# nonLinearC: Confidence intervals for crossover points using non-linear... In crossReg: Confidence intervals for crossover points of two simple regression lines

## Description

Calculate confidence intervals for crossover points of two simple linear regression lines using non-linear regression.

## Usage

 `1` ```nonLinearC(Data, startingValue) ```

## Arguments

 `Data` a dataframe containing data values for y, x1, and x2 `startingValue` a list containing starting values for estimating parameters in non-linear regression

## Details

For a crossover point C = -b2/b3 of the two simple regression lines, Widaman et al. (2012) proposed to estimate C using the non-linear regression of the form y = A0 + A1*(x1-C) + A2*(x1-C)*x2. The function nonLinearC() estimates C using the non-linear regression and calculates the confidence intervals for C based on the standard error of C obtained from a non-linear regression.

## Value

 `C_Hat` estimate of C from a non-linear regression `SE` standard error of C from a non-linear regression `LowCI` lower bound of confidence intervals for C based on a non-linear regression `UpperCI` upper bound of confidence intervals for C based on a non-linear regression

Sunbok Lee

## References

Aiken, L. S., & West, S. G. (1991). Multiple regression: Testing and interpreting interactions. Newbury Park, CA: Sage

Widaman, K. F., Helm, J. L., Castro-Schilo, L., Pluess, M., Stallings, M. C., & Belsky, J. (2012). Distinguishing ordinal and disordinal interactions. Psychological Methods, 17, 615-622

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14``` ```# set initial values for non-linear regression startingValue <- list(A0 = 1, B1 = 1, B2 = 1, C = 1) # example data library(MASS) out <- mvrnorm(1000, mu = c(0,0), Sigma = matrix(c(1,0.2,0.2,1), ncol = 2),empirical = TRUE) x1 <- out[,1] x2 <- out[,2] epsilon <-rnorm(1000,0,1) y <- 1 + 1*x1 + 0.5*x2 + 1*x1*x2 + epsilon # true C = -0.5/1 = -0.5 simData <- data.frame(y=y,x1=x1,x2=x2) # run nonLinearC() nonLinearC(simData, startingValue) ```

crossReg documentation built on May 30, 2017, 5:25 a.m.