Charlotte Manly wrote: (in response to my query...)
> If that scale is well-constructed, it _is_ an interval scale
> (or awfully close to one). Measurement issues are beyond my
> area of expertise, but as I understand it, if you only label
> the endpoints, subjects tend to treat it as an interval
> scale. If you carefully label each code number (and can show
> that subjects perceive each label as about equally far from
> its neighbors) then it's also an interval scale. On the
> other hand, if your labels are something like, "never,"
> "almost never," "pretty often," and "always," you'll have a
> hard time arguing that that's an interval scale.
Thanks for the comments. I should have been more clear. I'm aware
that if the scale is the result of careful scale construction, the result is
a genuinely interval scale (or close enough for jazz...). I meant to direct
my question to "scales" (I hesitate to use the term for these as it begs the
question to some degree) for which that scale construction was NOT done.
That is, I meant to ask about the kind of thing that you referred to in the
last sentence of your reply.
I have _always_ believed that one can treat carefully constructed
scales (e.g., the product of the Thurstone technique) as interval. Is it
also true that we can do so for the kind of "thrown-together scales" we (or
our students) so often use?
Paul Smith
Alverno College
Milwaukee
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