Transcript Notes 1.3 - Collins Hill High School

Surveys, Experiments, and Observational
studies
Warm Up
Identify the population and the sample.
1. Fifty teenagers are randomly selected and asked
whether they have siblings.
population: teenagers; sample: the 50 selected
teenagers
2. Fifteen passengers on a flight are asked about
the quality of the flight attendants’ service.
population: passengers on the flight; sample: the
15 people asked
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
3. To determine how many cats have blue eyes, the
eye colors of 10 cats at each of 10 animal shelters
in different states are recorded.
population: cats; sample: the 100 cats whose eye
colors are recorded
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Objectives
Focus on the commonalities and
differences between surveys,
experiments, and observational studies.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Vocabulary
experiment
observational study
controlled experiment
control group
treatment group
randomized comparative
experiment
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
You have already seen that a survey is one way to
collect data. Although surveys are useful, different
situations require different techniques for gathering
data.
Individuals are people, animals, or objects that are
described by data. If you collect data on the fuel
efficiency of cars and trucks, the individuals are
vehicles. Variables are used to describe individuals.
Fuel efficiency, measured in miles per gallon, is an
example of a variable.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
For data from an experiment to be useful, the
experiment must be carefully designed. In a
controlled experiment, two groups are studied
under conditions that are identical except for one
variable. The effects of the treatment are
determined by comparing the control group and the
treatment group.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Often, to demonstrate a cause and effect
hypothesis, an experiment must show two things.
First, that a phenomenon occurs with the
treatment; and second, that the phenomenon does
not occur in the absence of the treatment.
In a randomized comparative experiment, the
individuals are assigned to the control group or the
treatment group at random, in order to minimize
bias. An experiment that is not a randomized
comparative experiment may be subject to bias, and
any conclusions drawn from the experiment may not
be valid.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Example 1: Identifying Experiments and
Observational Studies
Explain whether each situation is an experiment
or an observational study.
A. A researcher wants to know if a soil additive makes
a fern grow more quickly. He grows one specimen in
treated soil and one in untreated soil.
The researcher applies a treatment, so the situation
is an experiment.
B. To find out whether car accidents are more likely
on rainy days, a researcher records the weather
conditions during 50 randomly selected accidents for
the past year.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Continued Example 1: Identifying Experiments and
Observational Studies
The researcher gathers data without controlling the
individuals or applying a treatment. The situation is
an example of an observational study.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Check It Out! Example 1
A scientist measures the height of 20 birds’
nests, and counts the number of eggs to see if
there is a relationship. Is this experiment or an
observational study? Explain.
It is an observational study because an observation
is being conducted without controlling the
environment in any way
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Example 2: Evaluating a Published Report
The study described in
the report is a
randomized
comparative
experiment. Describe
the treatment, the
treatment group, and
the control group.
The treatment is bathing in Epsom salt. The
treatment group consists of the fifty subjects who
bathe in the Epsom salt, and the control group
consists of the fifty subjects who did not.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Check It Out! Example 2
The study described in the
report is a randomized
comparative experiment.
Describe the treatment,
the treatment group, and
the control group.
The treatment is using the old and new websites to
make purchases. The treatment group consists of users
of the website using the new website to make
purchases. The control group consists of users of the
website using the old website to make purchases
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Example 3: Designing an Experiment or
Observational Study
Explain whether the research topic is best
addressed through an experiment or an
observational study. Then explain how you
would set up the experiment or the
observational study.
The treatment may affect health, so it is not ethical to
assign individuals to a treatment group. Perform an
observational study. Randomly choose one group of
people who already use tanning beds at least twice a
month and another group which does not. Monitor the
incidence of skin diseases in both groups.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Check It Out! Example 3
Explain whether the research topic is best
addressed through an experiment or an
observational study. Then explain how you
would set up the experiment or the
observational study.
1000 mg of vitamin is not known to have any
negative effects, so conduct an experiment.
Randomly choose one group of people to take the
supplements, randomly choose another group of
people to not take the supplements, and monitor the
cholesterol levels in both groups.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Example 4: Evaluating Data Collection Methods
Classify each method as a survey, an
experiment, or observational study, and explain
which would be most reliable.
Method A:
Choose 50 people
who have at least
one serving of soy
a day and 50 who
don’t, and check
their cholesterol
levels.
Holt McDougal Algebra 2
Method B:
Method C:
Randomly choose
100 people. Ask
how many servings
of soy they have a
week, and ask if
their cholesterol
levels are high.
Randomly choose
50 people to eat at
least one serving
of soy a day, and
50 people not to,
and monitor their
cholesterol levels.
Surveys, Experiments, and Observational
studies
Continued Example 4: Evaluating Data Collection
Methods
Method A: observational study
Method B: survey
Method C: experiment
In Method A, the members of the study are selfselected. They may have a healthy diet in general. In
Method B, the results are self-reported, so they may
not be accurate. Method C is most reliable.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Check It Out! Example 4
Classify each method as a survey, an
experiment, or an observational study, and
explain which would be most reliable.
Holt McDougal Algebra 2
Surveys, Experiments, and Observational
studies
Check It Out! Example 4
Method A: experiment
Method B: survey
Method C: observational study
Method B is least reliable, because there is no basis
for comparison. Method C has a comparison group,
but the members are self-selected, which could lead
to bias. In method A, the members of each group
are randomly selected, so method A is the most
reliable.
Holt McDougal Algebra 2