Create a classification matrix

- [Instructor] In the previous movie,…I showed you a way to draw a graph…that visualizes the way probability is combined…to perform Bayesian analysis.…In this movie, I will show you…how to create a calculation matrix…which will take us one step closer…to implementing the analysis in Excel.…So let's review what we know…about our base rates and accuracy.…Based on what we stated before,…85% of cabs are green, and 15% are blue.…The accuracy of witness testimony is 80%,…so 80% of the time, they'll be right, 20% wrong.…

The cab can be either green or blue.…Those are the only options.…And the witness can be accurate or not.…And using those facts,…we can create a table by evaluating…the probability of each case.…So how do we create a classification matrix?…Well, again, we have green cabs 85% of the time,…blue cabs 15,…witness is correct 80% of the time,…and incorrect 20%.…Here is what the matrix looks like.…We have our four cases…where the cab was reported as green…and was actually green,…and that will occur 68% of the time, .85 times .8.…