R help - Sep 2016 - What are the red line and cut line in lm's Residuals vs Fitted plot?

What are the red line and cut line in lm's Residuals vs Fitted plot?

As seen in e.g.:

http://i.imgur.com/QvZ6oeT.png

> On Sep 18, 2016, at 7:25 AM, mviljamaa <mviljamaa at kapsi.fi> wrote:
> 
> What are the red line and cut line in lm's Residuals vs Fitted plot?
> 
> As seen in e.g.:
> 
> http://i.imgur.com/QvZ6oeT.png
R has a `plot.lm` function that is invoked by `plot(lm_object)` when `lm_object`
has a class of "lm". It produces multiple diagnostic plots. The
default is for display of 4 of the possible 6 plots.

The help page can be specifically accessed by:

?plot.lm

And run the first example:

lm.SR <- lm(sr ~ pop15 + pop75 + dpi + ddpi, data = LifeCycleSavings)
plot(lm.SR)


If you have further question about that particular plot, which would be the
first one, you should first review the help page and then review the code seen
with:

plot.lm
#Error: object 'plot.lm' not found
getAnywhere(plot.lm)  # the way to see code that is not exported:

See:

function (x, which = c(1L:3L, 5L), caption = list("Residuals vs
Fitted",
    "Normal Q-Q", "Scale-Location", "Cook's
distance", "Residuals vs Leverage",
    expression("Cook's dist vs Leverage  " * h[ii]/(1 - h[ii]))), 
    panel = if (add.smooth) panel.smooth else points, sub.caption = NULL, 
    main = "", ask = prod(par("mfcol")) < length(which)
&& dev.interactive(),
    ..., id.n = 3, labels.id = names(residuals(x)), cex.id = 0.75, 
    qqline = TRUE, cook.levels = c(0.5, 1), add.smooth =
getOption("add.smooth"),
    label.pos = c(4, 2), cex.caption = 1, cex.oma.main = 1.25) 


Note: I checked the option setting with:
> getOption("add.smooth")
[1] TRUE

---snipped plotting set up logic -----

if (show[1L]) {
        ylim <- range(r, na.rm = TRUE)
        if (id.n > 0) 
            ylim <- extendrange(r = ylim, f = 0.08)
        dev.hold()
        plot(yh, r, xlab = l.fit, ylab = "Residuals", main = main, 
            ylim = ylim, type = "n", ...)
        panel(yh, r, ...)   # this is what is drawing the "red line"
        if (one.fig) 
            title(sub = sub.caption, ...)
        mtext(getCaption(1), 3, 0.25, cex = cex.caption)
        if (id.n > 0) {
            y.id <- r[show.r]
            y.id[y.id < 0] <- y.id[y.id < 0] - strheight("
")/3
            text.id(yh[show.r], y.id, show.r)
        }
        abline(h = 0, lty = 3, col = "gray")  # this is drawing the
dotted line
        dev.flush()


So the `panel` function is creating the "red line" and its help page
is at:

?panel.smooth   #...

... since the `panel funciton was given that value.

-- 
David.
> 
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David Winsemius
Alameda, CA, USA

> What are the red line and cut line in lm's Residuals vs Fitted plot?
The dotted line is at 0 and the red line is a locally weighted regression
calculated using lowess and plotted using panel.smooth.

See ?panel.smooth and ?lowess for details

The main clue to this is in the arguments to ?plot.lm, which uses panel.smooth
as a panel function.

S Ellison



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Do you mean that the red line is a regression line?
Why is the regression (line) weighted?

On 2016-09-19 14:41, S Ellison wrote:
>> What are the red line and cut line in lm's Residuals vs Fitted
plot?
> The dotted line is at 0 and the red line is a locally weighted
> regression calculated using lowess and plotted using panel.smooth.
> 
> See ?panel.smooth and ?lowess for details
> 
> The main clue to this is in the arguments to ?plot.lm, which uses
> panel.smooth as a panel function.
> 
> S Ellison
> 
> 
> 
> *******************************************************************
> This email and any attachments are confidential. Any u...{{dropped:8}}