poly_smth1: Fit a polynomial to demographic data

In timriffe/DemoTools: Standardize, Evaluate, and Adjust Demographic Data

Fit a polynomial to demographic data

Description

Smooth data over age fitting linear models, preserving the open age group if necessary. This is a wrapper to stats::lm() but using standard demographic arguments.

Usage

poly_smth1(Value, Age, degree = 2, trans, pow = 2, OAG = TRUE, ...)

Arguments

Value	numeric vector of counts in single, abridged, or 5-year age groups.
Age	integer vector of ages corresponding to the lower integer bound of the counts.
degree	integer degree of polynomial. Default 2.
trans	if a transformation is desired, either specify "log" or "power", otherwise leave missing.
pow	if "power" specified for trans then the power transformation to apply.
OAG	logical. Whether or not the top age group is open. Default TRUE.
...	optional arguments passed to stats::lm()

Details

The total sum of Value is preserved in the output. One can control smoothness by adjusting the degree of the polynomial (higher degree more wiggly). See lm for more details. One may wish to log transform the data before fitting the polynomial, in which case trans should be specified as "log". "power" is also an option in which case the data is transformed by Value^(1/pow) before fitting, and then the prediction is back-transformed (negative values not allowed)– This is friendlier in the case of 0s. For the log transformation, 0s have no weight.

See Also

lm

Examples

## Not run: 
Age <- 0:99
cols <- RColorBrewer::brewer.pal(7,"Reds")[3:7]
plot(Age,pop1m_pasex)
lines(Age, poly_smth1(pop1m_pasex, Age, OAG = FALSE),col=cols[1])
lines(Age, poly_smth1(pop1m_pasex, Age, degree = 3, OAG = FALSE), col = cols[2])
lines(Age, poly_smth1(pop1m_pasex, Age, degree = 3, trans = "log", OAG = FALSE), col = cols[3])
lines(Age, poly_smth1(pop1m_pasex, Age, degree = 3,
      trans = "power", pow = 2, OAG = FALSE), col = cols[4])
lines(Age, poly_smth1(pop1m_pasex, Age, degree = 4,
      trans = "power", pow = 3, OAG = FALSE), col = cols[5])

## End(Not run)

timriffe/DemoTools documentation built on Oct. 14, 2024, 12:53 p.m.