IsoplotR (version 0.6)

weightedmean: Calculate the weighted mean age

Description

Models the data as a Normal distribution with two sources of variance. Estimates the mean and 'overdispersion' using the method of Maximum Likelihood. Computes the MSWD of a Normal fit without overdispersion. Implements Chauvenet's Criterion to detect and reject outliers.

Usage

weightedmean(x, ...)
"weightedmean"(x, detect.outliers = TRUE, plot = TRUE, rect.col = rgb(0, 1, 0, 0.5), outlier.col = rgb(0, 1, 1, 0.5), sigdig = 2, alpha = 0.05, ...)
"weightedmean"(x, detect.outliers = TRUE, plot = TRUE, rect.col = rgb(0, 1, 0, 0.5), outlier.col = rgb(0, 1, 1, 0.5), sigdig = 2, type = 4, cutoff.76 = 1100, cutoff.disc = c(-15, 5), alpha = 0.05, dcu = TRUE, ...)
"weightedmean"(x, detect.outliers = TRUE, plot = TRUE, rect.col = rgb(0, 1, 0, 0.5), outlier.col = rgb(0, 1, 1, 0.5), sigdig = 2, alpha = 0.05, dcu = TRUE, ...)

Arguments

x

a two column matrix of values (first column) and their standard errors (second column) OR an object of class UPb OR an object of class ArAr

...

optional arguments

detect.outliers

Boolean flag indicating whether outliers should be detected and rejected using Chauvenet's Criterion.

plot

Boolean flag indicating whether the function should produce graphical output or return numerical values to the user.

rect.col

the fill colour of the rectangles used to show the measurements or age estimates.

outlier.col

if detect.outliers=TRUE, the outliers are given a different colour.

sigdig

the number of significant digits of the numerical values reported in the title of the graphical output.

alpha

the confidence limits of the error bars/rectangles.

type

scalar indicating whether to plot the $^{207}$Pb/$^{235}$U age (type=1), the $^{206}$Pb/$^{238}$U age (type=2), the $^{207}$Pb/$^{206}$Pb age (type=3), the $^{207}$Pb/$^{206}$Pb-$^{206}$Pb/$^{238}$U age (type=4), or the (Wetherill) concordia age (type=5)

cutoff.76

the age (in Ma) below which the $^{206}$Pb/$^{238}$U and above which the $^{207}$Pb/$^{206}$Pb age is used. This parameter is only used if type=4.

cutoff.disc

two element vector with the maximum and minimum percentage discordance allowed between the $^{207}$Pb/$^{235}$U and $^{206}$Pb/$^{238}$U age (if $^{206}$Pb/$^{238}$U < cutoff.76) or between the $^{206}$Pb/$^{238}$U and $^{207}$Pb/$^{206}$Pb age (if $^{206}$Pb/$^{238}$U > cutoff.76). Set cutoff.disc=NA if you do not want to use this filter.

dcu

propagate decay constant uncertainty?

Value

if PLOT=FALSE, returns a list with the follwing items:mean: a two element vector with the weighted mean and its standard error.disp: a two element vector with the (over)dispersion and its standard error.mswd: the Mean Square of the Weighted Deviates (a.k.a. `reduced Chi-square' statistic)p.value: the p-value of a Chi-square test with n-1 degrees of freedom, testing the null hypothesis that the underlying population is not overdispersed.valid: vector of Boolean flags indicating which steps are included into the weighted mean calculation

Examples

ages <- c(251.9,251.59,251.47,251.35,251.1,251.04,250.79,250.73,251.22,228.43)
errs <- c(0.28,0.28,0.63,0.34,0.28,0.63,0.28,0.4,0.28,0.33)
weightedmean(cbind(ages,errs))
#data(examples)
#weightedmean(examples$ArAr)