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Validity
It involves accumulating evidence from different forms.
Content Validity—Extent to which the content (items) of a scale is representative of
the conceptual construct it is intended to measure.
• Consideration of item sufficiency and the target population.
• Clearly defined construct.
• Qualitative evidence from individuals for whom the measure is targeted, expert
opinion and literature review (e.g., theoretical and/or conceptual definitions).
• Validity comes from careful item construction and consideration of what each
item is meant to measure, then testing against model expectations.
The content validity index (CVI) is widely used for quantifying content validity
for scales. Item-level CVI (I-CVI) is calculated by having experts to rate the rele-
vance of each item to its own subdomain (1 = not relevant, 2 = somewhat relevant,
3 = quite relevant, 4 = highly relevant). The I-CVI of each item is defined as the
number of experts offering a rating of 3 or 4, divided by the total number of experts.
As an adjustment for chance agreements, the multi-rater kappa statistic (K*) was
adopted and is described as follows:
p
n
AnAn
c= -
()éëê
êùûú
ú́
!
!!05.where Pc is the probability of chance agreement, n is the number of experts, and A
is the number approving with good relevance. K* was calculated using the I-CVI
and the probability of chance agreement as follows:
K
P
P*= --ICVI c(^1) c
Each item on the scale was then rated as “fair,” “good,” or “excellent,” based on the
following rating criteria: fair, K = 0.40–0.59; good, K = 0.60–0.74; excellent,
K* > 0.74. Any item that received a “fair” rating was deleted [ 52 ].
Construct Validity
- Within-scale analyses
Extent to which a distinct construct is being measured and that items can be
combined to form a scale score.
• Cronbach alpha for scale scores >0.70
• Fit residuals (item-person interaction) within given range +/−2.5
• ITC > 0.30
• Homogeneity coefficient (IIC mean and range >0.3).
M. El Gaafary