Evaluating examples of faulty scientific thinking. How to design and conduct a manipulative experiment.

1. Applying Scientific Thinking:
Suzy Housewife and Joe Texas
Dr. Mark A. McGinley
Professor, Head of Science Unit
Core Curriculum and General Education Office
Lingnan University

2. Scenario
• Children in the USA receive the MMR vaccine (which vaccinates them
from the measles, mumps, and rubella) at the age of 4. As a good
mother, Suzy Housewife, takes her son to be vaccinated on his 4th
birthday. Four months later her son is diagnosed with autism. Ms.
Housewife concludes that the vaccine caused her son to develop
autism and has since refused to have any more of her children
vaccinated and has encouraged all of her friends not to vaccinate
their children either.

3. Problems with Mrs. Housewife’s Scientific
Thinking
• As you discussed in class, there are a number of problems with Mrs.
Housewife’s scientific thinking
• She has only one observation
• Can’t draw valid conclusions from only one observation
• ex. I was born in Texas and now I am professor in Hong Kong
• Conclude people born in Texas move to Hong Kong
• She has confused “correlation” with “causation”
• Because vaccination occurred before the onset of autism symptoms, does not mean the
vaccine caused the autism

4. How does the scientific community address
these issues?
• Large sample sizes.
• A recent study examining the link between the MMR vaccine and
autism examined 95,000 children
• http://edition.cnn.com/2015/04/22/health/mmr-vaccine-autism-study/
• Compared the risk of developing autism between children who had
the vaccination and those who were not vaccinated.
• “found no evidence that receipt of either 1 or 2 doses of MMR vaccination
was associated with an increased risk of ASD.“ (ASD – Autism Spectrum
Disorders)

5. How does the scientific community address
these issues?
• Conduct a controlled experiment.

6. Example Experimental Study
• Always start with a question!!!
• Do plants grow better when you fertilize them?
• State your hypotheses
• Based on our understanding of how nutrients affect plant growth we expect
that fertilizing plants will make them grow better. (hypothesis 1)
• But we can think of other possible hypotheses
• Fertilizing plants has no effect on their growth (hypothesis 2)
• Fertilizing plants has a harmful effect on their growth (hypothesis 3)
• Can you think of more possible hypotheses?

7. Example Experimental Study
• Plan your experiment
• We will manipulate the amount of fertilizer that different plants receive
• We will divide the plants into two groups
• fertilize some plants, but not fertilize other plants

8. Example Experimental Study
• Make Predictions
• If hypothesis 1 is correct
• Plants that were fertilized should be taller than plants that were not fertilized
• If hypothesis 2 is correct
• Plants that were fertilized should be the same size as plants that were not fertilized
• If hypothesis 3 is correct
• Plants that were fertilized should be shorter than plants that were not fertilized

9. Example Experimental Study
• Conduct the experiment
• Measure plant growth by measuring the size of the plants (e.g., height or mass) after
some period of time.
• Measure the height of the plant

10. Example Experimental Study
• If the results of our experiment showed
• Mean height of fertilized plants = 45 cm
• Mean height of unfertilized plants = 30 cm
• Then what would you conclude and why?

11. Example Experimental Study
• Compare your results to the predictions of your different hypotheses.
• The observations to not meet the predictions of hypotheses 2 and 3
• We can reject these hypotheses and conclude that they are not true
• The observations match the predictions of hypothesis 1
• We can conclude that these results support hypothesis 1
• Thus, we conclude that hypothesis 1 is the best hypothesis
• Do we conclude that our results “prove” that hypothesis 1 is correct.
• NO!!!!!!
• Be careful about using the word “proof” in science

12. Experimental Design
• A well-designed experiment includes
• Replication
• You include many subjects in your study
• E.g., make sure that many plants individual plants are fertilized and many individual plants are
not fertilized.
• Randomization
• Randomly choose which individual subjects receive which treatment
• E.g., randomly choose which plants are fertilized and which plants are not fertilized
• Control
• The control group is not manipulated in any way
• E.g., some plants were not fertilized
• Need to compare the results of your experimental manipulation to the results of your control
group to draw any conclusions

13. Experimentally testing link between vaccines
and autism
• We could vaccinate some children and not vaccinate other children
and examine the results.
• Question- Does the MMR vaccine cause autism?
• Hypotheses
• Hypothesis 1- MMR vaccine can cause autism
• Hypothesis 2- MMT vaccine can not cause autism

14. Experimentally testing link between vaccines
and autism
• Plan our experiment
• Some children will receive vaccines and others will not. We will test the
children to see whether or not they develop autism or not.
• Predictions based on different hypotheses
• If vaccines can cause autism then predict
• More vaccinated than unvaccinated children will become autistic.
• If vaccines can not cause autism then predict
• There will be no difference in the prevalence of autism in vaccinated and unvaccinated
children

15. Think About How You Design and Conduct
this Experiment
• Discuss how you would design a study that contained all the elements
of good experimental design
• Discuss what you think about the ethics of such an experiment.

16. Scenario
• Global climate change is a theory that is supported by most climate
scientists in the world who have concluded that the Earth has, and
will continue to get warmer as the result of human activity.
• Last January, when Joe Texas woke up and looked out the window he
was 20 cm of snow and noticed that the thermometer in the back
yard read “-10oC”. “Dang”, said Joe, “this is the most snow and the
coldest temperature we have had in 10 years! See, I told you that
global warming idea was ridiculous!”

17. Problems with Mr. Texas’ Scientific Thinking
• As you discussed in class there are many problems with Mr. Texas’
scientific reasoning.
• He sampled only one day
• In fact, he noted the observations that day because they matched his preconceived ideas
about how the world worked
• He confused “climate” and “weather”

18. Problems with Mr. Texas’ Scientific Thinking
• How could he improve his scientific approach?
• Observe the weather for more days in more places over a longer period of
time
• Could we conduct a manipulate experiment to test the hypothesis that
human activity is causing the global temperature to increase?
• Think about developing a well-designed experiment test
• Note- do not be afraid to THINK BIG!!

19. The Single Earth Problem
• A well designed experiment to test the hypothesis that human
activity is causing global climate change would
• Involve a number of replicated Earths
• Half would be randomly chosen to have people, half (the control group)
would be randomly chose to have no people
• We would measure the change in temperature over time on Earths with and
without people.
• What is the problem with this experiment??

20. The Single Earth Problem
• Because we are not able to do a well-designed and “properly-
controlled experiment” we are forced to look at new approaches to
examining the effect of human activity on the global climate
• Logic, use mathematical models as tools

21. Climate Models

22. Intended Learning Outcomes
• By the end of this course a fully-engaged student should be able to
• Analyze scientific arguments, evaluate their validity, and explain their
conclusions to fellow citizens (e.g., your roommate in the Hostel or you
brother/sister)
• List the characteristics of a well-designed manipulative experiment
• Design an experiment to help answer a particular question
• Analyze experiments and evaluate the effectiveness of the experimental
design and appropriateness of conclusions the study has drawn.