ICE BOX PLOTTER
INCREMENTAL COST EFFECTIVENESS
NNT (Number Needed to Treat)
and CNT (Cost Needed to Treat)
Cost Effectiveness Ratios (ICE Ratios)
with Consideration of Confidence
Beta Version - for Testing
This calculator examines various clinical
and economic elements of treatment:
1) Number Needed to Treat (NNT) to attain
one additional good outcome.
2) Cost of treatment, upper and lower
3) Approximating Incremental cost-effectiveness
ratio (ICE Ratio) of treatment.
4) Confidence intervals considerations
on NNT and Cost Needed to Treat (CNT).
The relationship between treatment and
outcome is represented
in a 2 by 2 table, from which can be
measures of association.
[You can change values in white boxes and hit "calculate"]
Clinical Data (enter
values in blue boxes)
Economic Data (enter values in green
Incremental Cost Per Patient
RELATIVE RISK = RR =[a/(a+b)]/[c/(c+d)] >>>>
(Risk Ratio, Relative Risk)
ODDS RATIO >>>> OR = ad/bc
RELATIVE RISK REDUCTION
RRR = ( c/(c+d) - a/(a+b))/ (c/(c+d)) >>>>
RATE DIFFERENCE = RD
(ATTRIBUTAL RISK = AR) RD or AR = c/(c+d)-a/(a+b)
(Absolute Risk Change)
Outcome rates change
Due to treatment
group, for a change of >>>>>
= RD (or AR) =
Upper and Lower values of RD above are
based on 95% Confidence Interval = +/- =
= +/- Confidence Interval
NEEDED TO TREAT TO OBTAIN ONE EXTRA "SUCCESS".
NNT = 1/RD = 1/AR =
= 1/(c/(c+d)-a/(a+b)) =
= NNT =
TO TREAT TO OBTAIN ONE EXTRA "SUCCESS"
CNT = Incremental cost per patient *
= CNT =
Cost needed to treat to obtain one extra
which roughly estimates an Incremental
Cost Effectiveness (ICE Ratio).
Notes: A negative NNT value can indicate
that there is a chance that some patients could be harmed by the treatment.
If the upper and lower value of RD (AR)
passes through zero, then the NNT passes through infinity
and the difference in the two clinical
groups would not be considered statistically significant.
The default values entered in the clinical
boxes above, are roughly based on the percentages and therapy costs for
treating myocardial infarction patients
in the classic TPA vs. Streptokinase paper by D. Mark, NEJM 1995.
For simplicity, this ICE Box example
uses only 200 patients, while the Mark paper sample size total, based
the GUSTO study was 41,000 patients for
survival analysis and about 17,000 cases for economic analysis.
When a total of 20,000 patients are entered
into the clinical boxes above with the same success and failure rates,
the NNT confidence interval does not include a negative value or infinity.
In the Mark paper, patients successfully
treated were expected to live at least 5 years,
and the resulting incremental
cost-effectiveness ratio was about $40,000 per life year saved.
This published result is similar to our
default CNT divided by 5 years.
Thus if a larger numbers
of patients are entered into the default clinical boxes, the confidence
intervals should be more narrow.
The CNT values for one additional "Success"
outcome are similar to the incremental cost effectiveness ratio (ICE Ratio)
the ICE numerator and denominator are
related to the incremental costs divided by the incremental effects.
In this example, it is assumed that the
lower NNT limits had the lower costs and high NNT limits had higher costs,
but this may not always be the case.
You can change the entered cost values to explore different results.
-- Some of the NNT calculations are based
on materials developed by R. Hamm.
-- Confidence Interval calculations are
based on the method discussed
in the EBM Bandolier bulletin at www.jr2.ox.ac.uk/bandolier/band18/b18-9.html