Scientific analysis can only be useful if the data a scientist gathers is accurate.  However, there are many ways in which errors can occur in environmental measurements.

One major problem is that a scientist's instruments may not be good enough for their work.  To ensure accuracy, instruments must be calibrated to a standard reference frequently.  The National Institute of Standards and Technology is the basis for most internationally used measurement standards.

Every time we take a measurement, we must take potential error into account.  Specifically, a scientist has to look at potential problems arising from the degree of inaccuracy of the equipment being used.

Accuracy refers to the amount of similarity to the real or reference level or a measurement.  After a measurement is made, it can be compared against a standard.  This can generate a level of accuracy for the scientist.

Precision means the amount of reproducibility of an experiment.  If a scientist repeatedly conducts identical experiments, she can compare the level of similarity in her results to determine the level of precision. 

As a result, it is possible, though unlikely, that a highly precise result could also be highly inaccurate.  A scientist that conducted multiple studies showing very high air pollution rates would not be able to claim correctness solely by virtue of great precision.

Usually, scientists report their level of precision using the coefficient of variation.  As with standard measures, a standard error-reporting system helps to simplify statistical analysis.