Capture-Recapture

Actually my colleague Michael's lesson, but he generously allowed me to blog about it, because I thought it was a great and cute idea. I'm retelling it as closely as I can to the way he told it.

"There's plenty of fish in the ocean. But how many?"

"Here's the ocean. You can tell because it has fish in it. And a sea monster. Who is willing to brave the sea monster and go fishing?"

"You got a fish!" A yellow counter is removed. "What kind of fish is it? It must be a goldfish!" More yellow counters are removed. "They're all goldfish!".

"We've removed 20 fish. Now we are going to tag them." Twenty removed yellow counters are replaced with red counters. And returned to the ocean.

The ocean is shaken around for a bit.

Now the fish are recaptured in different sized samples and the results of tagged-untagged recorded. These are used to estimate the number of fish in the total population (a number unknown even to the teacher).

Then, since our ocean is only a small ocean, the real number can be found and compared to these values, and we can start asking the interesting questions. Which was the closest estimate? How did sample size in the recapture change the estimates? How accurate is capture-recapture?

I'm pretty sure now that all spare cardboard boxes should become monsters of some kind.