Applying Scientific Thinking:Suzy Housewife and Joe Texas

Dr. Mark A. McGinleyProfessor, Head of Science Unit

Core Curriculum and General Education OfficeLingnan University

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.

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

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)

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

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?

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

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

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

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?

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

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

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

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

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.

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!”

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”

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!!

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??

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

Climate Models

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.