Tuesday, December 6, 2011

Surrogate Measurement vs Real Measurement

Surrogate Measurement vs Real Measurement is an issue in many things beside soils. The medical industry uses surrogate measurement for a lot of things.

Surrogate measurement is the concept of measuring something that generally relates to a desired property, that is difficult to measure. The swelling potential of soil is time consuming test, but the moisture content, liquid and plastic limits can be determined in a day. There is a direct relationship between the liquidity index and the swelling potential, so we determine the liquidity index and imply a swelling potential.

As long as that relationship between the liquidity index and swelling potential holds, we are in good shape. But add any one of a long and growing list, and we are out to lunch by a long shot. Gasoline, any petroleum, soap, or even organic staining, and the correlation is out. Now we must do the full consolation with swelling, to find one point. We may need a number of points, depending on the situation. Each point is 12 days at least, if a (the) consolidation frame is available.
We would need to do the test to even find out that the relationship does not hold for this sample.

Those time do not include any sampling time involved, nor sample quality issues.

Now what about the medical field. wtf. They use more surrogates than we do in engineering. If you are producing enough iodine in you urine, you are not short. 20 years of misery, and Oh, you are not absorbing enough iodine. wtf.

Oh well shit happens. The medical industry knows what it knows, which is considerable less than they indicate that they know. If they do not deliver results, they do not have a solution. Trying something may be the only true test of whether it will work or not.

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