I.) Defining the Sampling Universe and Unit+Variables Flashcards
Sampling Universe (Block)
The area that is covered in a single sampling program.
Includes determining the boundaries for which a specific pest management decision is made.
Such as a whole field of corn or several smaller areas of a field (though if blocks have different varieties, planting times, or envm. conditions, then it is best to sample them independently from one another).
Sampling Unit
The measuring unit of a sample size. May consist of a leaf, a square foot of soil (Daubenmire square), a net sweep sample, or a soil auger core.
Should adequately asses the target pests population (size, abundance, distribution pattern, mobility, etc.), though at the same time economically feasible.
The smaller the sample unit size and more samples collected,
generally, the better the information about the population.
Sample Accuracy
How near the sample average is to reality. (e.g. how close the shots are to a bullseye)
When precision is poor, accuracy can be improved by increasing the number of samples.
As the pest population approaches the action threshold, more samples should be taken to improve accuracy. Otherwise, treatments may or may not take place when actually needed.
Factors affecting Accuracy
Affected by the efficacy of finding the pest, how fast it proliferates, and distribution behavior.
On the PCA’s side this includes choice of the sampling device, methods, and how carefully the samples are taken.
Consciously sampling hot spots (bullseye-where the pest hangs out) is a good strategy to detect early infestation and more easily find beneficial insects; though should not be used to make treatment decisions for an entire field.(Rather serve as an early warning system).
When using scouts; clearly define the sampling unit and methods for selecting samples in order to minimize error in technique.
Sample Precision
Refers to the variability among samples. (e.g. how centered is each bullseye-shot or not)
When precision is low, standard deviation is high.
Factors affecting Precision
Affected by the biology of the pest (distribution patterns) and characteristics of the sample universe (field size or shape).
Small and irregularly shaped fields require more samples per unit area to provide precise results than do larger more uniform fields.
The less that is known about the pest, the more samples that should be taken in order to establish the optimal sample size.
When lacking research based recommendations on the number of samples needed to provide precise results, the following can be estimated by calculating the mean and variance of preliminary samples as described in the “General Formula to Determine Fixed Sample Size.”
