The influence of co-morbidities on prescribing pharmacotherapy for insomnia: evidence from US national outpatient data 1995–2004

Figures & data

Table 1.  Descriptive statistics of the study population (unweighted population size = 5,487 cross-sectional patient visits from 1995 to 2004).

Variable	Measure	Proportion (%)
Patient demographics
Age groups (years)	18–34*^†	12.06
	35–49^†	29.29
	50–64^†	27.94
	≥65*^†	30.71
Gender*	Male	39.58
Race^†	Hispanic	7.13
	White	90.14
Established (vs. new) patients		88.34
Source of payment	Private insurance*^†	44.41
	Public insurance*^†	38.53
	Other	17.06
Co-morbidities	Presence of mental co-morbidity*^†	41.21
	Charlson co-morbidity index*	Mean = 0.22 (sd 0.68)
List of five most prevalent	Episodic mood disorders*^†	14.94
co-morbidities	Anxiety*	15.60
	Essential hypertension	10.15
	Depressive disorder*^†	7.02
	Diabetes	3.50
Physician/practice characteristics	Physician owner of solo practice (only 2001–2004)*	38.49
Region	Northeast	21.72
	Midwest*	20.41
	South	33.97
	West^†	23.89
Practice in metropolitan area	Yes*^†	83.96
Physician specialty	Family practice and internal medicine	32.73
	Psychiatry*^†	29.80
	Neurology*	9.02
	Other*^†	28.45
Pharmacotherapy	Prescribed medication therapy at visit	32.55
	Benzodiazepine prescription rate among those receiving insomnia medications	34.32

sd, standard deviation.

* Significantly correlated with medication therapy prescription at p ≤0.05 significance level using χ2 tests.

^† Significantly correlated with benzodiazepine medication prescription at p ≤0.05 significance level using χ2 tests.

Figure 1.  Prevalence of co-morbidities in patients with insomnia (1995–2004).

Table 2.  Predictors of type of therapy prescribed for sleep difficulty during outpatient visit (weighted sample size = 107.4 million) by logistic regression^‡.

Independent variable	Dependent variable
	Medication therapy prescribed (OR (95% CI))	Medication therapy prescribed accounting for type of co-morbidity (OR (95% CI))
Charlson co-morbidity index	1.02 (0.91–1.14)	–
Presence of mental co-morbidity	0.64 (0.50–0.83)*	–
Number of co-morbidities	1.09 (0.98–1.22)	–
Anxiety	–	0.55 (0.43–0.70)*
Episodic mood disorders	–	0.89 (0.68–1.16)
Essential hypertension	–	0.84 (0.64–1.09)
Depressive disorder	–	0.99 (0.70–1.39)
Diabetes	–	0.99 (0.67–1.47)
Age (years)^†
35–49	1.39 (1.04–1.85)*	1.40 (1.05–1.87)*
50–64	1.44 (1.08–1.92)*	1.49 (1.12–1.99)*
≥65	1.27 (0.93–1.74)	1.37 (1.01–1.87)*
Male gender	0.99 (0.84–1.17)	0.99 (0.83–1.17)
White race	1.15 (0.87–1.52)	1.13 (0.86–1.49)
Established patient	1.38 (1.02–1.88)*	1.42 (1.05–1.92)*
Insomnia as primary diagnosis	0.44 (0.30–0.63)*	0.40 (0.29–0.55)*
Metropolitan area	1.27 (1.02–1.58)*	1.26 (1.01–1.57)*
Region^†
Northeast	0.82 (0.64–1.05)	0.82 (0.64–1.05)
Midwest	0.63 (0.49–0.80)*	0.62 (0.48–0.79)*
South	0.84 (0.68–1.04)	0.82 (0.67–1.02)
Source of payment^†
Public insurance	1.16 (0.94–1.44)	1.18 (0.95–1.46)
Other	0.95 (0.75–1.20)	0.94 (0.74–1.19)
Specialty^†
Psychiatry	1.70 (1.32–2.20)*	1.40 (1.11–1.77)*
Neurology	0.73 (0.54–0.99)*	0.68 (0.51–0.93)*
Other	0.81 (0.66–1.00)*	0.82 (0.66–1.00)*

OR, odds ratio; CI, confidence interval; NAMCS, National Ambulatory Medical Care Survey.* Significant at p <0.05.^† For individual categorical independent variables with more than two categories, the dropped reference categories are age group 18–34 years, East region, private insurance, and family practice and internal medicine specialty.^‡ All analyses were weighted using the NAMCS sampling weights. Variables significant in univariate analyses are included in the multivariate models.

Table 3.  Physician and patient predictors of non-benzodiazepine prescription for sleep difficulty at outpatient visits (weighted sample size = 54.0 million) by logistic regression^‡.

Independent variable	Dependent variable
	Non-benzodiazepine prescription (OR (95% CI))	Non-benzodiazepine prescription accounting for type of co-morbidity (OR (95% CI))
Charlson co-morbidity index	1.06 (0.87–1.29)	–
Number of co-morbidities	1.14 (0.95–1.36)	–
Presence of mental co-morbidity	1.21 (0.75–1.95)	–
Anxiety	–	0.97 (0.61–1.54)
Episodic mood disorders	–	1.95 (1.27–3.01)*
Essential hypertension	–	1.56 (0.98–2.49)
Depressive disorder	–	1.73 (0.91–3.31)
Diabetes	–	1.01 (0.49–2.09)
Age (years)^†
35–49	0.55 (0.30–1.00)*	0.52 (0.28–0.94)*
50–64	0.61 (0.34–1.11)	0.58 (0.32–1.06)
≥65	0.43 (0.23–0.79)*	0.41 (0.22–0.75)*
Hispanic race	0.57 (0.33–1.00)*	0.57 (0.32–1.01)
Insomnia as primary diagnosis	2.73 (1.27–5.85)*	2.51 (1.18–5.32)*
Source of payment^†
Public insurance	0.58 (0.39–0.86)*	0.59 (0.40–0.88)*
Other	0.57 (0.38–0.86)*	0.58 (0.38–0.87)*
Practice in metropolitan area	1.50 (1.01–2.22)*	1.44 (0.97–2.12)
Region^†
Northeast	1.63 (1.05–2.53)*	1.60 (1.03–2.50)*
Midwest	1.15 (0.73–1.80)	1.16 (0.74–1.82)
South	1.14 (0.78–1.66)	1.14 (0.78–1.67)
Specialty^†
Psychiatry	0.81 (0.49–1.36)	0.68 (0.45–1.03)
Neurology	1.05 (0.59–1.87)	1.06 (0.59–1.90)
Other	0.72 (0.50–1.03)	0.75 (0.52–1.08)

OR, odds ratios; CI, confidence interval; NAMCS, National Ambulatory Medical Care Survey.

*Significant at p <0.05.

^†For individual categorical independent variables with more than two categories, the dropped reference categories are age group 18–34 years, private insurance, East region and internal medicine physician.

^‡All analyses were weighted using the NAMCS sampling weights.