Review: propensity score methods with application to the HELP clinic clinical study

Figures & data

Figure 1 Flowchart of subjects’ selection with addiction in the HELP clinic clinical study.

Note: *MMS score, max 30.
Abbreviations: HELP, Health Evaluation and Linkage to Primary care; MMS, Mini-Mental State.

Table 1 Association of Homeless with demographics characteristics and baseline measures for the HELP clinic clinical data

Variables	Total (N = 468)	Homeless (N = 217)	Housed (N = 251)	P-value
Sex				0.039
Female	111 (23.7)	42 (19.4)	69 (27.5)
Male	357 (76.3)	175 (80.6)	182 (72.5)
Race				0.027
Black	216 (46.2)	86 (39.6)	130 (51.8)
Hispanic	51 (10.9)	22 (10.1)	29 (11.6)
White	173 (37.0)	95 (43.8)	78 (31.1)
Other	28 (6.0)	14 (6.5)	14 (5.6)
Substance				<0.001^a
Alcohol	185 (39.5)	109 (50.2)	76 (30.3)
Cocaine	155 (33.1)	59 (27.2)	96 (38.2)
Heroin	127 (27.1)	48 (22.1)	79 (31.5)
Missing	1 (0.2)	1 (0.5)	0 (0.0)
SAT				0.056
No	337 (72.0)	147 (67.7)	190 (75.7)
Yes	131 (28.0)	70 (32.3)	61 (24.3)
Suicide				0.003
No	335 (71.6)	141 (65.0)	194 (77.3)
Yes	133 (28.4)	76 (35.0)	57 (22.7)
Randomization				0.308
No	234 (50.0)	114 (52.5)	120 (47.8)
Yes	234 (50.0)	103 (47.5)	131 (52.2)
US				0.757
No	58 (12.4)	29 (13.4)	29 (11.6)
Yes	195 (41.7)	93 (42.9)	102 (40.6)
Missing	215 (45.9)	95 (43.8)	120 (47.8)
LP				0.446
No	280 (59.8)	127 (58.5)	153 (61.0)
Yes	165 (35.3)	81 (37.3)	84 (33.5)
Missing	23 (4.9)	9 (4.1)	14 (5.6)
Age				0.068
Frequency	468	217	251
Mean (95% CI)	35.74 (35.03–36.44)	36.44 (35.34–37.55)	35.12 (34.22–36.03)
Median (min – max)	35 (18–60)	36 (18–60)	34 (21–58)
AD				<0.001
Frequency	468	217	251
Mean (95% Cl)	18.28 (16.46–20.11)	23.48 (20.36–26.60)	13.79 (11.87–15.71)
Median (min – max)	13 (0–142)	19 (0–142)	10 (0–76)
MD				<0.001
Frequency	468	217	251
Mean (95% CI)	25.06 (22.48–27.64)	31.27 (26.92–35.62)	19.68 (16.84–22.53)
Median (min – max)	18.5 (0–184)	25 (0–179)	13 (0–184)
Hospitalizations				0.132
Frequency	468	217	251
Mean (95% CI)	3.09 (2.53–3.66)	3.56 (2.84–4.28)	2.69 (1.84–3.54)
Median (min – max)	2 (0–100)	2 (0–40)	1 (0–100)
TS				0.732
Frequency	251	122	129
Mean (95% CI)	75.4 (68.2–82.6)	73.6 (63.1–84.2)	77.1 (67.2–87.0)
Median (min – max)	33.0 (0.0–268.0)	32.0 (0.0–252.0)	35.0 (0.0–268.0)
Missing	217	95	122
TLP				0.849
Frequency	445	208	237
Mean (95% CI)	257.6 (243.9–271.2)	256.1 (236.1–276.1)	258.8 (240.2–277.5)
Median (min – max)	364.0 (2.0–456.0)	358.0 (2.0–449.0)	365.0 (4.0–456.0)
Missing	23	9	14
Times				0.032
Frequency	220	140	80
Mean (95% CI)	2.5 (2.3–2.7)	2.8 (2.4—3.1)	2.0 (I.8–2.2)
Median (min – max)	2.0 (1.0–21.0)	2.0 (1.0–21.0)	1.0 (1.0–11.0)
Missing	248	77	171
CESD				0.048
Frequency	468	217	251
Mean (95% CI)	32.87 (31.74–34.00)	34.10 (32.46–35.73)	31.81 (30.26–33.37)
Median (min – max)	34 (1–60)	36 (1–60)	32 (3–58)
RABDR				0.380
Frequency	466	216	250
Mean (95% CI)	1.9 (I.5–2.3)	2.1 (1.4—2.7)	1.7 (I.2–2.2)
Median (min – max)	0.0 (0.0–21.0)	0.0 (0.0–21.0)	0.0 (0.0–21.0)
Missing	2	1	1
IDUC				<0.001
Frequency	454	210	244
Mean (95% CI)	35.7 (35.1–36.4)	37.4 (36.5–38.2)	34.3 (33.4–35.2)
Median (min – max)	37.5 (4.0–45.0)	39.5 (9.0–45.0)	36.0 (4.0–45.0)
Missing	14	7	7
RABSR				0.037
Frequency	467	216	251
Mean (95% CI)	4.6 (4.4–4.9)	4.9 (4.5–5.3)	4.4 (4.I–4.7)
Median (min – max)	4.0 (0.0–14.0)	5.0 (0.0–14.0)	4.0 (0.0–14.0)
Missing	1	1	0
Support				<0.001
Frequency	468	217	251
Mean (95% Il)	6.67 (6.31–7.04)	5.99 (5.48–6.50)	7.26 (6.76–7.764)
Median (min – max)	7 (0–14)	5 (0–14)	7(0–14)
MCS				0.138
Frequency	468	217	251
Mean (95% CI)	31.5 (30.4–32.7)	30.6 (29.0–32.2)	32.4 (30.7–34.0)
Median (min – max)	28.6 (6.8–62.2)	27.8 (9.2–60.5)	30.7 (6.8–62.2)
PCS				0.054
Frequency	468	217	251
Mean (95% Cl)	48.1 (47.1–49.0)	47.0 (45.6–48.5)	49.0 (47.6–50.3)
Median (min – max)	48.9 (14.1–74.8)	47.0 (21.9–71.6)	51.0 (14.1–74.8)

Note: ^aFisher’s exact test.

Abbreviations: HELP, Health Evaluation and Linkage to Primary care; SAT, any substance abuse treatment; Suicide, serious thoughts of suicide in last 30 days; US, use of any substance post-detox; LP, post-detox linkage to primary care; AD, average number of drinks consumed per day in the past 30 days; MD, maximum number of drinks consumed per day in the past 30 days; TS, time to first use of any substance post-detox; TLP, time (in days) to linkage to primary care; CESD, center for epidemiologic studies depression measure; RABDR, risk assessment battery drug risk scale; IDUC, inventory of drug use consequences total score; RABSR, risk assessment battery sex risk score; MCS, mental quality of life component score; PCS, physical quality of life component score.

Table 2 Effects of Homeless on PCS using the propensity score adjusted for covariates

Method	Estimate	Standard error	95% CI	P-value
Two group comparison	−1.9	1.0	(−3.87, 0.03)	0.054
Standard covariate adjustment	−1.1	1.0	(−3.04, 0.92)	0.295
Matching	−1.3	1.1	(−3.52, 0.84)	0.227
Stratification	−1.4	1.1	(−3.52, 0.69)	0.188
Inverse probability of treatment weight	−2.06	1.0	(−4.06, −0.07)	0.042
Covariate adjustment	−1.2	1.1	(−3.26, 0.97)	0.288

Abbreviation: PCS, physical quality of life component score.

short-legendBox 1

short-legendBox 2

Figure 2 Side-by-side boxplot for the significant continuous covariates (CESD, AD, Support, IDUC, RABSR), which are included in Table 1.

Notes: Here yellow colors and brown colors denote the treated (homeless) and untreated (housed) subjects, respectively, the slope of the black lines denotes the expected differences in covariates between the two groups, and the numbers are the sample sizes of the subjects in each of the two groups.
Abbreviations: CESD, center for epidemiologic studies depression measure; AD, average number of drinks consumed per day in the past 30 days; Support, perceived social support by friends; IDUC, inventory of drug use consequences total score; RABSR, risk assessment battery sex risk score.

short-legendBox 3

Figure 3 Side-by-side barplots for the significant categorical covariates (sex, Suicide, race, Substance), which are included in Table 1.

Note: Here the same colors represent the same level of the variables; A and B represent treated (homeless) and untreated (housed), respectively.
Abbreviations: Suicide, serious thoughts of suicide in last 30 days; Substance, primary substance of abuse.

short-legendBox 4