Exam (elaborations)
BIO 130M Introduction to Environmental Science Understanding_Experimental_Design_lab_Worksheet
- Institution
- Arizona State University
BIO 130M Introduction to Environmental Science
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Section 1: What makes a good experiment?Introduction to the Plight of the Simploids
Many are shriveling up and even dying. The population of Idyllic is very sad to lose their
Simploids.
They have proposed 3 hypotheses about what is happening to the Simploids. Record them
here for future reference. Hint: you have to watch the video.
1. Some of the simploids appear to be infected with a parasite, commonly called
shamworms.
2. Some citizens of Idyllic are using a new herbicide on their lawns, called ZapWeedz, in
order to control invasive weeds.
3. Some residents. Speculate that recent weather has been hotter and drier than usual,
which is affecting the Simploid’s health.
How Science Really Works diagram
Testing ideas can lead to (and these lead back to testing ideas)?
1. Benefits & Outcomes
2. Exploration
3. Community Analysis & Feedback
Under which heading/box is “gathering & interpreting data”? Testing Ideas
Well-Designed Experiments
What is difference between observational studies (such as the example given that people who
eat Mediterranean diets live longer) and well-designed experimental studies? Can
observational studies demonstrate cause and effect?
Observational studies can suggest associations between two variables, but they cannot establish
change in the other-the association may exist because both variables are affected by a third factor
that was not observed. Well-designed experiments, which systematically vary the hypothesized
causal variable (diet) and measure the response of interest (longevity), can researchers infer
causality.
Components of well-designed experiments:
1. Independent or treatment variable that you manipulate. The two categories of
treatment include;
1. experimental group that experiences the proposed treatment, and
2. control group that does not experience the effect of the treatment so that you
can compare the experimental group to the control group to determine effect of
the treatment.
b. Potentially confounding variables must be kept constant between groups
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, 1. For example, if you were testing the effect of the Mediterranean diet, you would
need to make sure both groups received the same amount of exercise, sunlight,
work conditions, etc., as these could be confounding variables.
b. Dependent (or outcome) variable that changes as a result of treatment
1. If you were going to perform a well-designed experiment about the effect of diet
on health and longevity, the dependent variable is health and longevity. You can
measure this in a number of different ways, but the most obvious is lifespan.
Make sure you understand the difference between these variables above, and how
they are related in the context of a hypothesis. You will be asked to identify them on the
lab quiz in Blackboard in the context of different examples.
Q1.2 Suppose you decide to design an experiment to test your friend’s hypothesis about
classical music and studying. How will you define your variables? Record your answer here.
a. Both study music and test performance are potentially confounding variables.
b. Independent variable: study music. Confounding variable: test performance
c. Independent variable: study music. Dependent variable: test performance
d. Independent variable: test performance. Dependent variable: study music
Q 1.3 In the experiment about music and studying, what would you call the group of people that
listen to classical music while studying? Record your answer here.
a. Control group
b. Experimental group
Scope of Inference
In order to be confident in the relationship that you observe between the independent and
dependent variable, you need plenty of data points. Replicates are multiple iterations of the
same experiment to insure that the relationship between variables holds under multiple
conditions and repetitions of the experiment. Also, it’s important to assign experimental units to
groups randomly to avoid relationships that are not truly there.
Q1.4 In the “puppy therapy” experiment discussed in SimBio, what was the experimental unit?
a. a single student
b. a section in the course
c. the entire course
Q1.5 In the “puppy therapy” experiment, how many replicates were there and how many people
does this include in total?
3
Q1.6 What could help improve the scope of inference for this experiment?
Conducting the experiment multiple times during the semester, and not just a singles week.
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