Table 2.

Parameters in Computer Simulation^*

Parameter	Data Source (Reference)	Strength of Evidence			Does Data Source Meet Strict Evidence Criteria?				Parameter Distribution if Data Source Used	Parameter Distribution if Data Source Not Used
		Study Design	Internal Validity	External Validity	Study Design Level 1	Internal Validity Good	External Validity High	All 3 Criteria
Mortality rate in absence of HIV	Observational; life tables (12)	1	Good	Low	Yes	Yes	No	No	Point estimates, variable	Uniform (0.5X, 1.5X estimates)
Mortality rate attributable to HIV	Observational; 1 study in similar population (13)	1	Good	Low	Yes	Yes	No	No	Normal (0.19, 0.06)	Uniform (0, 0.38)
Impact of HIV treatment on mortality	Observational; 13 studies pooled from similar populations (14)	1	Good	High	Yes	Yes	Yes	Yes	Normal (0.15, 0.02)	NA
Probability of taking HIV medications	Observational (15)	1	Fair	Low	Yes	No	No	No	Never used†	NA
	Observational (16)	1	Good	High	Yes	Yes	Yes	Yes	Normal (0.75, 0.02)	NA
	Observational (17)	1	Good	Low	Yes	Yes	No	No	Never used†	NA
	Observational (18)	1	Good	Low	Yes	Yes	No	No	Never used†	NA
Effectiveness of DOT	Randomized, controlled trial; 1 study in dissimilar population (19)	1	Good	Low	Yes	Yes	No	No	Normal (0.46, 0.01)	Uniform (0, 2)
Utility with HIV	Observational; 1 study in similar population (20)	1	Poor	Low	Yes	No	No	No	Normal (0.87, 0.04)	Uniform (0.5, 1.0)
Decrement in utility with HIV treatment	Observational; 1 study in similar population (unpublished)	1	Poor	Low	Yes	No	No	No	Normal (0.05, 0.01)	Uniform (0, 0.5)
Annual cost of DOT	Expert opinion	3	Poor	Low	No	No	No	No	Never used†	NA
	Observational; 1 study in dissimilar population (21)	2-2	Good	Low	No	Yes	No	No	Point estimate $4600	Uniform ($200, $36 500)
	Observational; 1 study in dissimilar population (22)	2-2	Poor	Low	No	No	No	No	Never used†	NA
	Observational; 1 study in dissimilar population (23)	2-2	Poor	Low	No	No	No	No	Never used†	NA
Annual cost of nondrug HIV care	Observational; 1 study in similar population (24)	1	Poor	High	Yes	No	Yes	No	Normal ($9000, $300)	Uniform ($200, $20 000)
	Observational; 1 study in similar population (25)	1	Poor	High	Yes	No	Yes	No	Never used†	NA
Annual cost of HIV drugs	Observational; 1 study in similar population (25)	1	Good	High	Yes	Yes	Yes	Yes	Normal ($10 300, $700)	NA

^*Individual data sources were eligible to inform parameter estimations if their strength of evidence met or exceeded criteria in 3 separate domains (study design, internal validity, and external validity). If no data sources met strength of evidence criteria, a uniform distribution across a wide plausible range was substituted. When more than 1 study met strength of evidence criteria, the parameter’s distribution was based on the study with the most precise statistical estimate. Normal = normal distribution (mean, standard deviation); uniform = uniform distribution (lower bound, higher bound). DOT = directly observed therapy; NA = not applicable because data source either was never used or met all 3 of the strict evidence criteria.

^† “Never used” because results were statistically less precise than those of another study or studies with equal or superior grades of evidence in all 3 domains. It is also possible that a particular data source could be statistically more precise but have lower strength of evidence than alternative data sources, although this situation did not arise with our example. In accord with our decision rules, we would have used the statistically more precise data source when evidence criteria were more inclusive and the statistically less precise data source when evidence criteria were less inclusive.