Prosecution hypothesis: Suspect (S)
Defence hypothesis: Unknown (U)
Two simple examples to calculate the LR:
a) When S=ab and C=a (an example of dropout)
b) When S=ab and C=ac (an example of simultaneous dropout and dropin)
This spreadsheet shows how the calculations are made and you can input your own allele frequencies
Download LRcalc Spreadsheet
This model illustrates the basic principles of drop-out and drop-in theory.
Instructions:
1) Simple example of one allele dropout
2) Input an allele frequency in cell E2 (for simplicity, we can only use one frequency which is applied to both alleles of the (ab) heterozygote)
3) Input an appropriate level of C in cell C2 (probability of drop-in). A level of 0.05 is typical.
4) Press the button below (it says 'press me') and the macro will plot the LR relative to the calculations in the blue shaded cells below. We cycle through all possibilities of PrD 0 - 1 and produce the plot on the right from this data.
5) If you want to, you can change probability of Dropout (D)in cell A2 to provide an exact LR in cell I2.
6) Note that Dbar and Cbar (probabilities of no-dropout or drop-in are automatically updated
7) The second example also uses your input data in cells A2:D2