In mathematics, a function
on the real numbers is called a step function (or staircase function)
if it can be written as a finite linear combination of indicator
functions of intervals. Informally speaking, a step function is a
piecewise constant function having only finitely many pieces. The
graph of a step function looks like a series of small steps.
(q) More than
type ogive
(r)
Subjectivist's criterion in decision making
(s) Double
sampling
Double sampling is a sampling method which makes use
of auxiliary data where the auxiliary information is obtained through
sampling. More precisely, we first take a sample of units strictly to
obtain auxiliary information, and then take a second sample where the
variable(s) of interest are observed. It will often be the case that
this second sample is a subsample of the preliminary sample used to
acquire auxiliary information.
The double sampling method was developed as a modification of the weight-estimate method, to attempt to overcome the lack of precision among observers and the possibility of unchecked drift in an individual's estimate of biomass over time. In concordance with the weight-estimate method, data is collected by using defined weight-units for each species to visually estimate the biomass in each quadrant. However, a small second calibration data set is also collected, by clipping and weighing selected quadrants after estimation. Regression analysis is used to compare estimated and harvested values of the calibration samples, to determine if tended to underestimate or overestimate the visual estimation, and to provide the appropriate adjustments to be made to all field samples.
The number of samples selected for the calibration data set depends on the observer's ability to furnish accurate visual estimates, the sample variance of biomass estimates, the diversity of species on the site, and time restrictions. Ideally, calibration data should encompass the range of biomass values and the majority of species encountered during sampling. Fewer calibration samples are needed when the observer's visual estimates closely reflect harvested weights. However, the observer's proficiency cannot be confirmed until after the calibration quadrants are clipped and weighed! Clipping one out of every 5 - 10 quadrants for inclusion in the calibration data set provides a reliable calibration in most situations.
Data is usually collected form multiple quadrants located along a transect, so that the transect is the sample unit. Therefore, data must be collected from several transects to determine the precision of the sample, for statistical analysis of biomass data.
