Re: st: RE: Mean test in a Likert Scale

["Seed, Paul" <paul.seed@kcl.ac.uk>]

Dear Statalist, 

I sympathise with everything Nick has said.

But there is a further point to be considered here:
It is sometimes argued on psychometric grounds that 
when people answer a question on a Likert scale, there are two 
processes - firstly the answer (Yes/No)
secondly a personal preference (or avoidance) of extreme views
(what is sometimes called "response style").

So mild-mannered Clark Kent may always give answers as 2 or 4,
while Superman, the man of steel prefers 1 or 5.  But their 
meaning is the same. (Or compare mild-mannered Chinese students 
with more forthright Americans).

If so, and assuming you want to catch the answer & drop the personal preference;
it makes sense to collapse the Likert scale to 2 or 3 points (possibly treating 
3 as separate from 4 and 5).
But that depends on the question "Do people really behave like this?"

Googling "collapse Likert scale response style" turned up some relevant references, which I have not read.


Leonor Saravia <lmisaravia@gmail.com> wrote: 

Dear Nick and David,

I really appreciate your reply, thank you.

I read carefully your answers to my questions and as Nick says, my
first question pointed to the fact that there could be the sense in
which computing the mean score of a Likert scale is allowed. I have
seen practical studies were the mean of this kind of scales are
calculated and interpreted. However, there is also literature that
indicates that, as the Likert scales are an ordinal-level measure, you
should not calculate the mean of it. So, I am confused because I do
not understand whether calculating and interpreting the mean of a
Likert scale is correct or not.

The data I have is disaggregated by individual (20000 observations) of
a treatment and a control group, and has the answer for each of the 26
questions, a number between 1 and 5, which are the values of a 5 point
Likert scale from Disagree (1) to Agree (5).

For instance, the first question (Q1) is: "Chilean people find
entrepreneurial activities socially valuable" and the possible answers
are:

1 - Strongly disagree
2 - Disagree
3 - Nor agree nor disagree
4 - Agree
5 - Strongly agree

So, the database has this structure:

Observation     Group            Q1  Q2  .....  Q25  Q26
1                     Treatment      1     5   ......   3      1
2                     Control           3    1   .......  2      5
.
.
19999             Control          5     2  ........ 4       3
20000             Treatment      3     2  ......... 5      4