The Intention of Inhaled Medication Adherence Scale (IMAS): The Development of a New Instrument for Assessing Inhaled Medication Adherence Among Patients with Chronic Obstructive Pulmonary Disease (COPD) Using Theory of Planned Behavior

Figures & data

Table 1 Patient Demographics (N=235)

		n (%)
Age (in years)		73.12 (16.7)^a
Sex	Male	220 (93.6%)
Smoking history	Non smoker	37 (15.7%)
	Active smoker	57 (24.3%)
	Ex-smoker	141 (60.0%)
Family support	Solitary	47 (20.0%)
	Caregiver	188 (80.0%)
Education	Uneducated	42 (17.9%)
	Elementary school	97 (41.3%)
	Junior high school	38 (16.2%)
	High school	52 (22.1%)
	College or above	6 (2.5%)
Number of comorbidities	No comorbidity	81 (34.5%)
	1 comorbidity	76 (32.3%)
	≥2 comorbidities	78 (33.2%)
Top 5 comorbidities	Hypertension	93 (39.5%)
	Heart disease	54 (30.0%)
	Diabetes	42 (17.9%)
	Chronic liver disease	21 (9.0%)
	Chronic kidney disease	16 (6.3%)
COPD Group	Low risk	218 (92.8%)
	High risk	17 (7.2%)
COPD GOLD	I (Mild)	83 (35.3%)
	II (Moderate)	95 (40.4%)
	III (Severe)	41 (17.6%)
	IV (Very severe)	16 (6.8%)
COPD Duration (Year)		4.40 (2.66)^a

Note: ^aReported in mean (SD).

Abbreviations: COPD, chronic obstructive pulmonary disease; GOLD, Global Initiative for Chronic Obstructive Lung Disease.

Table 2 Item Properties of the Intention of Inhaled Medication Adherence Scale (IMAS)

TPB Item	Mean (SD)	Skewness	Kurtosis	Initial Loading	Retained or Deleted	Retained Item Loading	CITCs
Attitude (AT; item score range 1–5)
AT1	4.29(0.68)	−0.45	−0.82	0.77	Retained	0.77	0.68
AT2	4.41(0.53)	−0.07	−1.12	0.68	Retained	0.67	0.60
AT3	4.06(0.68)	−0.08	−0.84	0.80	Retained	0.83	0.81
AT4	4.00(0.72)	−0.07	−0.88	0.77	Retained	0.80	0.78
AT5	3.74(0.77)	0.49	−1.14	0.71	Retained	0.75	0.72
AT6	3.87(0.75)	0.21	−1.20	0.78	Retained	0.80	0.79
AT7	3.86(0.72)	0.21	−1.03	0.82	Retained	0.85	0.84
AT8	3.74(0.73)	0.37	−0.93	0.74	Retained	0.77	0.78
AT9	4.40(0.97)	−1.61	1.57	0.21	Deleted	–	–
AT10	4.36(1.00)	−1.59	1.48	0.18	Deleted	–	–
AT11	4.51(0.87)	−2.02	3.62	0.31	Deleted	–	–
AT12	4.49(0.95)	−1.81	2.13	0.36	Deleted	–	–
AT13	4.09(0.75)	−0.53	0.03	0.69	Retained	0.67	0.62
Subjective Norms (SN; item score range 1–5)
SN1	3.48(0.75)	1.18	−0.18	0.16	Deleted	–	–
SN2	3.38(0.66)	1.51	0.91	0.08	Deleted	–	–
SN3	4.55(0.59)	−1.03	0.77	0.87	Retained	0.83	0.68
SN4	4.45(0.61)	−0.85	0.93	0.87	Retained	0.83	0.68
Perceived Behavioral Control (PBC; item score range 1–5)
PBC1	4.78(0.48)	−2.58	8.75	0.78	Retained	0.86	0.82
PBC2	4.74(0.56)	−2.66	8.55	0.67	Retained	0.77	0.87
PBC3	4.78(0.45)	−2.20	6.14	0.85	Retained	0.94	0.89
PBC4	4.77(0.50)	−2.52	8.07	0.76	Retained	0.85	0.89
PBC5	4.77(0.48)	−2.17	5.49	0.84	Retained	0.93	0.86
PBC6	4.72(0.54)	−1.82	2.38	0.97	Deleted	–	–
Intention (IT; item score range 1–5)
IT1	4.72(0.57)	−2.37	6.46	0.20	Deleted	–	–
IT2	4.75(0.53)	−2.39	6.57	0.28	Deleted	–	–
IT3	3.75(1.20)	−0.37	−1.31	0.79	Retained	0.80	0.64
IT4	3.80(1.20)	−0.50	−1.19	0.88	Retained	0.92	0.88
IT5	3.82(1.16)	−0.45	−1.28	0.84	Retained	0.87	0.86

Abbreviation: CITCs, corrected item-total correlations.

Table 3 Goodness-of-Fit Indices for Confirmatory Factor Analysis

Fit Indices (Initial)
χ^2	df	p-value	χ^2/df	CFI	TLI	RMSEA	SRMR
739.51	344	<0.001	2.15	0.95	0.94	0.07	0.12
Fit Indices (Final)
χ^2	df	p-value	χ^2/df	CFI	TLI	RMSEA	SRMR
122	146	0.93	0.83	1.00	1.00	0.00	0.06

Note: estimator: diagonally weighted least squares.

Abbreviations: df, degrees of freedom; CFI, comparative fit index; TLI, Tucker Lewis index; RMSEA, root-mean-square error of approximation; SRMR, standardized root mean square residual.

Table 4 Cronbach’s α, Composite Reliability (CR), and Average Variance Extracted (AVE) in the Intention of Inhaled Medication Adherence Scale (IMAS) Constructs

Constructs	Number of Items	α	CR	AVE
Attitude (AT)	9	0.93	0.93	0.59
Subjective Norm (SN)	2	0.81	0.81	0.68
Perceived Behavioral Control (PBC)	5	0.95	0.94	0.77
Intention (IT)	3	0.89	0.90	0.75

Notes: α > 0.7 indicates good internal consistency; CR > 0.6 and AVE > 0.5 indicate good convergent validity.

Table 5 Divergent Validity of the Intention of Inhaled Medication Adherence Scale (IMAS) Using Fornell-Larcker Criterion Matrix

Constructs	AT	SN	PBC	IT
Attitude (AT)	0.77
Subjective Norm (SN)	0.45	0.83
Perceived Behavioral Control (PBC)	0.25	0.38	0.87
Intention (IT)	0.38	0.40	0.21	0.86

Notes: The diagonal values are square root of the average variance extracted (AVE); the lower triangular values are correlations between constructs. When square root of the AVE (diagonal values) of a construct larger than the correlations between the construct and other constructs, the divergent validity is supported.