A sample is that portion of the population which is actually measured. Sampling is a more practical way to obtain inventory or monitoring information because not all members of the population need to be measured. It permits data to be obtained at less effort and expense, and may enhance its integrity by reducing mistakes associated with the tedium of prolonged repetitive measurements.
Frequency data may be analyzed by several different techniques, depending upon how the sample units were located and how the data was collected.
The appropriate statistical model for analyses to identify differences in cover between years or among sites depends on the method to determine cover that was followed, and decisions defining sample units made during preliminary planning.
Ground rules are guidelines developed to minimize the subjectivity of sampling. Ground rules should be developed before field work commences, and should be clearly included in the sampling protocol. Ground rules are especially important to maintain sampling accuracy and precision when a number of different people are involved in data collection, or when data is collected over a number of years.
Resource value ratings have been proposed as an approach to meet the demands of multiple use principles, by evaluating the suitability of the current vegetation for a specific use, such as livestock grazing, desert tortoise habitat, and recreation. Therefore, it is appropriate to assign several resource value ratings to each range site.