Re: st: 1-4 scale

[David Hoaglin <dchoaglin@gmail.com>]

Dear Ebru,

In that -generate- command, you are using the mean as the "centering
constant."  If you want to use a different constant, say 3, the
command would go

gen centered_var1 = var1 - 3

Centering at the mean often has useful properties, but it is not
always the most effective choice.

David Hoaglin

On Sun, Aug 5, 2012 at 12:18 PM, Ebru Ozturk <ebru_0512@hotmail.com> wrote:
> Dear David,
>
> Is this command below right to center a variable? If it is right, where do I use "the centering constant"?
>
> sum var1
> gen centered_var1 = var1 - r(mean)
>
> Ebru
>
> ----------------------------------------
>> Date: Sun, 5 Aug 2012 11:57:40 -0400
>> Subject: Re: st: 1-4 scale
>> From: dchoaglin@gmail.com
>> To: statalist@hsphsun2.harvard.edu
>>
>> Dear Ebru,
>>
>> People often analyze data from Likert scales as equally spaced, so you
>> can use each of the eight items in your model as a numerical variable,
>> with values 1 to 4. You simply need to be aware that you are treating
>> the four categories as equally spaced.
>>
>> Earlier you asked about centering those variables. Centering will do
>> no harm. As far as the model is concerned, it affects only the
>> definition of the intercept. If you do decide to "center" the
>> variables, you may want to use one of the four values. If the data on
>> an item are not concentrated at one end, you could use 2 or 3 or
>> perhaps 2.5 as the centering constant. (In a 5-point Likert scale
>> with a neutral category at 3, using 3 would often be a reasonable
>> choice.)
>>
>> When you have the results from the model with the eight separate
>> items, you may want to see whether the coefficients for the four items
>> within a heading are similar. If they are, and it makes sense, you
>> could consider replacing those four items with their sum (or average)
>> --- a composite score.
>>
>> David Hoaglin
>>
>> On Sun, Aug 5, 2012 at 2:35 AM, Ebru Ozturk <ebru_0512@hotmail.com> wrote:
>> > Dear David,
>> >
>> > I use tobit estimation. If I enter each item (8) in the question (objectives of innovation) into the model without changing their values, leaving them as they are (1 to 4), does it work? Because sometimes tobit can create problems if it has many variables in the model.
>>
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