then she might conclude that 10% of the fish are trout. Obviously, the larger the unbiased random
sample of all the fish, the better will be the estimate of the fraction that is trout. Our ecologist captured
the fish with a net that has openings 2 inches wide. The smallest fish of the 300 she caught was 3 inches
long and 0.75 inches wide, and the largest was 18 inches
long and 7 inches wide. The “mean” (an
estimator of the average) length was 6.3 inches (add the length of all the fish in the sample and divide
by 300 = mean length). Two fish were 5.9 inches long and there were 149 fish longer than 5.9 inches
and 149 shorter than 5.9 inches. Thus the
“median”
(a different estimator of the average) length was 5.9
inches. Note that the median and the average are not the same. If she caught only 100 fish
all but 3
were shorter than 4 inches but 3 were huge sturgeons, all 100 inches long, then it is easy to see that
the median value, which was 3.4, would be a better estimate of the average, than the median value,
which was 6.4 inches, including the huge sturgeon. That is, the median better represented the
condition of fish in the lake than did the mean.
1.5.
Experimental Section: What Makes a Cricket Chirp?
Some say that if you listen to the sound of a cricket chirping, you can determine the temperature. Is this
true or is it just an urban legend? Do any other factors affect how fast a cricket will chirp, such as
humidity, wind, atmospheric pressure, or nearby crickets?
For this lab exercise, students will form into several groups and use a virtual lab to analyze a cricket
subject to collect data they will then share with one another.
1.6.
Materials:
1.
Access to Blackboard
2.
Computer with Internet Access

12
ENSCI099
–
A Practical Guide to Environmental Choices
1.7.
Procedure:
1.
Ensure that you carefully read the background material including all of the lab lesson before
coming to the lab and participate in the laboratory discussion.
2.
Go to:
and begin the Cricket
Experiment. Read through the introduction, define the problem, collect information, and then with
your group members, formulate a hypothesis.
3.
To perform the experiment, your group needs to collect data on each of the parameters (air
temperature, atmospheric pressure, humidity, number of crickets nearby and wind speed). Regardless
of the hypothesis your group comes up with, you must select a different factor during the
“Formulate
a
Hypothesis” step of the cricket experiment in order to test that specific
factor.
4.
Each lab group will collect information for each of the variables:
•
Air Temperature (5C
–
45C)
•
Atmospheric Pressure (680mm
–
790mm)
•
Humidity (10% - 80%)
•
Number of Crickets Nearby (0
–
20)
•
Wind Speed (0
–
7m/s)
5.
Your lab group must run the experiment several times for each of the variables, using the values
provided in the excel sheets. This will allow you to test the full range of each parameter.