Net Health Benefit

Net health benefit

Net health benefit (NHB) expresses the value of a healthcare option in units of health by subtracting the health opportunity cost of its expected costs from its expected health outcomes. It provides a health-unit form of the net-benefit framework and can be used to compare alternatives at a stated cost-effectiveness threshold.

NHB is threshold-dependent. The threshold determines how monetary costs are converted into health-equivalent units, so changing the threshold can change the NHB of an option and which alternative has the highest net benefit.

How net health benefit is calculated

For healthcare option j:

NHBⱼ = Eⱼ − (Cⱼ ÷ λ)

where:

• Eⱼ is the expected health outcome for option j;
• Cⱼ is the expected cost of option j; and
• λ is the stated cost-effectiveness threshold expressed as cost per unit of health outcome.

When outcomes are measured in QALYs and λ is expressed as cost per QALY, dividing cost by λ converts monetary cost into health-equivalent units. The result is therefore expressed in QALYs or the corresponding health-outcome unit.

NHB should be calculated using costs and outcomes that refer to the same population, perspective, comparator set, time horizon, price basis and analytical assumptions.

Net health benefit and incremental net health benefit

Net health benefit and incremental net health benefit are related but distinct quantities.

NHB is calculated separately for each option:

NHBⱼ = Eⱼ − (Cⱼ ÷ λ)

Incremental net health benefit (INHB) compares two options:

INHB = NHBnew − NHBcomparator

which is equivalent to:

INHB = ΔE − (ΔC ÷ λ)

A positive INHB means the new option has greater net health benefit than the comparator at the stated threshold. A negative INHB means the comparator has greater net health benefit.

The distinction matters when several alternatives are evaluated because each option can be assigned its own NHB and the alternatives can then be ranked directly.

How NHB is used with several alternatives

When several mutually exclusive healthcare options are available, calculate NHB for every feasible option using the same threshold and analytical assumptions.

The option with the highest expected NHB is favoured on cost-effectiveness grounds at that threshold.

This does not mean that the option must be adopted. Affordability, equity, feasibility, implementation, evidence quality and other institutional considerations may affect the final decision.

Relationship between NHB and NMB

Net health benefit and net monetary benefit express the same net-benefit framework in different units.

For option j:

NHBⱼ = Eⱼ − (Cⱼ ÷ λ)

and:

NMBⱼ = (λ × Eⱼ) − Cⱼ

When λ is positive and the same threshold and analytical assumptions are used, NHB and NMB produce the same ranking of alternatives.

NHB expresses the result in units of health.

NMB expresses the result in monetary units.

The choice between them therefore depends largely on which scale is most useful for analysis, communication and decision-making.

Relationship between NHB and the ICER

For a two-option comparison in which the new intervention is more costly and more effective, the conventional ICER decision rule can be rearranged into an incremental net-health-benefit rule.

If:

ICER = ΔC ÷ ΔE

then the intervention is favoured on cost-effectiveness grounds at threshold λ when:

ΔE − (ΔC ÷ λ) > 0

or:

INHB > 0

Net health benefit avoids some of the interpretive difficulties of ratios because it remains a linear measure when incremental effects approach zero or when ICER signs become ambiguous.

How the cost-effectiveness threshold affects NHB

The threshold determines how much health is treated as being displaced by additional expenditure.

For a positive threshold:

Health-equivalent cost = C ÷ λ

A lower threshold converts a given cost into a larger health-equivalent amount, reducing NHB.

A higher threshold converts the same cost into a smaller health-equivalent amount, increasing NHB.

The threshold should be stated with its:

• value;
• currency;
• price year;
• health-outcome unit;
• jurisdiction or decision context;
• source; and
• institutional interpretation.

The threshold should not automatically be described as willingness to pay. Depending on the decision framework, it may represent a demand-side valuation, a supply-side opportunity-cost estimate, an institutional benchmark or another decision rule.

Worked example

Consider two options evaluated using a threshold of £20,000 per QALY.

Current care

• Expected cost: £10,000
• Expected QALYs: 4.50

NHB = 4.50 − (£10,000 ÷ £20,000) = 4.00 QALYs

New intervention

• Expected cost: £14,000
• Expected QALYs: 4.80

NHB = 4.80 − (£14,000 ÷ £20,000) = 4.10 QALYs

The new intervention has the higher NHB.

The same result can be expressed incrementally:

ΔC = £4,000

ΔE = 0.30 QALYs

INHB = 0.30 − (£4,000 ÷ £20,000) = 0.10 QALYs

The positive INHB means that the new intervention provides 0.10 additional net QALYs per patient relative to current care at the stated threshold.

Using the same example:

INMB = (£20,000 × 0.30) − £4,000 = £2,000

The INHB and INMB results give the same ranking because:

INMB = λ × INHB

NHB and health opportunity cost

NHB can make the health-opportunity-cost interpretation of a cost-effectiveness threshold particularly transparent.

When additional healthcare expenditure displaces other healthcare activity, dividing incremental cost by an opportunity-cost threshold estimates the health that may be forgone elsewhere in the system.

The incremental health gain from the intervention can then be compared with this health-equivalent cost:

INHB = incremental health gained − health-equivalent cost

A positive result indicates that expected health gained exceeds the health-equivalent cost represented by the threshold.

This interpretation depends on the meaning and empirical basis of the threshold being used. A threshold should not be assumed to measure health opportunity cost unless that interpretation is appropriate to the decision framework.

NHB and uncertainty

NHB is useful in uncertainty analysis because costs and outcomes are transformed into a single linear health-unit quantity at each threshold.

In probabilistic sensitivity analysis, NHB can be calculated for every option in every simulation.

For simulation s and option j:

NHBⱼ,s = Eⱼ,s − (Cⱼ,s ÷ λ)

These simulation results can be used to estimate:

• expected NHB for each option;
• expected incremental NHB;
• the probability that each option has the highest net benefit;
• cost-effectiveness acceptability curves; and
• quantities used in value-of-information analysis.

Probability of cost-effectiveness and expected NHB answer different questions. The option that most frequently has the highest NHB across simulations is not necessarily the option with the highest expected NHB.

Expected net health benefit

When costs and outcomes are uncertain, decision-making can compare the expected NHB of the available options.

For option j:

Expected NHBⱼ = E[Eⱼ − (Cⱼ ÷ λ)]

The option with the highest expected NHB is favoured on expected cost-effectiveness grounds at the stated threshold.

Expected NHB accounts for the magnitude of possible net-health gains and losses rather than only the probability that an option ranks first.

NHB and dominance

Net health benefit provides a consistent health-unit comparison across alternatives, but analysts should still examine the underlying costs and outcomes.

An option that is less costly and more effective than another strictly dominates it. That relationship should remain visible rather than being hidden behind a net-benefit summary.

Fully incremental analysis is also useful when several mutually exclusive alternatives are compared because it identifies the efficient set and extended dominance.

NHB complements these methods rather than replacing the need to understand the underlying cost-effectiveness structure.

NHB does not measure affordability

Positive NHB or the highest NHB does not establish that an intervention is affordable.

NHB evaluates comparative value at a stated threshold. Budget impact analysis estimates the financial consequences of adoption for a particular budget holder over a specified period.

An intervention can have the highest expected NHB while still creating substantial expenditure pressure.

NHB does not make the final decision

Net health benefit summarises expected health and costs under a stated threshold and analytical framework. It does not incorporate every consideration relevant to healthcare decisions.

NHB does not by itself determine:

• affordability;
• equity;
• implementation feasibility;
• organisational impact;
• evidence quality;
• distribution of health gains and costs;
• ethical considerations; or
• the final reimbursement or adoption decision.

These considerations may be addressed separately within health technology assessment or another decision process.

Common mistakes and how to avoid them

• Do not use NHB and INHB as though they are identical quantities.
• Do not calculate option-level NHB using incremental costs and effects.
• Do not assume that every cost-effectiveness threshold represents health opportunity cost.
• Do not describe λ automatically as willingness to pay.
• Do not compare NHB values calculated using different thresholds, populations, perspectives, horizons or price bases without adjustment.
• Do not interpret positive INHB as proof of affordability or automatic adoption.
• Do not select the option with the greatest probability of cost-effectiveness when the decision criterion is greatest expected NHB.
• Do not hide dominance or important cost-and-outcome differences behind a single summary statistic.
• Do not report NHB without stating the threshold used.

What should be reported

Report the alternatives, population, perspective, time horizon, costs, outcomes, threshold value and interpretation, currency and price year, discounting, option-level NHB, incremental NHB where relevant, uncertainty methods, expected NHB, probability-based results where used, assumptions, limitations and the distinction between cost-effectiveness and the wider decision.