*! version 1.2.2 19Mar2020 by Mead Over, Center for Global Development

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AIDS Difference Analysis

aidsdif
avarlist
,
bl(bl_filename)
s1(s1_filename)
[
options
]

Description

aidsdif calculates estimates of the impact of alternative AIDS
treatment scenarios relative to a user-designated baseline projection.
The program is a companion to, and requires the output from,
the program aidsproj. The program aidsproj projects
various outcomes, including the fiscal burden and AIDS deaths, for
individual or aggregates of countries as a result of a specified set of
assumptions about AIDS treatment policy, its cost and effects.
aidsdif analyzes the output from two or more runs of aidsproj
in order to estimate the impact of alternative specifications.
When a variation in aidsproj assumptions can be interpreted as a
difference in policy, aidsdif's output can be interpreted as
estimating the cost-effectivness of that policy.

aidsdif uses data files produced by aidsproj in order to
compute the difference in projected future outcomes which would occur as
a result of any assumptions that differ between the aidsproj
projection runs. aidsdif requires that one data file be designated
the "Baseline" projection and a second be designated the "Scenario 1"
projection. Additional files can be designated as "Scenario 2" "Scenario
3" etc. up to a maximum of six such scenarios. A difference computed by
aidsdif between Scenario X and the Baseline projection can be
thought of as an impact of Scenario X relative to the Baseline.

A standard run computes for all countries the difference between each of
the "scenarios" and the "baseline" for each of the analyzed variables in
avarlist. One of these variables is identified as the "cost
variable" and another as the "effect" or "benefit" variable. Using these
two variables, the program computes the ratio of costs to effects for
each country in each year as well as the estimated cost-effectiveness of
each scenario relative to the baseline. The program prints a table of
the weighted-average cost-effectiveness for all countries in each region
and world-wide, where the countries are weighted by the number of people
on anti-retroviral therapy. Optional output includes charts of the
several versions of each of the analysis variables and of the impacts on
those variables of each scenario relative to the baseline.

aidsdif calls program rescale which must be on the
adopath.

Analysis Variables

The program requires the user to specify as avarlist a list of at
least two variables, which are found in the Baseline and all the
Scenario projection runs. Typically these variables will include a
measure of the total cost of each run (e.g. costtot) and a
measure of the effect of the run (e.g. d). The program then generates
a new data file which contains a version of each avarlist variable
from each scenario. The variables are distinguished by prefixes
bl_V for the Baseline run and s1_V through s6_V for the
Scenario runs, where V is the original avarlist variable. The
program then computes the difference between the Scenario version of a
variable and the Baseline version and retains the results as
difX_V, where X is the Scenario number.

Required options

The program has only two required "options",
bl(bl_filename) and s1(s1_filename) ,
which specify respectively the baseline and the Scenario 1 data files.

Analysis options

drate(####) Specifies the discount rate used for
computing the present values of costs and benefits and thus the
cost-effectiveness ratio. Default is 0.03.

refyear(####) Reference year to which costs and
benefits are discounted and for which the cost-effectiveness ratio is
computed. Default is 2008.

costvar(cvarname) Variable to be treated as the
"cost variable" in computations of cost-effectiveness. The present value
of the future stream of this variable serves as the numerator of the
cost-effectivness ratio. cvarname must be a "flow" variable.
Default is the variable costtot.

costunit(cunit) String giving the unit in which
costvar is measured. Default is "Thousands of dollars".

benvar(bvarname) Variable to be treated as the
"effect variable" or "benefit variable" in computations of
cost-effectiveness. The present value of the future stream of this
variable serves as the denominator of the cost-effectivness (or cost-benefit) ratio.
bvarname must be a "flow" variable. The default is the variable life-years
ly, which is the additional number of people alive in a scenario in each
year compared to the baseline.
Other options include deaths (d), death-years (dy) or the value of
statistical life years (vlsy).
The value of a life-year gained is
assumed to be equal to projected per capita GDP.
The cost-effectiveness ratio is defined as the
absolute value of the ratio of changes in costvar to changes in
benvar.

benunit(bunit) String giving the unit in which
benvar is measured. By default the benunit is determined by
the choice of benvar. For example, with the default benvar of ly,
the default benunit is life-years. With the benvar of vlsy,
the default benunit is thousands of US dollars.

othvar(ovarlist) A list of additional variables
from the Baseline data set which are to be retained in the aidsdif
data set. These variables are not differenced across scenarios. They can
be used as reference variables for further analysis of the differenced
data set. Typically they would be variables such as a country's national
income which do not vary across simulation runs.

Basic Output options (Output 1 tab)

If no output options are specified, the program uses default
values of the optional parameters, computes and displays the impact of
each scenario relative to the baseline on each of the avarlist
variables and halts.

If the user specifies the option countries(clist),
then for each country in clist the program presents the projection
results in tabular form. If the user specifies the option world or
regions(rlist), the program computes the weighted averages
for the specified aggregate(s). Quantity or cost/expenditure projections
are summed across the specified group of countries while percentages or
rates are averaged. Averages are weighted by the number of people
receiving antiretroviral treatment in the given year in the respective
countries (not by their number of HIV infected, total populations or
GDP).

countries(clist) Use World Bank's
3-letter country names to specify countries for which results are
tabulated and, if graph options specified, displayed. Specified
countries must not conflict with the if criterion.

regions(rlist) Use World Bank's 3-letter
region names to specify region aggregates for which results are
tabulated and, if graph options specified, displayed. Subject to the the
if criterion.

world Present tabulated results and, if graph options specified,
display global totals (or totals for all countries included by the
if criterion).

gr7 Display and save graphs in version 7's gr7
style: Fast but crude.

graph Display and save graphs in version 9.2 style:
Slow and elegant.

grcombine Combines all 3 or 4 graphs into the panels
of a single graph. User must also specify either gr7 or
graph graphing method.

grc1leg Alternative approach to combining graphs into panels
of a single graph such that all panels have a common legend.
User must also specify either gr7 or
graph graphing method.

norescale Unless this option is specified, the
numeric values on the vertical axes of all graphs are rescaled to powers
of 10 that assure that the labels of the tick marks are less than four
digits. (Variables are returned to their unscaled units before
aidsdif exits. Rescaling uses my rescale command, which must
be on the adopath.)

legend(legend_options) Not included in dialog
Legend suboptions are passed to the graph commands. Omitting the legend option
is the same as selecting legend(pos(9) ring(0)) so that
the legend appears on the left axis of the graph and inside its
boundaries. Useful suboptions include:

off suppresses the legend
ring(0) places legend inside the graph boundaries
pos(3) places legend on right of graph
size(small) reduces the size of legend text
span stretches the legend box horizontally

The following options work best with option graph, but
also influence the output when options gr7 and/or grcombine
are selected.

titles(titles_options) Replaces standard
title for "scenario" graphs. Specifying " " suppresses the title.

titled(titled_options) Replaces standard
title for "difference" graphs. Specifying " " suppresses the title.

titler(titler_options) Replaces standard
title for "ratio" graphs. Specifying " " suppresses the
title.

titleb(titleb_options) Replaces standard
title for cost-effectivness bar graphs. Specifying " " suppresses the
title.

subtitle(subtitle_options) Replaces
standard subtitle for all graphs. Specifying " " suppresses the
subtitle.

Additional graphing options (Output 2 tab)

grs Construct a graph for each analytical vairable which
displays the baseline and all scenario projections.

grd Construct a graph for each analytical vairable which
displays the difference between each scenario projection
and the baseline projection.

grre Display the ratio of the cost variable (cmd:costvar)
to the effect variable (cmd:benvar) for each year of the projection.

grcebyh Display the cost-effectiveness in the reference year
for each possible horizon year up to the last year of the projections.
This graph converges to the overall cost-effectiveness ratio in the last year
of the projection. It is useful for demonstrating the sensitivity of the
overall cost-effectiveness to the choice of the planning horizon.

gricer Display incremental cost-effectiveness ratio
or cost-benefit ratio
for each scenario relative to the baseline scenatio, with cost
on the vertical axis and effects or benefits on the horizontal axis.

nogrce Suppresses the default display of a bar graph comparing
the cost-effectivness of each scenario to the baseline scenatio.

Saving option

saving(filename, [replace]) Specifies the filename for
the projections data file which the program then saves in STATA's dta format. This name is also the stub of the filename for saved
graphics files. If saving(filename, [replace]) is omitted,
neither the data file of projections nor the *.gph files are saved.

Methods

The cost-effectiveness of Scneario X is defined by forming the
ratio of the present value of the incremental costs of Scenario X to the
present value of the incremental effects of that scenario. The present
value of costs is computed as the sum of the discounted stream of future
incremental costs, calculated by the program as difX_costvar.
The present value of effects or benefits is computed as the sum of the
discounted stream of future incremental effects , calculated by the
program as difX_benvar. Both costvar and benvar
must be "flow" variables, as opposed to stock variables or percentages.
If the present value of the incremental effects of a scenario is close
to zero, cost-effectiveness is not defined, so the program produces an
error.

Examples

The following example analyzes two projection runs previously
generated by aidsproj. The run which assumed a continuation of
the country-specific historical rate of uptake of antiretroviral
treatment (the file global_adjhist.dta) is designated the baseline
scenario. The run assuming rapid uptake (the file global_ajd95.dta) is
designated Scenario 1. The two analysis variables that are compared are
those for annual total costs (costtot)and annual deaths (d).
The only graph selected is the default one grce presenting the bar
chart showing the cost-effectiveness of Scenario 1 relative to the
Baseline. Option gr7 selects rapid graphing for speed of
execution. Option world requests that the analysis present the
weighted results for all countries in the input data.

aidsdif costtot d, bl(global_adjhist) s1(global_adj95) gr7 world

The following example adds another scenario, adds descriptive
names for all three scenarios, adds additional analytical graphs and
specifies output for two specific countries (Cote d'Ivoire and Burkina
Faso), for the region of Sub-Saharan Africa and for all countries. The
grcombine option specifies that individual graphs be combined as
the panels of a single graph. By setting pause on prior to
aidsdif's execution, the user has an opportunity to observe each
graph as it is produced.

pause on

aidsdif d costtot , graph grcombine grscenarios grdifferences grre ///
bl(global_adjhist) bl_name("Historical uptake with 5% decline in incidence") ///
s1(global_adj50) s1_name("50% uptake with 5% decline in incidence") ///
s2(global_adj95) s2_name("95% uptake with 5% decline in incidence") ///
region(ssa) countries(CIV BFA) world

pause off

Author

Mead Over,
Center for Global Development, Washington, DC 20036 USA. Email:
MOver@CGDev.Org if you observe any
problems.

References

Over, M., "Prevention Failure: The Ballooning Entitlement
Burden of U.S. Global AIDS Treatment Spending and What to Do About It"
Working Paper 144,
Center for Global Development, 2008.

Over, M., "Opportunities for presidential leadership on AIDS:
From an "Emergency Plan" to a Sustainable Policy," in N. Birdsall (ed.),
The White House and the World: A Global Development Agenda for the Next US President,
Center for Global Development, 2008, Chapter 11, pp. 299-326.

Over, M., "AIDS Treatment in South Asia: Equity and
Efficiency Arguments for Shouldering the Fiscal Burden When Prevalence
Rates Are Low"
Working Paper 161,
Center for Global Development, 2009.