This is part Twelve of the continuing series on two-filter document culling. (Yes, we are going for a world record on longest law blog series.:) Document culling is very important to successful, economical document review. Please read parts onetwothreefourfivesixseveneightnineten and eleven before this one.

Review of Basic Idea of Two Filter Search and Review

Whether you use predictive ranking or not, the basic idea behind the two filter method is to start with a very large pool of documents, reduce the size by a coarse First Filter, then reduce it again by a much finer Second Filter. The result should be a much, much small pool that is human reviewed, and an even smaller pool that is actually produced or logged. Of course, some of the documents subject to the final human review may be overturned, that is, found to be irrelevant, False Positives. That means they will not make it to the very bottom production pool after manual review in the diagram right.

In multimodal projects where predictive coding is used the precision rates can often be very high. Lately I have been seeing that the second pool of documents, subject to the manual review has precision rates of at least 80%, sometimes even as high as 95% near the end of a CAL project. That means the final pool of documents produced is almost as large as the pool after the Second Filter.

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Please remember that almost every document that is manually reviewed and coded after the Second Filter gets recycled back into the machine training process. This is known as Continuous Active Learning or CAL, and in my version of it at least, is multimodal and not limited to only high probability ranking searches. See: Latest Grossman and Cormack Study Proves Folly of Using Random Search For Machine Training– Part Two. In some projects you may just train for multiple iterations and then stop training and transition to pure manual review, but in most you will want to continue training as you do manual review. Thus you set up a CAL constant feedback loop until you are done, or nearly done, with manual review.

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As mentioned, active machine learning trains on both relevance and irrelevance. Although, in my opinion, the documents found that are Highly Relevant, the hot documents, are the most important of all for training purposes. The idea is to use predictive coding to segregate your data into two separate camps, relevant and irrelevant. You not only separate them, but you also rank them according to probable relevance. The software I normally use, Kroll Ontrack’s EDR, has a percentage system from .01% to 99.9% probable relevant and visa versa. A very good segregation-ranking project should end up looking like an upside down champagne glass.

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A near perfect segregation-ranking project will end up looking like an upside down T with even fewer documents in the unsure middle section. If you turn the graphic so that the lowest probability relevant ranked documents are on the left, and the highest probable relevant on the right, a near perfect project ranking looks like this standard bar graph:

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The above is a screen shot from a recent project I did after training was complete. This project had about a 4% prevalence of relevant documents, so it made sense for the relevant half to be far smaller. But what is striking about the data stratification is how polarized the groupings are. This means the ranking distribution separation, relevant and irrelevant, is very well formed. There are an extremely small number of documents where the AI is unsure of classification. The slow curving shape of irrelevant probability on the left (or the bottom of my upside down champagne glass) is gone.

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The visualization shows a much clearer and complete ranking at work. The AI is much more certain about what documents are irrelevant. To the right is a screenshot of the table form display of this same project in 5% increments. It shows the exact numerics of the probability distribution in place when the machine training was completed. This is the most pronounced polar separation I have ever seen, which shows that my training on relevancy has been well understood by the machine.

After you have segregated the document collection into two groups, and gone as far as you can, or as far as your budget allows, then you cull out the probable irrelevant. The most logical place for the Second Filter cut-off point in most projects in the 49.9% and less probable relevant. They are the documents that are more likely than not to be irrelevant. But do not take the 50% plus dividing line as an absolute rule in every case. There are no hard and fast rules to predictive culling. In some cases you may have to cut off at 90% probable relevant. Much depends on the overall distribution of the rankings and the proportionality constraints of the case. Like I said before, if you are looking for Gilbert’s black-letter law solutions to legal search, you are in the wrong type of law.

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Almost all of the documents in the production set (the red top half of the diagram) will be reviewed by a lawyer or paralegal. Of course, there are shortcuts to that too, like duplicate and near-duplicate syncing. Some of the documents in the irrelevant low ranked documents will have been reviewed too. That is all part of the CAL process where both relevant and irrelevant documents are used in training. If all goes well, however, only a few of the very low percentage probable relevant documents will be reviewed.