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This activity page will offer:
- Introduction
to population sampling
- Application
of sampling technique
- Opportunity
to relate sample size to estimate accuracy
Population
Sampling
In this activity, you'll infer numbers of a virtual population illustrated
within a rectangular sampling grid. You'll observe the accuracy
of the technique in relation to the sample size upon which the estimates
is based.
Materials
Click here for a larger version of
this grid
Steps
- Examine the counting grid above. It represents an area that
measures four meters by six meters. What is the total area of
this full-size grid?
- Make a guess before you do any counting. Estimate the number
of fish found within these 24 square meters?
- Use a pencil and number the squares one through 24.
- Devise a method for picking six random numbers from that same
range of twenty-four numbers .
- Examine the six squares identified by the selection of your
six random numbers.
- Tally the total number of fish found in these six squares. Remember,
you'll need to devise a plan to deal with fish that lie on a dividing
line.
- Once you've tallied the number of your fish in your sample,
multiply this number by four. The number you arrive at is the
estimate for the number of fish in the24 square meter grid. Record
this as your first estimate.
- Pick three random squares. Tally the total number of fish in
these squares. Multiply your count by eight. Record this value
as your second estimate.
- Randomly select one number. Count the number of fish in that
square. Multiple this number by 24 to arrive at an estimate of
the number of fish in the entire area.
- Repeat step 9 two more times.
- Count
the actual fish that are in the entire grid. Compare and contrast
this number to the estimates made based upon 6 samples, 3 samples,
and the 1 sample calculations.
Questions
- Why was it important to devise a way of picking random numbers.
- Why did you need to develop a method for counting fish that
were positioned on a grid line?
- In step 7, why was the number of counted fish multiplied by
four?
- How did the number of samples on which the estimate was based
affect the accuracy of the estimate?
More
Math
Based upon your count and observed concentration, how many fish
can be found in a square kilometer with the same population density?
Creative
Journal
Based upon the natural history of the salmon, create a fictional
journal that describes life as a salmon. Begin the story with the
salmon's hatching within in a remote lake in Washington. Be sure
to include entries that describe the hazardous journey both down
and up river.
Build
A Model
Research the structure of turbines and generators that are used
in hydroelectric plants. Then, use classroom materials to construct
a simple model of these devices. Include a model turbine with blades
that rotate in response to the flow of water. If applicable, attach
a small magnet to the turbine shaft. Place a coil of wire around
the magnet and monitor the inducted current using a digital multimeter.
Web
Connection
The
Life History of the Pacific Salmon
http://biology.usgs.gov/wfrc/cook.web/start.htm
Hyperlinked photographs explore the life cycles of different types
of Pacific Salmon
Sampling
in Research
http://trochim.human.cornell.edu/tutorial/mugo/tutorial.htm
An introduction to sampling and sampling errors.
Identifiying
Populations
http://www.nwfsc.noaa.gov/cri/pdf_files/UpperCol.PDF
A paper written by scientists on the subject of salmon population
structure.
Academic
Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools, Wayland,
MA
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools,
Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland,
MA
Gary Pinkall, Middle School Science Teacher, Great Bend Public Schools,
Great Bend, KS
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