Population Sample Survey
Name: ______________________
Problem: How do scientists determine population size in a large area such as a state
park?
Background:
A very important part of environmental and ecological studies is
understanding how to determine a valid population estimate or index when it is
impractical or virtually impossible to count all organisms in a population for a specific
area.
For example, let’s say that scientists are trying to determine the deer population in
a specific 1,000 acre area.
Physically counting all of the deer in this area would be time
consuming and impractical; however, by randomly choosing several smaller areas - 10
area plots, for instance – and extrapolating or applying that information, the scientists
could obtain a fairly accurate estimate of the number of deer per 1,000 areas.
Let’s say that based on random sampling, the scientists estimate that there are 40
deer per 1,000 acres.
This number is known as a population index.
This population
index can then be compared to previous and/or future indices, to determine fluctuations
in population numbers over time.
In the previous example, the word “random” occurs several times.
In order to be
scientifically correct and used as a basis for making scientific conclusions, a population
estimate or index must be representative, or random.
be totally random and free of biases.
This means that the sampling must
For instance, let’s say the scientists know that a
herd of deer is located in a particular area.
If they always choose this area to do their
sampling, their results will be biased or skewed.
However, if they randomly choose
several different areas in the 1,000 acre tract to sample, and then average their results,
the population estimate will be more representative of the entire tract.
Representative (random) sampling could involve several thousand acres or be
confined to a slide under a microscope or an aerial photograph.
Many factors must be
considered in selecting the appropriate, “statistically correct” sampling technique for the
population being surveyed.
This model represents a very basic sampling.
Indeed, the
primary objective of this model is to stimulate thought while introducing students to the
concepts of random, representative, and statistically correct sampling.
Hypothesis: If the ___________________ study technique is used, then it will show that
there are _______ wild “pinto beans” because __________________________________________
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(explain why this sampling method is best)
Materials:
Wild Beans container
Sample field
Cardboard fence
Numbers
Procedure:
1. Complete the hypothesis, predicting how many beans live in the “park” area.
2. Clear a space in the middle of tables or on the floor.
Lay out the Sample field
and place the cardboard fence around the perimeter.
3. Carefully hold the container of beans about 3-4 inches above the sample field.
Distribute the beans by pouring them randomly over the surface.
to bounce freely.
Allow the beans
Once this is completed, be careful NOT to bump or move any
beans.
4. Shake the container of numbered squares and then draw one out. Locate this
square in your field.
Count the number of beans in this square, remember not to
touch or move the beans. Record the amount in the data table.
5. Return the numbered square to the container.
Select another number, count the
beans and record the amount in the data table.
6. Repeat this procedure for a total of 10 trials. Remember to put selected numbers
back into container before drawing another number out.
It is okay if you select
the same number… that’s what makes this method random.
Data Table:
Trial
1
2
3
4
5
6
7
8
9
10
Total
Average
Total ÷ 10
Estimate
Multiply by 100
Location
Bean Count
Population Sample Survey
Name: ______________________
Analysis:
1. Calculate the Total, Average and Estimate for the bean population.
2. Write your estimate in the table on the board.
This will be used to calculate a
class average.
3. Compare your group’s estimate to the other groups’ estimates.
How similar are
these numbers?
4. Based on actual data, how accurate is the sampling method of counting?
5. Was your calculated estimate within 10% of the actual number? Explain.
6. How could you use this method to count the number of fish, insects or people in
a certain area?
Conclusion - Learning Log: On space provided (or typed), write at least a paragraph
conclusion (at least 5-7 complete sentences per paragraph):
 Passive voice; no pronouns (NO – I, you, we, they, our, us, etc) [2pts]
 Restate the problem/hypothesis (in your own words), [2pts]
 Summarize the experiment- explain what was being tested for and how
(not a step by step explanation). [2pts]
 Provide evidence/data that will be used to support conclusion (data
from table). [2pts]
 Answer the problem using the hypothesis and data as part of the
explanation (conclusion). [2pts]
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