Reliability and validity of a single-item rating scale to monitor medication adherence for people living with HIV and lower health literacy

Figures & data

Table 1. Means and standard deviations of computerized and phone administered single-item rating scale (SIRS) and unannounced pill count adherence

	Total sample		Lower literacy		Moderate literacy
	n = 468		n = 267		n = 201
	M	SD	M	SD	M	SD
Phone – administered SIRS
Time 1	91.9	14.7	92.5	14.7	91.1	14.7
Time 2	90.2	18.1	91.1	16.7	88.8	20.0
Time 3	89.7	19.1	90.2	19.5	89.0	18.8
Time 1–3 mean	90.2	15.1	90.8	14.6	89.3	15.7
Unannounced pill count
Time 1	85.3	19.7	86.3	18.6	83.9	21.1
Time 2	83.9	22.3	84.4	21.7	83.0	23.0
Time 3	84.2	22.5	85.0	23.1	83.0	21.7
Time 1–3 mean	84.1	17.8	85.0	16.8	82.6	19.2
Computerized SIRS	87.0	19.3	88.7	17.5	84.9	21.4
Paired t-tests	t (df)		t (df)		t (df)
Mean phone SIRS – mean unannounced pill counts	9.31** (438)		6.1** (250)		7.7** (184)
Mean unannounced pill counts – computerized SIRS	− 3.1** (436)		− 3.1** (248)		− 1.2 (184)
Mean phone SIRS – computerized SIRS	4.0** (448)		1.9** (253)		3.7** (191)

Note:

** P < 0.01.

Table 2. Test–retest reliability coefficients for phone administered SIRS and unannounced pill count adherence

	Total sample	Lower literacy	Moderate literacy	z-score comparing correlations by literacy
	n = 468	n = 267	n = 201
	r	r	r
Phone – delivered SIRS
Time 1 – Time 2	0.522**	0.418**	0.627**	− 3.097**
Time 2 – Time 3	0.468**	0.409**	0.542**	− 1.836
Unannounced pill count (unannounced pill counts)
Time 1 – Time 2	0.495**	0.436**	0.564**	− 1.823
Time 2 – Time 3	0.439**	0.454**	0.419**	− 0.907

Note: UPC = unannounced pill count, SIRS = single-item rating scale.

* P < 0.05,

** P < 0.01.

Table 3. Correlation matrix of adherence measures by literacy subgroups

		Moderate literacy
		Phone SIRS 1	Phone SIRS 2	Phone SIRS 3	UPC 1	UPC 2	UPC 3	Computer SIRS
Lower literacy	Phone SIRS 1	1	0.627**	0.540**	0.606**	0.539**	0.469**	− 0.297**
	Phone SIRS 2	0.418**	1	0.542**	0.613**	0.686**	0.544**	− 0.403**
	Phone SIRS 3	0.471**	0.409**	1	0.370**	0.452**	0.679**	− 0.217**
	UPC 1	0.306**	0.295**	0.283**	1	0.564**	0.402**	− 0.308**
	UPC 2	0.250**	0.614**	0.317**	0.426**	1	0.419**	− 0.301**
	UPC 3	0.316**	0.280**	0.712**	0.403**	0.454**	1	− 0.236**
	Computer SIRS	− 0.209**	− 0.203**	− 0.297**	− 0.235**	− 0.366**	− 0.358**	1

Note: UPC =  = single-item rating scale.

** P < 0.01.

Table 4. Concurrent validity (Panel 1), modality effects (Panel 2), and predictive validity (Panel 3)

		Total sample		Lower literacy		Moderate literacy		Comparisons by literacy group
		n = 468		n = 267		n = 201
Panel 1		r		r		r		z-score comparing r's
	Continuous phone SIRS & UPC
	Time 1	0.438**		0.306**		0.606**		− 4.11**
	Time 2	0.648**		0.614**		0.686**		− 1.33
	Time 3	0.700**		0.712**		0.679**		0.68
	Mean UPC and SIRS	0.660**		0.534**		0.796**		− 5.23**
	Categorical UPC and phone SIRS	X^2	K	X^2	K	X^2	K	z-score comparing kappas
	Time 1	72.391**	0.215**	29.142**	0.179**	56.285**	0.270**	− 1.020
	Time 2	107.799**	0.293**	43.574**	0.238**	77.683**	0.353**	− 1.343
	Time 3	112.103**	0.250**	57.163**	0.227**	57.695**	0.281**	− 0.614
Panel 2		r		r		r		z-score comparing r's
	Phone SIRS & computer SIRS	0.428**		0.399**		0.454**		− 0.720
		X^2	K	X^2	K	X^2	K	z-score comparing kappas
	Categorical phone SIRS & computer SIRS	121.190**	0.309**	73.055**	0.275**	66.983**	0.342**	− 0.788
Panel 3		r		r		r		z-score comparing r's
	UPC & computer SIRS	0.404**		0.353**		0.454**		− 1.29
		X^2	K	X^2	K	X^2	K	z-score comparing kappas
	Categorical UPC & computer SIRS	53.523**	0.220**	37.231**	0.218**	20.792**	0.223**	− 0.056

Note: UPC = unannounced pill count, SIRS = single-item rating scale.

** P < 0.01.

Table 5. Criterion-related validity coefficients for medication adherence measures and HIV RNA viral load

	Total sample	Lower literacy	Moderate literacy	z-score comparing correlations by literacy
	n = 468	n = 267	n = 201
	r	r	r
Phone SIRS – viral load	− 0.250**	− 0.209**	− 0.297**	1.00
Computer SIRS – viral load	− 0.366**	− 0.291**	− 0.444**	1.89
Unannounced pill counts viral load	− 0.269**	− 0.235**	− 0.308**	0.84

Note: UPC = unannounced pill count, SIRS = single-item rating scale.

** P < 0.01.

Table 6. Bivariate linear regressions on absolute value of discrepancy between phone SIRS and unannounced pill counts

				Multivariate model
Variables	B	SE B	β	B	SE B	β
Gender	− 0.812	1.169	− 0.033
Ethnicity	0.503	1.339	0.018
Education	− 0.001	0.283	0.001
Income	− 1.778	0.83	− 0.102	− 1.87	0.825	− 0.107
Employment	− 0.374	0.539	− 0.033
Reading literacy	− 3.152	2.523	− 0.060
Numerical literacy	− 0.392	0.290	− 0.064
Clock test	0.427	0.416	0.49
Years since testing positive	− 0.098	0.077	− 0.065
Shame	0.056	0.107	0.025
Social support	− 0.155	0.072	− 0.102	− 0.132	0.072	− 0.087
Stress	0.141	0.140	0.050
Depression	0.074	0.098	0.036
Alcohol	0.616	0.0234	0.125**	0.627	0.234	0.127**
Substance use	1.101	0.680	0.077

Note:

* P < 0.05,

** P < 0.01.