calculate area under a two way graph

[Sunil Sampath]

I need to measure the area under a curve in a simple two-way graph (please see attached image) Graph.tif
The graph was not obtained by fitting a logistic model, hence cant use the stata's lroc command.
Any help greatly appreciated.
Many thanks

[Roman Mostazir]

We can't see what you have attached (at least I can't). Please read the FAQ section on how to make meaningful post. If you are looking for area under curve (AUC) estimated by integral function, this thread may help.

[Nick Cox]

You should be able to calculate the area as the sum of areas of trapezia, With two adjacent y and x values, the area of each trapezium is just

(first y + second y)(larger x - smaller x)/2

but also

help integ

[Sunil Sampath]

Hi Roman - sorry the image didnt show (I had upladed a .tiff file)
Nick- many thanks again for your very helpful response.
kind regards
Sunil