Slide 10 of 17

These examples illustrate error variance. Any sampling procedure produces error.

1-Channel sampling of gravel is shown on the left. Repeated sampling of the same channel cut in gravel will yield samples having slightly different values for a characteristic, such as average particle size.

2-Repeated measurement of a characteristic, such as would be obtained by re-sieving a sample to determine average particle size, will yield different results, also. The differences measure the error of the sieve method.

3-Error variance is the sum of sampling and measurement.

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