In This Lesson:
Scientific Method
(Lesson 2 of 4)
Today is Thursday,
September 3rd, 2015
Pre-Class:
What’s a characteristic of a good
experiment? (lots of answers here)
Put your Checks Lab in the Turn-In Box.
Today’s Agenda
• Some Inspiration
• Scientific Method Terminology Defined
• The Checks Lab
• Where is this in my book?
– P. 10-11
By the end of this lesson…
• You should be able to use the scientific
method to make decisions and analyze results.
• You should be able to determine the roles of
various treatment groups in creating a
thorough experiment.
Some Inspiration
• “I never failed once. It just happened to be a
2000 step process.”
– Thomas Edison, in reference to his many “failed”
attempts to invent the modern electric light bulb.
• No one ever learns to walk without falling first.
• Basically, I want you to know that I put no
pressure on you to be right every time. I’m not
grading you on what you say – I’m just trying to
help you learn.
The Scientific Method
• The scientific method can be presented in many
or few steps.
• Here’s our general one for this class:
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Observe [a problem or pattern]
Research [the background info, if any]
Hypothesize [your best guess for an explanation]
Experiment [test your hypothesis]
Analyze [make sure you’re seeing a true pattern]
Conclude [accept or reject your hypothesis, explain]
Exploring the Steps
• Observe
– Being observant is crucial for being a scientist.
– You are born with some basic tools for observing.
– Scientists have developed
other tools for observation
too.
http://thebeautybrains.com/wp-content/uploads/2006/12/senses.jpg
Testing Observation Skills
• The Checks Lab!
Exploring the Steps
• Research
– All science is built on previous science.
– Finding background information allows you to
learn more about the pattern you are seeing.
Exploring the Steps
• Hypothesize
– Develop your best guess as to what could explain
the pattern.
– Generally “if-then” statements.
– Consider all evidence you have researched or
observed.
– Ensure that your hypothesis is testable!
• “falsifiable”
• What is not a testable hypothesis?
Testable Hypotheses
• Discuss with your partner which of the
following hypotheses are testable by an
experiment:
– A: Spiders given caffeine make asymmetrical webs.
– B: God created all life.
– C: There are no unicorns.
– D: Eye color is a trait inherited from one’s parents.
About Choice C…
• If I were to go to the forest around here and
not see a woodpecker, can I say it’s not there?
– No, I can only say I don’t have any evidence that
it’s there.
• The same goes for hypotheses.
– It’s more about saying, “Yes, we have evidence,”
or “no, we don’t,” than about “right” and “wrong.”
Null Hypothesis
• In any experiment, there is always a second
hypothesis – the null hypothesis.
• The null hypothesis is that there is no difference.
– For the apple-ripening experiment, it would mean
that apples ripen equally fast in oxygen and carbon
dioxide.
• Your experiment is performed to determine
whether you can reject the null hypothesis and
conclude that there is a significant difference.
• No significant difference means you must accept
the null hypothesis.
Experiment
• Test your hypothesis.
• Features of a good experiment:
– High sample size (n).
• In other words, they tested a lot of subjects.
– Has a control group and variable groups.
• An un-modified sample and a sample being tested.
– Only one variable tested at a time.
• Sources of error are minimized.
– Can be repeated by others.
• Procedure is clear.
Example Experiment
• Hypothesis:
– Spiders given caffeine build asymmetrical webs.
• Experiment:
– Gather 100 spiders of same species.
• High sample size, no additional variables.
– Give 50 spiders caffeine and water, give other 50 plain
water.
• Control group (plain water) and variable group (caffeine and
water).
– Record procedure clearly.
• Repeatability.
Why Control Groups?
• Why did we need to have a group of spiders
given just water? Weren’t we testing just
caffeine?
• Was this a web from a normal spider or a
caffeine spider?
http://www.trinity.edu/jdunn/spiderdrugs.htm
Control Group
• The control group is there to be the “normal”
result.
• It’s the “standard” to which we compare other
results.
– Without a control, we don’t truly know what
normal is.
• To identify the control group, simply find the
test subjects that are not given any special
treatment.
Controls and Constants
• By the way, don’t forget that controls are
different from constants.
– Constants are things kept the same in an
experiment. Sometimes constants are referred to
as “controlled variables.”
• Example: All spiders used in the experiment were the
same species.
– Controls are the test subjects treated “normally.”
• Example: Spiders not given any kind of “treatment” like
caffeine.
Spiders on Drugs
• Scientists actually did this test.
– NASA scientists!
• Here’s what they found:
– Normal spiderweb:
Spiders on Drugs
• Caffeine:
• Mescaline/peyote:
Spiders on Drugs
• Marijuana:
• Benzedrine/Speed:
Spiders on Drugs
• Sleeping Pills:
The first one?
• LSD
Why do we need a control group?
• Another reason we need a control group is
because of the placebo effect.
• Basically, the placebo effect states that if you give
patients a pill (even one that does nothing), but
tell them it works, the patient frequently will
achieve better health (or at least perceive it).
• In other words, “thinking” you’re getting better
can actually make you feel better!
– It works with pills, (fake) surgery, and even just telling
people they’re getting better.
The Placebo Effect
• To get around the placebo effect, doctors give
patients…a placebo!
• A placebo, sometimes called a sugar pill, is a
pill designed to look like medication but
actually do nothing.
– The term “placebo” can be used for other things
that do nothing but look like they might, as well.
• More on the placebo effect: TED – Eric Mead
What’s a variable group?
• The variable group is where you test your
hypothesis.
– In the spider example, it’s the caffeinated spiders.
• You compare the variable group to the control
group.
– Example: Comparing the webs of caffeinated
spiders to the “control” (normal diet) spiders.
One last bit on variables…
• There’s actually two kinds of variables out
there – dependent variables and independent
variables.
• Dependent variables (sometimes called
responding variables) are those that are
measured in the experiment.
– Example: Spider web shape.
One last bit on variables…
• Independent variables are those changed by
the experimenter. Typically there’s a general
category of independent variables, and
they’re often the treatments.
– Example: Substances given to the spiders.
• BIG HINT: The independent variable group is
sometimes called the treatment group or the
experimental group.
– What’s being treated in the experiment? The
independent variable.
Analyze Your Data
• You need to make sure your data are different
from chance.
– Do enough spiders given caffeine make weirdo
webs?
– What if some of the caffeine spiders just aren’t
good at making webs to begin with, caffeine or
not?
Analyze Your Data
• You know how the word “bomb” is not really a
problem most of the time, but if you say it on
an airplane, suddenly it’s a big deal?
• Science has one of these words:
– Significant.
• “Significant” means something has been
statistically proven to be so.
“Significant” is Significant
• Example: “Apples stored in pure carbon
dioxide ripened significantly faster than those
stored in pure oxygen.”
– This is only acceptable if an experiment was
performed and data analyzed proving that this is
the case. If you haven’t done that, but notice a
pattern, consider:
• “Apples stored in pure carbon dioxide ripened
noticeably faster than those stored in pure
oxygen.”
Draw Your Conclusion
• Your conclusion is the grand end result of
everything you’ve done and all the evidence
you’ve found.
• Your conclusion may support your hypothesis
or it may not, it doesn’t matter.
• What does matter is that your conclusion is
supported by your data.
After the Scientific Method
• When a group of experiments all seem to be
confirming the same pattern, that pattern may
be considered a theory.
• A theory is a well-tested explanation that
explains a wide range of observations.
– Basically, a concept that proves a lot of
hypotheses.
• A theory is not an unproven statement or
something scientists just “think” is the case.
Theory Examples
• Can you think of any theories that exist?
– Quantum Theory
– Theory of Evolution
– Theory of Gravity
Reasoning
• There are two ways to “reason” according to
science:
– Deductive reasoning
– Inductive reasoning
• Neither one is necessarily correct, but they are
both different.
Deductive Reasoning
• Think of it as “big-to-small” reasoning:
• Example:
– All humans are mortal
– Justin Bieber is human
– Therefore, Justin Bieber is mortal
http://www.socialresearchmethods.net/kb/dedind.php
Inductive Reasoning
• “Small to big” reasoning:
• Example:
– Beyoncé lip-synced
– Beyoncé is a pop singer
– Therefore, other pop singers lip sync
Deductive or Inductive?
• I like cheese.
• Pizza has cheese.
• I will like pizza.
• This is an example of inductive reasoning.
– I start with a specific statement (I like cheese – a
component of a larger dish) and move to a general
statement that I will like pizza.
– Maybe I don’t like tomato sauce. That could be a
dealbreaker. But we don’t know that yet…
Deductive or Inductive?
• I can ice skate.
• Hockey involves ice skating.
• Therefore, I will be good at ice hockey.
• This is also inductive.
– I am able to do a small component of a larger
picture.
Labeling the Experiment
• Francisco Redi was one of the first to prove
that maggots don’t come from rotting meat.
• He used three jars: one open, one covered
with netting, and one sealed.
• Into each he placed bits of meat and let it rot.
• His hypothesis was that maggots come from
flies.
– Notice that this is a testable hypothesis.
Labeling the Experiment
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•
•
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What’s his control?
What’s his independent variable?
What’s his dependent variable?
What are the constants?
Jar 1:
Flies
Jar 2:
http://faculty.sdmiramar.edu/dtrubovitz/micro/history/Redi.html
No flies
Jar 3:
No flies
Answers
• Control
– Meat in the open jar (Jar 1).
• Independent Variable
– Jar coverings.
• Dependent Variable
– Maggots/flies.
• Constants
– Same jars, same meat, same location.
Labeling the Experiment
• A biologist thinks that exercising is good for mice.
• He takes 20 two-week-old mice and gives them all identical cages
and identical diets, and he keeps them in the same room.
• 10 mice also receive an exercise wheel. The other 10 receive an
exercise wheel that does not spin.
• He records their life spans and compares.
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What is the hypothesis?
What is the sample size?
What are the constants?
What is the control (or control group)?
What is the variable (or variable group)?
What’s the independent variable?
What’s the dependent variable?
Could anything have been done better?
Answers
• Hypothesis
– Mice that exercise live longer.
• Sample Size
– 10 (20 total mice, but in two groups of 10).
• Constants
– Same age, same room, same cage, same exercise wheels.
• Control
– Mice with a non-spinny wheel.
• Variable/Treatment Group
– Mice with a spinny wheel.
• Independent Variable
– Exercise or no exercise.
• Dependent Variable
– Life span.
• Improvements
– Same litter of mice, bigger sample size.
Simpsons Scientific Method
• Visit Quia.com/web
• Log-in:
– Username: [firstnamelastname]832
– Password: Gleicher[house/apt #]
• Go to the class web page.
• Look for Simpsons Scientific Method and take
the quiz.
Closure: Bad Science?
• Bad Science:
– TED: Ben Goldacre – Battling Bad Science
• Publication Bias:
– TED: Ben Goldacre – What Doctors Do Not Know
About the Drugs They Prescribe
• Science Denial:
– TED: Michael Specter – The Danger of Science
Denial