New to MARK, question about interpreting results

[bshepard]

Hello all,

I am new to using this program, as well as new to this type of analysis, and I have a couple questions about interpreting some results.

I used POPAN to analyze my mark recapture data from a study on lizards. For the data set I am looking at we had continuous marking, and 6 recapture occasions, for a total of 7 sampling occasions. We had marked a total of 75 lizards for this plot by the last day, and we had figured on there being not too many more based on some previous work. However, the N estimate that I am getting now is orders of magnitude larger than what we had expected (N= 3990.1855). I am not sure if I did something very wrong with how I built my data matrix, or if I just misread in the "gentle introduction" how to interpret these results.

This is how the data is arranged.

1001110 1;
1000000 2;
1000000 3;
1000000 4;
1001100 5;
1000010 6;
1011100 7;
1101011 8;
1000000 9;
...

Can anyone give me a hint as to what I need to know or do? I can supply more information as requested.

thanks.

[bacollier]

bshepard,
I think your problem may be with your input file if it is exactly as shown. Based on the data, your first encounter history you are saying you have 1 individual with that history, for your second row of data, you are saying there are 2, for the 3rd three, so on up to 75. So, you are telling MARK you have 1+2+3+4...+74+75=around 2850 individuals. I bet if you change all those to 1 (assuming each row represents a unique record), then you will probably get answers more in line with what you were expecting.

Make this:

1001110 1;
1000000 2;
1000000 3;

into this:

1001110 1;
1000000 1;
1000000 1;


Bret

[claudiapenaloza]

In your encounter histories, the last number before the semicolon (i.e., the count)... Why are those in ascending order?
Did you have one individual with the encounter history in the first row, two with the encounter history in the second row, three with the encounter history in the third row, and so on?
That is what this number means, it tells MARK how many individuals had the preceding encounter history... I assume this is not what you meant when you built the encounter histories because your second, third and fourth row of encounter histories are identical, which sort of defeats the point of summarized encounter histories (i.e., encounter history files where the "count" is different than one and indicates how many individuals had a given history).

I think if you fix this and put a "1" in the count (for non-sumarized encounter histories) your estimates should "fix themselves"... they way they are now, you are basically telling MARK you've marked and recaptured many more animals than you really did.

Good luck,
cp

[bshepard]

Thank you very much.