Results: Factor and Convergent Validity Analyses

As noted in Table 4.6, five factors were confirmed providing support for Rogers’s Model. All 28 items had factor loadings > 0.40: range = 0.43 to 0.81. There was also a significant association (p = 0.01) between the DCC SAS score and DCC SCRIPTPII.

In addition to identifying a five-factor model, analyses of the relationship of all five factors provided additional evidence supporting the convergent validity of “Rogers’s Diffusion of Innovation Theory.” Data in Table 4.7 confirmed consistent and statistically significant (p > 0.01) relationships between the five-attribute SAS sub-scales.

SAS Internal Consistency and Stability

The SAS internal consistency r was 0.93 and stability r was 0.76. All 28 item-to-total correlation coefficients were r > 0.30. As noted in Table 4.8, the final SAS scale consists of 28 items that had good validity, excellent overall reliability (alpha = 0.93), and borderline (0.67) to very good (0.88) sub-scale reliability. The sub-scale test-retest reliability was consistently below or at the cutoff for reliability: 0.60 to 0.73. The stability coefficient was adequate: 0.76. Although two of five subscales need to be improved by increasing stability, the SAS can be adapted by prenatal care programs to measure the attributes of adoption of new patient education methods.

Another excellent measurement study concerning how to establish the psychometric properties of a scale to measure adherence was conducted by Morisky et al., “Predictive Validity of a Medication Adherence Measure (MAS) in an Outpatient Setting,” Journal of Clinical Hypertension (2008), 348-354. Analyses of an eight-item MAS from 1,367 low-income patients confirmed all factor loadings were > 0.40, the alpha r was 0.83, and all

table 4.6 Factor Loading and T-values of the Five-Factor 28-item SAS Scale

factor items

factor loading

t-value

Relative Advantage

9 Items

Q1

0.68

6.97

Q2

0.72

7.40

Q3

0.66

6.71

Q7

0.71

7.32

Q9

0.58

5.69

Q11

0.48

4.49

Q14

0.80

8.72

Q23

0.72

7.42

Q36

0.73

7.64

Compatibility

4 Items

Q5

0.67

6.75

Q8

0.80

8.50

Q15

0.76

8.00

Q19

0.72

7.40

Complexity

7 Items

RQ22

0.81

8.80

Q24

0.63

6.24

RQ25

0.48

4.51

RQ26

0.64

6.34

Q29

0.77

8.16

RQ34

0.70

7.16

Q42

0.71

7.16

Observability

4 Items

Q33

0.43

4.06

RQ38

0.61

5.91

Q39

0.72

7.32

RQ41

0.56

5.34

Trialability

4 Items

Q27

0.52

4.85

RQ30

0.62

5.95

RQ32

0.49

4.58

RQ37

0.47

4.33

table 4.7 SAS Sub-Scale Convergent Validity Correlational Analyses

sub-scale

advantage

compatibility

complexity

observabi lity

Compatibility

0.93

Complexity

0.60

0.66

Observability

0.81

0.65

0.93

Trialability

0.51

0.62

0.97

0.94

scale factors: sub-scales

cronbach

alpha

test-retest reliabi lity*

Relative Advantage: 9 Items

0.88

0.74 (p < 0.0001)

Compatibility: 4 Items

0.82

0.62 (p < 0.0001)

Complexity: 6 Items

0.83

0.73 (p < 0.0001)

Observability: 4 Items

0.67

0.60 (p < 0.0001)

Trialability: 5 Items

0.71

0.67 (p < 0.0001)

Total Score: 28 Items

0.93

0.76 (p < 0.0001)

* Pearson Correlation

eight items had item-to-total correlations of > 0.30. The MAS predicted BP control.

 
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