R help - Jan 2012 - What does the : operator mean in glm formulas

Hi,

I see the following is the credit scoreing in R guide :

m2<-glm(formula = good_bad ~ checking + duration + history+ purpose +amount +
savings + employed + installp + marital +
coapp +age + other + depends + telephon + foreign +checking:amount

What does checking:amount mean?

Regards,

Xiaobo Gu

On 19-Jan-2012 Xiaobo Gu wrote:
> Hi,
> I see the following is the credit scoreing in R guide :
> 
> m2<-glm(formula = good_bad ~ checking + duration + history +
> purpose +amount + savings + employed + installp + marital +
> coapp +age + other + depends + telephon + foreign +checking:amount
> 
> What does checking:amount mean?
> 
> Regards,
> Xiaobo Gu
See the explanation of model formulae under "Details" in ?glm :

  A specification of the form ?first:second? indicates
  the set of terms obtained by taking the interactions
  of all terms in 'first' with all terms in 'second'.
  The specification 'first*second' indicates the _cross_
  of 'first' and 'second'.
  This is the same as 'first + second + first:second'.

Ted.

-------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
Date: 19-Jan-2012  Time: 13:37:23
This message was sent by XFMail

On Jan 19, 2012, at 8:02 AM, Xiaobo Gu wrote:
> Hi,
>
> I see the following is the credit scoreing in R guide :
>
> m2<-glm(formula = good_bad ~ checking + duration + history+ purpose  
> +amount + savings + employed + installp + marital +
> coapp +age + other + depends + telephon + foreign +checking:amount
>
> What does checking:amount mean?
?formula

-- 

David Winsemius, MD
West Hartford, CT

>Such a model consists of a series of terms separated by +operators. 
In the above ,term means individual variable.
>The terms themselves consist of variable and factor names separated by :
operators.
What does term mean in this?
>Such a term is interpreted as the interaction of all the variables and
factors appearing in the term.
What does interaction mean, and what does term mean here ?






Xiaobo Gu

From: David Winsemius
Date: 2012-01-19 21:46
To: guxiaobo1982
CC: r-help; ds5j
Subject: Re: [R] What does the : operator mean in glm formulas

On Jan 19, 2012, at 8:02 AM, Xiaobo Gu wrote:
> Hi,
>
> I see the following is the credit scoreing in R guide :
>
> m2<-glm(formula = good_bad ~ checking + duration + history+ purpose  
> +amount + savings + employed + installp + marital +
> coapp +age + other + depends + telephon + foreign +checking:amount
>
> What does checking:amount mean?
?formula

-- 

David Winsemius, MD
West Hartford, CT