Population
Sampling Homework
Assume you capture and weigh a sample of Gila aardvarks in the
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1. Calculate the mean weight of the sample of aardvarks.
2. What is the range?
3. Calculate the variance (s2) of the sample. The variance is the sum of all
individual deviations squared, divided by (n-1). In other words do the
following:
a.
Determine the deviation of each data point (subtract the sample mean from each data point). Some of your values will
be negative numbers, but that's OK.
b.
Square each individual deviation.
c.
Add all of the squared deviations together.
d.
Divide this sum of deviations squared by the sample size minus one (n-1). The product of this division is the sample
variance.
4. Calculate the sample standard deviation (s) simply by taking the square root
of the sample variance.
5. The standard error of the mean (SEM) can be calculated by dividing the
standard deviation by the square root of the sample size. Calculate the SEM.
6. The reporting of descriptive varies among scientific disciplines, but a
common way of reporting them (and the way we will report them in this class) is
as follows:
Mean ± SEM, n = ?
Write your answer in the above format:_________________________________
7. What is the basic problem associated with a large sample size?
8. What is the basic problem associated with a small sample size?
9. How do you know if your sample size is large enough? Again, opinions vary among scientists. Many biologists use this rule-of-thumb: the sample is large enough if the SEM is less than 10% of the sample mean. Recall that sample size is in the denominator of the SEM, so the larger "n" is, the smaller SEM is. Based on this guideline, would you conclude that your sample of Gila aardvarks is large enough to provide you with a reasonable description of the entire population?