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Jun 23, 2011

cross over point of two populations

Hi fellow JMPers,

I need to calculate the cross-over point of two populations.  Example

measurement group

1    A

2    A

3    A

4    A

5    A

5.5    A

6    A

5.4    B

5.8    B

6.2    B

7    B

8    B

9    B

10    B

The One-way plot looks like this.


As you can see, the maximum of "A" group is larger than the minimal of the "B" group.  So there is a cross-over point of measurement value where we have equal percentage of "A" and "B".  It is easier to visualize if one group is "flipped" by invert its normal quantile.   In the example, it is about 5.68 & -0.833.


The question is, how to calculate this point (value & probability) programmatically?  I am having trouble to ID the four points around the crossover reliably.