Interaction between variables

library(ggplot2)

XLineA <- runif(numbervalues, 0, 20);          # Simulates X-data 0 - 20,
XLineB <- runif(numbervalues, 0, 20);          # from uniform distribution.
    
YLineA <- LineA_B0 + LineA_B1*XLineA + LineA_B2*XLineA*XLineA + rnorm(numbervalues, 0, standres)
YLineB <- LineB_B0 + LineB_B1*XLineB + LineB_B2*XLineB*XLineB + rnorm(numbervalues, 0, standres)

type  = rep(c("A", "B"), each = numbervalues)
    
Ytot <- c(YLineA, YLineB)                  # All Y-data.
Xtot <- c(XLineA, XLineB)                  # All X-data.
    
myData <- data.frame(Ytot, Xtot, type)
         
model <- lm(Ytot ~ (Xtot + I(Xtot*Xtot))*type )

summary(model)                                         # Shows result from analysis.
residuals <- resid(model)                              # Shows the residuals.
myData['Residuals'] <- residuals                       # Includes residuals into data frame.
   
mat_coeff <- summary(model)$coefficients               # All estimated coefficients.

b0 <- mat_coeff[1, 1]   # (Intercept)                  # Extracts coefficients.
b1 <- mat_coeff[2, 1]   # X
b2 <- mat_coeff[3, 1]   # X2
b3 <- mat_coeff[4, 1]   # typeB
b4 <- mat_coeff[5, 1]   # X:typeB
b5 <- mat_coeff[6, 1]   # X2:typeB 
 
b0A <- b0                                              # ESTIMATED intercept and slope (red)
b1A <- b1
b2A <- b2

b0B <- b0 + b3                                         # ESTIMATED intercept and slope (blue)
b1B <- b1 + b4
b2B <- b2 + b5

ymax = max(1.05*Ytot)                                  # Stretches the Y-axis.
ymin = min(Ytot)

fun1 <- function(XLineA) b0A + b1A*XLineA + b2A*XLineA*XLineA 
fun2 <- function(XLineB) b0B + b1B*XLineB + b2B*XLineB*XLineB

myDiagram <- ggplot(myData, aes(x = Xtot, y = Ytot)) +
  annotate("text", x=10.0, y=ymax, label="Estimated models", fontface="bold", color="blue", size=6) + 
  geom_point(colour=rep(c("red","blue"), each=numbervalues)) + ylim(ymin, ymax)
  
myDiagram <- myDiagram + stat_function(fun = fun1, color="red")              # Adds line (A)
myDiagram <- myDiagram + stat_function(fun = fun2, color="blue")             # Adds line (B)
myDiagram

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Interaction between variables

A linear model with two groups and one X-variable

The data column consists of two groups,
possibly from different models

Här skall skrivas infotext.

Data consists of two groups (A) and
(B) generated by the models:

β₀

β₁

β₂

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