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Economic Evaluation in Clinical Trials (revised 05/03/13)
Chapter 9: Confidence Intervals for CER, CI for NMB, and Acceptability Curves
This page contains 3 sets of programs for estimating confidence intervals for cost-effectiveness ratios,
confidence intervals for NMB, and acceptability curves.
One set of programs (iprogs.do) represent "immediate form" programs, in which you have already calculated
measures of incremental cost and QALYs, standard errors of cost and QALYs, and the correlation between cost and
QALYs. The programs use these data to calculate CI for CER, CI for NMB, and acceptability curves.
A second set of programs (uprogs.do) calculate CI for CER, CI for NMB, and acceptabilty curves based on
univariate t-tests of cost and QALYs.
The third set of programs (bsceaprogs.do) use an already constructed sample of incremental cost and QALYs
(e.g., 1000 replicates of the difference in mean cost and QALYs) to calculate CI for CER, CI for NMB, and
acceptabilty curves.
We provide data from the 3 hypothetical experiments that we presented in chapters 8 and 9 as examples for
these programs. For each experiment we provide a patient level dataset as well as a bootstrapped dataset.
Finally, we provide annotated log files for use with each of the three sets of programs.
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IPROGS.DO: "Immediate form" programs to estimate Fieller's method confidence intervals for
cost-effectiveness ratios (fielleri), confidence intervals for NMB (nmb1i and nmbi), and the acceptability curves (accept1i and accepti).
Also included is a program that defines the CI below which the lower limit is less than the upper limit; the CI
between which the lower limit is greater than the upper limit; and the largest defined CI (ciboundi). Third,
there is a program that uses univariate evaluation of means to calculate the inputs for these four immediate form
programs (ipinputs). Finally, the program called iprogsdoc provides brief documentation for the programs. All
programs are included in iprog.do.
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ceagraphs.do: Programs that when used in conjunction with fielleri, accepti, and nmbi graphically display the point estimate and confidence limits for the cost-effectiveness ratio (fiellergraph), the acceptability graph (accgraph), and the point estimate and confidence limits for NMB defined for varying levels of WTP (nmbgraph). The ceagraphsdoc program provides a brief overview of the programs and the syntax for running them.
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Three sample datasets, c8exper1.dta, c8exper2.dta, and c8exper3.dta are
provided. As in chapters 8 and 9, these experiments provide examples of pattern 1, 2, and 3 results, respectively.
Each dataset has 4 variables: id represents the participant ID number; the 0/1 treat represents treatment
group; cost equals the patients' cost and qaly equals the patients' QALYs. Finally, a log file (iprogslog.pdf) is
provided which demonstrates use of the programs. Programs particularly useful if one has estimated costs and
outcomes by use of tests other than the t-tests.
- Data
- UPROGS.DO: Programs that use t-tests to estimate Fieller's method confidence intervals for cost-effectiveness
ratios (fielleru), confidence intervals for NMB (nmbu), and the acceptability curves (acceptu). Also included is a
program that defines the CI below which the lower limit is less than the upper limit; the CI between which the lower
limit is greater than the upper limit; and the largest defined (ciboundu). Finally, uprogsdoc provides brief
documentation of the programs. All programs are included in uprog.do. The 3 sample datasets above can be used with
these programs as well. Finally, a log file (uprogslog.pdf) is provided which demonstrates use of the programs.
These programs are useful if one wants to estimate costs and outcomes by use of t-tests.
- BSCEAPROGS.DO: Programs to estimate confidence intervals for cost-effectiveness ratios (bscicer), confidence
intervals for NMB (bsnmb), and the acceptability curve (bsaccept) from bootstrapped estimates of cost and outcome.
bsceaprogsdoc provides brief documentation of the programs. All 4 programs are included in bsceaprogs.do. They
presume you have already constructed the bootstrap sample. Three sample datasets, c8bsexp1.dta, c8bsexp.dta, and
c8bsex3.dta, are provided. These datasets represent bootstrapped replicates of c8eper1 - c8cexper3, above. Readers
should understand that unless one bootstraps an estimate in the 1000s of times, it is unlikely that the bootstrapped
point estimates and standard errors will be precisely those we've described. They should also understand that we've
manipulated our bootstrapped examples so that with 1000 replicates, they have estimates that are nearly identical to
those we've reported in the chapter. Finally , a .log file (bsceaprogslog.pdf:) is provided which demonstrates use
of bscicer. bsnmb and bsaccept.
- BSCEAGRAPHS.DO:
Programs that when used in conjunction with bscicer, bsnmb, and bsaccept graphically display the point estimate and confidence limits for the cost-effectiveness ratio (bscicergraph), the acceptability graph (bsaccgraph), and the point estimate and confidence limits for NMB defined for varying levels of WTP (bsnmbgraph). The bsceagraphsdoc program provides a brief overview of the programs and the syntax for running them
- bsceagraphs.do: Stata .do file ( works with revised bsceaprogs.do only)
- Data
Updated 5/6/11
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