loess line not plotting correctly

Question

I'm having trouble fitting a loess smooth plus confidence limits to a scatterplot of residuals. My model is height ~ weight + chest circumference. To check linearity of chest circumference, I've fitted a model without chest circumference (i.e. height ~ weight), and plotted the residuals of this model against chest circumference. So far so good. I then tried to use `loess()` and `predict()` to plot a loess line, plus confidence limits. The result looks like this (in the picture I've only plotted the central line, but the CI lines look the same): Loess problem in scatterplot The points are correct (when I plot the loess fit as points it looks right), but for some reason the line is not being drawn how I expect. My code is below: ``` # bf.red = data set; mod.nch = model; chestc = chest circumference; # loess = loess model; lo.pred = predict loess plot(bf.red$chestc #Chest circumference ,residuals(mod.nch)) #Residuals from height ~ weight model loess <- loess(mod.nch$residuals ~ bf.red$ch…

Accepted Answer

`lines` connects the points in the order in which they appear, which is sometimes undesirable. You can sort them as follows:

```
i <- order(bf.red$chestc)
lines(bf.red$chestc[i], lo.pred$fit[i])
...
```

loess line not plotting correctly

Solution

Problem