RMS

I wonder if there is anyone around who remembers RMS -- or more importantly: how it's used in PM? If this sounds a bit technical, but don't bail yet. It's a lot simpler and more actionable than the much more complex Six Sigma idea. In the Sixer world,

*defined process control*was the major outcome, and we were told that it was practical to obtain the data to drive the statistics.

__Nonsense__, for the most part, in PM. Projects don't usually have the historical data in reliable form to drive process control limits to anywhere like six sigma; most projects live in the "one sigma" world.

And that reality, one sigma, brings us to RMS! "Root of the Mean of the Squared-error"

**Application**

It's really not that bad, and: It's actionable by PMs! Here's a question you could answer with RMS analysis:

If it costs the project $100 to discover/fix a page error in a deliverable document,what's your risk exposureif you plan your project anticipating finding 1000 errors at an average discovery/fix of 3 per page? Your budget is: $100 * 1000 errors = $100K; or 333 pages * $300/page = $100K

**Example**

To answer that question, here's an example of how RMS analysis works:

Let's say you have a team working on documents, and you've based the budget on a reasonable number of errors/fixes in the documents: say3 errors per page. In effect, 3 errors/page is the mean error rate that drives your project estimates for time and labor to discover and fix the errors.

Now, suppose you get a monthly report from your work package manager that gives the following four observed errors per page in various documents in process: 1,2,5,4

The errors, relative toplanning mean,are the difference between the actual observed error and the planning mean. For the first one we compute (1-3) = -2; for the others, applying the same protocol: -1,2,1. (It actually doesn't matter if you adopt the opposite protocol: 3-1 = 2, if you are consistent)

Thesquared errorsare: -2 * -2 = 4; and 1,4,1. Themean-squared erroris average of the squared-errors, computed as: (1/4)(4+1+4+1) = 2.5 errors-squared.

Now, as a practical matter we can't work with something dimensioned as errors-squared, so we just take the square root to get the dimension back where we can use it.

And (drum roll goes here), the RMS is the sqrt (2.5) = 1.59 error/page (Call it 1.6 or even 1.5, since we're only talking planning stuff here, not trying to navigate to the moon)So can we answer the question about risk exposure?

Yes: By virtue of a couple of statistical theories, we can say:

Expect any similar document page errors to be more likely within +/-1.6 error/page of the planning mean than elsewhere.

Thus, anywhere fromIn short-hand, our expectation is:about (3 - 1.6) =to about1.4(3 + 1.6) =is where4.6most of the results are expected to be.

*Planning mean +/- RMS.*

**Exposure:**

Now, calculate the exposure: The best approach is to use the figure of 333 pages. Most of the cost (not budget) to discover/fix errors will likely be between:

- 333 * 1.4 * $100 = $47K, and
- 333 * 4.6 * $100 = $153K

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