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Table 5.5: NTP Instrument rating scale analysis

Difference Distance between Justification for merging or retaining the scale
between categories
categories (Andrich threshold)

2 – 3 0 - (-4.04) = 4.04 Scales 2, 3, 4 and 5 were retained because the
3 – 4 -4.04 - (-0.17) = 3.87 distances between categories were in the range of 1.4
logit to 5.00 logit.
4 – 5 -0.17 - (4.21) = 4.38
Nevertheless, the use of 5-point Likert scale would be maintained in this
instrument because previous studies have found that the validity and
reliability of instruments with a 5- to 7-point Likert scale were better than
the use of fewer scales (Dawes, 2008). Linacre (2002) also explains that
not all review criteria are relevant for all the data but the criteria provide
a useful measure in conducting rating scale analysis.

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