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3.8.1.2 Support for the Difference Score Method
Although the difference scores have met with some criticism, numerous researchers
still support this method (e.g. Rogosa, Brandt, & Zimowski, 1982; Rogosa & Willett,
1983; Tisak & Smith, 1994). These researchers accept that the reliability of a
difference score may be less than the average reliability of its components, if these
components are positively correlated and equal if the correlation is zero. Tisak and
Smith (1994) observe that the presumed unreliability has arisen because the component
variables are predominantly positively correlated and that, if the components are
reliable but not highly positively correlated, then their difference score reliability could
be accepted. Their study concludes that the difference scores are not completely
unreliable and reliability may be increased by increasing the number of items. Their
research further states that the issues concerned with the validity of difference scores
should be viewed in the context of the study questions. Some researchers believe that
the difference score techniques could be used if the study questions focus on only the
differences and not on the relative effects of its component variables (e.g. Rogosa et
al., 1982; Rogosa & Willett, 1983; Tisak & Smith, 1994).
From this discussion it is perceived that there are two schools of thought regarding the
use of the difference scores. While one school contrasts a simple model against a
greater response surface model, the other suggests that alternate models to difference
scores first need to be evaluated (Tisak & Smith, 1994). This research focuses on the
relationship of the LMX agreement to the employee’s organisational attitudes and not
on the individual contribution of the supervisor and the subordinate (component
variables) to the agreement. As a result this research uses the difference score
technique to convert and collapse both supervisor and subordinate LMX variables into
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