pesticideTrendCalcs {seawaveQ}

Summarize linear trends

Description

Internal function to summarize the trend results.

Usage

pesticideTrendCalcs(
  tndbeg,
  tndend,
  ctnd,
  pval,
  alpha,
  setnd,
  scl,
  baseConc,
  mclass
)

Arguments

tndbeg

is the beginning (in whole or decimal years) of the trend period. Zero means the begin date will be the beginning of the concentration data, cdat.

tndend

is the end of the trend (treated as December 31 of that year). Zero means the end date will be the end of the concentration data, cdat.

ctnd

is the concentration trend, the coefficient on the time variable.

pval

is the p-value for the linear trend component.

alpha

is the significance level or alpha value for statistical significance and confidence intervals.

setnd

is the standard error for the linear trend component.

scl

is the scale factor from the survreg.object.

baseConc

is the base concentration, the median concentration (midpoint of the trend line) for the first year of the trend analysis .

mclass

indicates the class of model to use. A class 1 model is the the traditional SEAWAVE-Q model that has a linear time trend. A class 2 model is a newer option for longer trend periods that uses a set of restricted cubic splines on the time variable to provide a more flexible model.

Format

The data frame returned has one row for each chemical analyzed and the number of columns are defined as follows:

pname	character	parameter analyzed
mclass	numeric	a value of 1 or 2
alpha	numeric	a significance level
ctndPpor	numeric	the concentration trend in percent over the period of record
cuciPpor	numeric	the concentration upper confidence interval for the trend in
		percent over the period of record
clciPpor	numeric	the concentration lower confidence interval for the trend in
		percent over the period of record
baseConc	numeric	the base concentration, median concentration or midpoint of
		trend line, for first year of trend period
ctndOrigPORPercentBase	numeric	the concentration trend in original units over
		the period of record
		(calculation based on percent per year and base concentration)
cuciOrigPORPercentBase	numeric	the concentration trend upper confidence interval
		for the trend in original units over the period of record
		(calculation based on percent per year and base concentration)
clciOrigPORPercentBase	numeric	the concentration trend lower confidence interval
		for the trend in original units over the period of record
		(calculation based on percent per year and base concentration)
ctndlklhd	numeric	is the concentration trend likelihood

Details

pesticideTrendCalcs is called from within fitswavecav

Value

The data frame returned has one row for each chemical analyzed and summaries of the trend.

Note

Based on trend calculations used to display and summarize pesticide trends here https://nawqatrends.wim.usgs.gov/swtrends/. A likelihood value that is the functional equivalent of the two-sided p-value associated with the significance level of the trend was determined as follows: Likelihood = (1 - (p-value / 2)), where p-value is the p-value for the trend coefficient (Oelsner and others, 2017).

Author(s)

Karen R. Ryberg

References

Oelsner, G.P., Sprague, L.A., Murphy, J.C., Zuellig, R.E., Johnson, H.M., Ryberg, K.R., Falcone, J.A., Stets, E.G., Vecchia, A.V., Riskin, M.L., De Cicco, L.A., Mills, T.J., and Farmer, W.H., 2017, Water-quality trends in the Nation's rivers and streams, 1972–2012—Data preparation, statistical methods, and trend results (ver. 2.0, October 2017): U.S. Geological Survey Scientific Investigations Report 2017–5006, 136 p., https://doi.org/10.3133/sir20175006.