R help - Sep 2013 - question about "lines"

Hi all:
I met a question about "lines".


attach(cars)


plot(dist ~ speed)
#add the regression line to the plot
lines(fitted(lm(dist~speed)) ~ speed)


plot(dist ~ speed)
#what kind of curve does the following command add to the plot?
lines(fitted(lm(dist~speed)))


My question is :
what kind of curve does the last command add to the plot?


My guess:maybe the level of fitted values?
> range(fitted(lm(dist~speed)))
[1] -1.84946 80.73112


But from the plot,I can see the range of the curve is about 10 to 40 more or
less,which is different from(-1.84946, 80.73112).So the curve must not be the
fitted values.What kind of curve does the last command add to the plot then?




Many thanks for your help


My best
	[[alternative HTML version deleted]]

Dear
 meng,

Re:
> Hi all:
> I met a question about "lines".
> 
> 
> attach(cars)
> 
> 
> plot(dist ~ speed)
> #add the regression line to the plot
> lines(fitted(lm(dist~speed)) ~ speed)
> 
> 
> plot(dist ~ speed)
> #what kind of curve does the following command add to the plot?
> lines(fitted(lm(dist~speed)))
(etc..)




I guess you need the function abline(), not lines() to add a regression line.
Hoping this helps, I remain,
With best wishes,


Franklin
--



Dr. Franklin Bretschneider
Dept of Biology
Utrecht Unversity
Padualaan 8
3584 CH  Utrecht
The Netherlands
f.bretschneider@uu.nl



	[[alternative HTML version deleted]]

On 13-09-17 8:06 AM, meng wrote:
> Hi all:
> I met a question about "lines".
>
>
> attach(cars)
>
>
> plot(dist ~ speed)
> #add the regression line to the plot
> lines(fitted(lm(dist~speed)) ~ speed)
>
>
> plot(dist ~ speed)
> #what kind of curve does the following command add to the plot?
> lines(fitted(lm(dist~speed)))
>
>
> My question is :
> what kind of curve does the last command add to the plot?
Look at the class of fitted(lm(...)).  It is "numeric".  So what
you're
seeing is the same as if you computed the fitted values, and then did

lines(values)

Since values is just a vector of numbers, that will plot them as y 
values against x values 1:length(values).  That's unlikely to be a 
useful thing to do.

Duncan Murdoch
>
>
> My guess:maybe the level of fitted values?
>> range(fitted(lm(dist~speed)))
> [1] -1.84946 80.73112
>
>
> But from the plot,I can see the range of the curve is about 10 to 40 more
or less,which is different from(-1.84946, 80.73112).So the curve must not be the
fitted values.What kind of curve does the last command add to the plot then?
>
>
>
>
> Many thanks for your help
>
>
> My best
> 	[[alternative HTML version deleted]]
>
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