ENVR 1401

ENVR 1401

ENVR 1401

Capture-recapture Simulation 


The objective of this experiment is to study the use of capture-recapture in estimating population size.  Two methods of estimation will be used and compared. 


Two hundred pennies

Paper or opaque plastic bag

Tape or mailing label

Scissors (optional)


Creating your Lincoln-head penny population

Obtain two hundred coins of any single denomination, e.g. 200 pennies etc.

Put 100 of the coins into a bag. 

Of the remaining coins put another handful or two in the bag – do not count these coins.

Capture, Mark, and Release

Draw 25 pennies out of the bag.

Mark the pennies with a piece of tape or mailing label.  Be sure to mark the same side of each penny or mark both sides so you do not miss a marked coin on your recapture.

Put the marked coins back into the bag

Recapture and count

Draw 30 coins from the bag without looking.

Count the number of coins recaptured and put your data into Table 1. (Note:  an example of how Table 1 is supposed to look like has been provided to you at the bottom of the document.  You are expected to recopy the Table I , delete out the prefilled numbers and enter your own numbers and calculations).

If you do not recapture any marked coins or you only recapture one marked coin then repeat the trial without recording the results

The process assumes it is equally likely to get 25 marked coins as it is to get zero marked coins but the sampling technique used here is biased toward recapturing zero or very few marked coins.

If you want to keep a trial where only one coin is recaptured then double the number of trials you make from 6 to 12.

Replace the coins back into the bag without marking any of them.

Repeat recapture and count until Table I is filled.

Count the number of coins in the bag and record the value as P in Table II. (Note:  an example of how Table II is supposed to look like has been provided to you at the bottom of the document.  You are expected to recopy the Table II , delete out the prefilled numbers and enter your own numbers and calculations).


Look online for a free calculator program for descriptive statistics.

Enter the data and calculate the average values of P (mean) and their standard deviations

Calculate the percent difference between the actual number of coins present in the bag and the estimated average values using the two methods.  See: Lab 1.

Fill in Table II, where P is the actual number of coins in the bag, P1, and P2 are estimates using the two equations provided. 

Literature Review

Use this link to go to the CTC online library databases.

Click on the appropriate link to enter the logon procedure.

Follow the instructions to gain access to the CTC online databases.

Scroll to the Science & Technology Collection link and open the link.

You should be taken to the EBSCO Host Research Databases

In the Find text box, enter capture recapture

Click Search (You may want to search full text as well)

Look over the search results and read some of the abstracts to gain a better understanding of how current research applies capture-recapture methods to current issues.


Write a lab report for this activity.  Submit the report to the Report link online at the end of the lab.

Your lab report must include the following sections. 

Introduction – in the introduction discuss the topic of capture-recapture. Include any interesting facts you learned in your library literature review.  Also include a description of the issue you are studying in this experiment, that is, what is the hypothesis of this experiment?

Methods – in the methods section briefly describe how you performed the experiment.  DO NOT simply copy the procedure portion of these instructions. Include any issues you encountered in performing the experiment.

Results – in this section include a discussion of the results you obtained including Table I and Table II.  If you wish you can also include any histograms or graphs you choose to create. 

Discussion – discuss your results by comparing the accuracy of each method.  Discuss ways to improve the accuracy of estimates.
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