The following variables have the following significant relationships (x is the explanatory variable): linear, cubic, exponential, logistic. The linear relationship plots without any trouble. 

Cubic is the 'best' model, but it is not plotting as a smooth curve using the following code:

cubic.lm<- lm(y~poly(x,3))
lines(x,predict(cubic.lm),lwd=2)

How do I plot the data and the estimated curves for all of these regression models in the same plot? 

x <- c(62.5,68.5,0,52,0,52,0,52,23.5,86,0,0,0,0,0,0,0,0,0,0)

y <- c(0.054,0.055,0.017,0.021,0.020,0.028,0.032,0.073,0.076,0.087,0.042,0.042,0.041,0.045,0.021,0.018,0.017,0.018,0.028,0.022)

Thanks in advance.

Rhonda Reidy

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