Resistant line or Tukey line

Most elements explained here applied to regression-type functions; please read it as an introduction to these functions.

line() produces a Tukey line>

`line(urb,infmor)`

When you execute this command line, you will see this output that contains the regression coefficients.

```Call:
line(x, y)

Coefficients:
[1]  60.5868  -0.1157
```

You can also store the object:

```resline =  line(urb,infmor)
```

an then examine this object with str(resline) to display:

```List of 4
\$ call         : language line(x, y)
\$ coefficients : num [1:2] 60.587 -0.116
\$ residuals    : num [1:183] -42.47  -2.36 -24.24 -12.12  29.99 ...
\$ fitted.values: num [1:183] 60.5 60.4 60.2 60.1 60.0 ...
- attr(*, "class")= chr "tukeyline"
```

The function creates an object of type "tukeyline" which is a regression type object; a series of functions let you extract this information from it for their specific purpose.

• coef(resline) Slope and the intercept
• fitted(resline)Fitted values
• residuals(resline)Residuals

The same information can also be retrieved using resline\$coefficients, resline\$residuals or resline\$fitted.

You can use this directly in various functions, e.g.

• abline(resline\$coefficients) (abline(resline) is also ok ) adds the resistant line to the current plot.
• plot(resline\$residuals) produces a residual plot
• plot(residuals(resline) ~ fitted(resline)) plots the residuals against the fitted values.

Note that you can also write: plot(line(urb~infmor)\$residuals))