Why is Chapman highlighted?

It behaves better for smaller samples and low recapture counts.

What if R is very small?

The estimate becomes unstable. Try increasing the second capture effort if possible.

Enter first capture marked, second capture total, and marked recaptured to estimate population size.

Answer

238

Chapman estimate

Lincoln-Petersen estimate: 250

Approx. 95% interval: 142 - 334

Standard error: 49

Recapture rate: 20%

Marked in first sample (M)Captured in second sample (C)Marked recaptured (R)

Examples

Sampling checks

Marked share of first sample	Unmarked in second sample	Standard error	Approx. 95% interval
24%	48	49	142 - 334

Chapman = ((M+1)(C+1)/(R+1)) - 1; Lincoln-Petersen = MC/R

The Chapman estimate is shown first because it reduces small-sample bias compared with the simple Lincoln-Petersen ratio.

Symbol	Variable	Description
M	Marked first sample	Individuals marked and released in the first capture.
C	Second capture	Total individuals captured in the second sample.
R	Recaptured marked	Marked individuals found again in the second capture.

1
Enter capture counts
Use M for marked first sample, C for second capture total, and R for marked recaptured.
2
Read Chapman estimate
Use the highlighted Chapman value for most small field samples.
3
Check uncertainty
Low recapture counts usually create a wide interval.

Use the estimates and interval together when reporting mark-recapture results.

Result	Meaning
Chapman estimate	Bias-corrected population estimate
Lincoln-Petersen	Simple ratio estimate
Recapture rate	R divided by C

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