Determine Population Size
Message posted by Ed Clark on March 24, 2000 at 12:00 AM (ET)

How can the size of a population be determined by sampling? Poisson distribution?

READERS RESPOND:
(In chronological order. Most recent at the bottom.)

Re: Determine Population Size
Message posted by Phil Rosenkrantz on March 25, 2000 at 12:00 AM (ET)

To calculate hypergeometric probabilities you need:

N = Population size
n= Sample size
d= number of successes in the population
x= number of success in the sample

We normally solve for x, but you want N.

So, what you do is create a population of successes of size d and mix it into the population (e.g. mark some fish an dump them in the lake). Let the population mix so it becomes randomized.

Now, after the population has randomized, take a sample of size n from the population and see how many of the population are "successes". This number equals x (e.g. marked fish).

Using the ratio of x/n as an estimator of the hypergeometric probability of success, work backwards and determine what the "most likely" value of N would be to give you the resulting probability.

Hope that makes some sense. Obviously you have to be able to "salt" the population with successes to make this method work. This method hinges on knowing what "d" is.