm Us?
 Muller also discovered that xrays can change the DNA of
humans, causing defects.
 Other researchers noted that xrays, gamma rays and other
ionizing radiation caused
mutations in various species.
 Since then it has been shown
with many experiments that
ionizing radiation is a mutagen.
Inductive Reasoning
 Scientists who studied radiation noticed again and
again that ionizing radiation caused mutations.
 With many repeated, consistent observations, they
were able to make the general conclusion that
IONIZING RADIATION IS A MUTAGEN.
 Scientists who used these many
observations
to make a
conclusion were using
INDUCTIVE REASONING
Inductive Reasoning
Hypothesis
 A scientific hypothesis is
a tentative explanation-based on previous
knowledge--for an
observation.
 It’s an “educated guess”
that must be tested
experimentally.
 It is the starting point of
scientific inquiry.
Theory
 A scientific theory is a wellsubstantiated explanation
of some aspect of the
natural world.
 It can incorporate facts, laws,
inferences, and tested
hypotheses.
 A theory that has been
rigorously tested and confirmed
can be used to explain and
predict natural phenomena.
 In science, a “theory” is not a
vague idea about an observation.
Law
 A scientific law generalizes
a body of observations.
 At the time it is made, no
exceptions have been found to
the law.
 Scientific laws explain, but
they do not describe or tell us
why things happen.
 Example: Law of Gravity
 The Law predicts what will
happen to a dropped object,
but doesn’t’ explain why it
happens.
Scientists are Skeptics!
 skep·tic - ˈskeptik
(noun)
1. A person inclined to question
or doubt accepted opinions.
Critical thinking means
questioning things and
insisting on EVIDENCE.
Inductive Reasoning
 THEORY developed through specific, individual
observations via experimentation:
Once you have a theory…
…it can be used to predict
natural phenomena.
Deductive Reasoning
A Cautionary Tale:
 A theory alone is not enough to
explain every observation.
 Careful confirmation must be
done, and a good scientist never
assumes anything
 Because when you ASSUME,
you can make an ASS out of U
and ME.
August 6, 1945
 The United States dropped atomic bombs on
Hiroshima and Nagasaki, Japan
 Hiroshima was burned to ashes.
 Survivors suffered a living hell.
The Aftermath:
Radiation Injuries
 Epilation
 Hemorrhage
 Cataracts
 Leukemias and
other Cancers
Deductive Reasoning
: Ionizing radiation has been shown
experimentally to be a TERATOGEN.
 A teratogen is an agent that causes birth defects.
: Ionizing radiation contamination in
Hiroshima and Nagasaki will cause birth defects in
children born to survivors.
: What experiment could you
design to test this hypothesis?
Experimental Design
 In 1948, the Atomic Bomb Casualty Commission
(ABCC) began a six year study to monitor birth
defects in Hiroshima and Nagasaki.
 A total of 76,626 newborns were examined by ABCC
physicians.
 At the start of the study, women who were 20
weeks pregnant or more were made exempt from
food rationing, but had to register for this privilege.
 More than 90% of all pregnancies were thus
registered, and their outcomes recorded.
Experimental Results
 You’ll sometimes see horrific pictures of malformed
babies born after Hiroshima and Nagasaki.
 But were these abnormal babies caused by the
radiation?
 Fewer than 1% of the babies born during this
period showed signs of birth defects.
 Statistical testing revealed that this rate of birth
defects was not significantly different from that
occurring in areas without radiation contamination.
Let’s watch a movie.
https://www.youtube.com/watch?v=Iw2R7y65nFg
A Leap of Logic?
 THEORY:
 “Ionizing radiation promotes birth defects.”
 OBSERVATION:
 “This rabbit, which was born near an area in Japan
contaminated by radiation, has a birth defect.”
 CONCLUSION:
 “This rabbit’s birth defect was caused by ionizing
radiation.”
Did we skip a step or two?
Only the Facts.
 Multiple hypotheses make good
science!
 What are some other possible
hypotheses about the reason the bunny
has no ears?
The Strong Hypothesis
 A scientific hypothesis cannot be
proven correct.
 Piling up evidence to support a
hypothesis does not address the fact
that there may be a contradiction lying
in wait!
The Strong Hypothesis
The Strong Hypothesis
The Strong Hypothesis
The Strong Hypothesis
 The most powerful hypothesis
is one that can withstand
attempts to FALSIFY it
 (i.e., prove it wrong)
The Scientific Method
 OBSERVATION
 HYPOTHESIS (as many as are logical!)





EXPERIMENTAL DESIGN
PREDICTION
DATA COLLECTION
DATA ANALYSIS
CONCLUSION
The Scientific Method
 OBSERVATION:
A natural phenomenon poses a problem or
question.
The Scientific Method
 HYPOTHESIS - The investigator poses the question
in such a way that it can be tested by rigorously
designed experiments or field observations.
 Null hypothesis - Stated in terms of "no difference
between observed results and expected results" of an
experiment. Abbreviated Ho.
 Alternative hypothesis - The opposite of the null, and
actually the statement of interest. Abbreviated Ha.
The Scientific Method
 EXPERIMENTAL DESIGN- carefully designed to
yield data to either support or refute the hypothesis.
 Large enough sample size
 Exclusion of confounding factors
 Statistical tests
The Scientific Method
 PREDICTION- A statement about the expected results
of an experiment.
 DATA COLLECTION- The experiments are run, and
data are collected.
 DATA ANALYSIS- The data are subjected to rigorous
analysis via quantification and/or statistical tests to
determine whether any deviation from the expected
result is truly meaningful, or merely due to chance.
 CONCLUSION- The investigator accepts or rejects the
null hypothesis.
The Reward
 Good science is about
finding truth and
getting the facts.
 Knowing the cause,
might we some day
find a cure?