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Understanding Our Planet Through Chemistry

IV. Can We Depend on Chemical Analyses?

IVa. Measuring quality

The importance of measurements

One of the tasks facing scientists is to measure and define unknown quantities. These measurements are important because they can warn us of potential hazards from volcanoes and environmental contamination or help us develop our mineral resources to stay competitive in the worldwide economy. In Earth sciences, the measurements of geological samples are used in making policy decisions. These decisions can affect all Americans in topics ranging from pollution prevention and control to evaluation of mineral resources and wilderness areas.

Decisions are made every day based upon measurements of various substances (or areas containing them). Without quality measurements, misleading or dangerous conclusions could be drawn.

The uncertainty of measurements

There are many difficulties associated with making measurements. Quality assurance involves minimizing mistakes and correcting problems before the information is used.

When an archer releases an arrow at a target, both the distance from which the archer shoots and the size of the target define what is considered acceptable accuracy and precision. Shots from 5 yards would be expected to hit closer to the bull's-eye than shots from 50 yards. If the arrows miss the target completely, the archer is considered inaccurate. The closer together repeat shots hit the target to each other, the more precise the archer. The strength and dexterity of the archer, the acuity of the archer s eye, the adjustment of bow sights, wind conditions, and the number of shots taken also contribute to the accuracy and precision of the archer. A laboratory procedure is similar in the need to understand the variables involved and the possibilities for error.

Searching for the best

A mistake in measurements can impact decisions made on endangered animal habitat, mineral exploration, or remediation of an environmental problem. When a quality assurance program claims 99.9 percent accuracy, consider what that could mean in terms of error: 1 hour of unsafe drinking water per month, 16,000 lost pieces of mail per hour, or 176,000 checks deducted from the wrong bank accounts every day. The quest is for 100 percent accuracy and precision, even if it is not attainable.

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