In fact, one well-known psychometrician, Paul Kline
(recently-deceased) has been fairly scathing about locus of
control. In "Personality: The psychometric view" (1993) he
says: "It is clear that there is no common factor of locus
of control. Whatever is measured by these items is largely
composed of variance in other tests, especially
neuroticism, psychoticism and social desirability".
Locus of control fails to predict beliefs in specific
fields. E.g. it does not predict health beliefs, and for
this reason there is a specific Health Locus of Control
measure.
David Hardman
On Fri, 10 Dec 1999 17:22:04 GMT [EMAIL PROTECTED]
wrote:
> You might like my reply.
>
> Even with a low Alpha, the sum of the items is still a better measure
> of the trait (locus of control) than any individual item. This assumes
> that the items have 'face validity' as measures of locus of control.
> It also assumes that whatever they do have in common is mainly the
> locus-of-control trait (rather than, say, some other thing like social
> desirability).
>
> If so, then the only real 'problem' is that your summed score is a
> relatively weak measure of locus of control. (That is, it has limited
> validity--i.e., the correlation of the score with the true
> trait--because reliability constrains the level of validity). But that
> means any statistical analysis you perform is *conservative*. That is,
> by using a weak measure of locus of control, you are 'stacking the
> deck' against finding a significant relationship between locus of
> control with the other variables in your study. Now, if you have
> obtained statistically significant results with a weak measure of locus
> of control, then your results are still significant! In fact, one
> could argue that they are even stronger since you have obtained
> significant results with the deck stacked against finding them.
>
> This principle is frequently overlooked. Ultimately, a scale only has
> to be as reliable as you need to find statistically significant results
> when comparing the scale with another construct.
>
> So, to summarize, if you have obtained significant results with your
> summed score, you can go back to your critics with confidence and point
> out that you have done so with a conservative analysis, and that had
> you used a more 'reliable' scale, your results would only be stronger.
>
> Naturally this assumes you have obtained positive results. If you have
> obtained negative results (lack of correlation between the scale and
> some other variable(s)), then clearly this logic does not apply.
>
> One other thing to mention: one could set up the problem as a
> LISREL-type model, in which the four items are multiple indicators of a
> common trait (locus of control.) Interestingly, in a
> multiple-indicator type model, people rarely bring up the issue of the
> reliability of the common trait and how it is influenced by the number
> of indicators, although, logically, one would think it would apply more
> as less in the same way as adding the items to create an aggregate
> score. This isn't to suggest that you do a LISREL analysis--it's
> merely to point out a logical inconsistency in how people regard
> multiple indicators.
>
> John Uebersax
> [EMAIL PROTECTED]
>
> In article <AC09DC4F4DFCD211A83C00805FE6138D3691B9@NHQJPK1EX2>,
> [EMAIL PROTECTED] (Magill, Brett) wrote:
>
> > Just wanted people's thought on the following:
> >
> > I am a graduate student in sociology studying individual's
> perceptions of
> > control (locus of control) using existing data. The data set include
> four
> > items to measure this construct which were taken from a larger scale
> of more
> > than twenty, the larger scale reaching an acceptable level of
> reliability (I
> > do not know the exact level, but it is a widely researched and used
> > instrument) in previous research. The four items that were included
> were
> > selected as the best measures of the construct based on empirical
> evidence
> > (item-total correlation's, factor analysis).
> >
> > In my own research, I used these items and decided to sum responses
> across
> > these four likert-type items. However, the Alpha reliability is very
> low
> > 0.30 (items were reverse scored as necessary and coding was
> double-checked).
> > I defended the decision to sum the items, despite the low Alpha,
> based on
> > the fact that they were selected from a larger set of items which are
> > internally consistent. In presenting my findings, I was heavily
> criticized
> > for this decision.
>
>
>
> Sent via Deja.com http://www.deja.com/
> Before you buy.
Dr. David Hardman
"Calamities are of two kinds: misfortune to
ourselves, and good fortune to others." - Ambrose Bierce
Phone: +44 0171 3201256
Fax: +44 0171 3201236
E-mail: [EMAIL PROTECTED]
Internet: http://www.lgu.ac.uk/psychology/hardman.html
For information on the London Judgment and Decision Making Group
visit: http://www.lgu.ac.uk/psychology/hardman/ljdm.html
