Strategic Purchasing and Commissioning

Why this matters in health economics

Someone holds the population's health money and pays it out to providers. Whether that someone — a national insurance fund, a ministry, a regional purchasing authority, a private insurer — spends the money actively or passively is one of the largest determinants of what a health budget buys. A passive purchaser reimburses claims and settles bills as they arrive, taking the volume, mix, and quality of care as given. A strategic purchaser decides in advance which services to buy, selects the providers most likely to deliver value, writes contracts that reward the right behaviour, and checks that it got what it paid for. The same budget, spent the second way, buys demonstrably more health.

The stakes are public money at very large scale, and the leverage is unusually direct. Purchasing is the point where a health system's abstract priorities become concrete transactions: a benefit package becomes a set of contracts, a strategy for chronic disease becomes a decision to fund community clinics rather than more hospital beds. Get purchasing right and scarce funds flow towards effective, equitable, well-run services; get it wrong and money follows habit, provider convenience, or the loudest lobby, while the services a population actually needs go unfunded. In most systems purchasing is also bound by statutory duties — to secure value for money, to procure fairly and transparently, to avoid conflicts of interest — so the discipline carries legal as well as economic weight.

Purchasing decisions are equity decisions in disguise. What a purchaser chooses to commission, and where it places the contracts, determines which populations are served well and which are underserved. A purchaser that buys only what is easy to count and easy to bill will systematically under-buy prevention, mental health, and care for complex patients whose value is real but diffuse. This chapter is about how a payer purchases; how the wider system is structured — the financing models and the payment mechanisms themselves — belongs to Chapter 3.1 — Health Systems, which this chapter assumes and cross-references rather than repeats.

Core concepts

The organizing distinction, drawn from the World Health Organization's (WHO) health-financing work, is between passive and strategic (or active) purchasing. The WHO frames strategic purchasing as the deliberate, evidence-based answer to three linked questions: what interventions and services to buy, from whom to buy them, and how to buy — including how providers are paid and at what price. A passive purchaser answers none of these actively; it pays for whatever is delivered. A strategic purchaser treats all three as choices to be made in the population's interest.

Commissioning is the practical expression of strategic purchasing, most developed in tax-funded systems such as England's National Health Service (NHS). It is usually described as a cycle: assess the health needs of a population; plan and prioritize the services to meet them; procure and contract with providers; and monitor and review what is delivered, feeding the results back into the next round. The cycle matters because purchasing done well is continuous, not a one-off tender: needs change, providers perform, and contracts must be adjusted in light of evidence.

Strategic purchasing presupposes a purchaser–provider split — a structural separation between the body that holds the money and buys care and the bodies that deliver it. England created such a split in 1991 through its NHS internal market, and has since reorganized the purchaser side repeatedly, from health authorities to Clinical Commissioning Groups (CCGs) and, from 2022, to Integrated Care Boards (ICBs). The split is what makes purchasing a distinct discipline; without it, money and delivery are fused and there is no arm's-length buyer to exercise judgement.

Purchasing is an instance of the principal–agent problem. The purchaser (principal) wants health outcomes for its population; the provider (agent) knows more about clinical practice, costs, and its own effort than the purchaser can observe. Contract theory supplies the tools for writing agreements under that asymmetry — and its central lesson is that contracts are inevitably incomplete: no document can specify every contingency, so what you can measure and enforce shapes what you actually get. The main contract forms trade risk between the parties: a block contract pays a fixed sum for a broadly defined service (the purchaser bears demand risk cheaply but weakly rewards activity); a cost-and-volume contract pays per unit up to a ceiling; and a cost-per-case contract pays for each patient (the provider bears little demand risk but the purchaser's cost rises with activity). Which payment mechanism sits inside the contract — capitation, fee-for-service, diagnosis-related groups (DRGs) — is a Chapter 3.1 — Health Systems question; this chapter is about choosing and governing the contract that carries it.

Several tools let a purchaser buy more selectively. Selective contracting narrows the network to providers that meet quality, volume, or price standards rather than paying any willing provider; it is the engine of American managed care. Value-based purchasing — closely tied to the broader idea of value-based health care — ties payment to measured quality and outcomes rather than volume alone. Outcome-based contracts go further, making some or all payment contingent on results achieved; a social impact bond is one financing wrapper for this idea, with investors bearing the risk that outcomes fall short. And the make-or-buy decision asks whether the purchaser should commission a service from an external provider — a form of outsourcing — or provide it in-house, or knit providers together through integrated care so that a single accountable entity manages a pathway.

Finally, purchasing runs on two supporting disciplines. Procurement — and its regulated public form, public procurement — is the process of competitively selecting and awarding contracts fairly and transparently. And health technology assessment (HTA) supplies the evidence on what is worth buying, feeding the "what to purchase" question with cost-effectiveness and budget-impact analysis.

Best practices

1. Purchase strategically: decide what you are buying before you decide who from. The first discipline is to move from paying for whatever arrives to specifying, in advance, the services your population needs and the value you expect. Start every purchasing round from the population's health needs and the interventions known to meet them, not from last year's contracts rolled forward. A purchaser that cannot say what health outcome a contract is meant to produce is not purchasing strategically, however competitive its tender.

2. Run the whole commissioning cycle, not just the procurement step. Assessment, planning, procurement, and monitoring are one loop; organizations that treat commissioning as "running a tender" do the glamorous middle step and neglect the ends. The needs assessment that precedes procurement decides whether you buy the right thing, and the monitoring that follows decides whether you keep buying it. Budget staff time and analytical capacity for the assessment and review phases, not only for the contract award.

3. Anchor purchasing in a genuine needs assessment, not in provider supply. What gets bought should follow from the epidemiology and unmet need of the population, adjusted for deprivation and demography, rather than from the historical footprint of existing providers. Supply-led purchasing entrenches yesterday's pattern of care and systematically under-buys services — prevention, mental health, community care — that have no incumbent lobby. Use routine data, HTA evidence, and clinical input to build a picture of need that is independent of who currently holds the contracts.

4. Choose the contract form to match demand uncertainty and where risk should sit. A block contract is cheap to administer and shields the purchaser's budget but weakly rewards activity and can hide under-provision; a cost-per-case contract sharpens the incentive to treat but exposes the purchaser to volume risk; cost-and-volume contracts sit between. Decide deliberately who should bear demand risk — the party better able to manage or absorb it — and pick the form accordingly, rather than defaulting to whatever is administratively familiar. Remember contracts are incomplete: pair any form with the monitoring that catches its characteristic gaming.

5. Match the payment mechanism inside the contract to the behaviour you want. Capitation rewards prevention and continuity but invites under-provision; fee-for-service rewards activity but invites over-provision; case-based payment such as DRGs rewards throughput but invites up-coding. The mechanisms themselves and their distortions are developed in Chapter 3.1 — Health Systems; the purchasing task is to select the mechanism that pushes providers towards the outcome you are buying and to blend mechanisms where a single one would distort.

6. Use selective contracting where quality or volume justifies it — and weigh the access cost. Narrowing the network to accredited, higher-volume, or better-value providers can raise quality and lower price, which is why managed care and centralized specialist commissioning rely on it. But selectivity has an equity price: a narrower network can mean longer journeys and reduced access for rural or disadvantaged patients. Concentrate services where the volume–outcome relationship is strong and the travel burden is tolerable, and be explicit about who bears the access cost.

7. Make the make-or-buy decision explicitly, and protect against hollowing out. Whether to provide a service in-house, outsource it, or integrate providers around a pathway is a strategic choice about capability, transaction costs, and control — not a default. Outsourcing can bring specialist skill and flexibility, but repeated outsourcing can erode the purchaser's own knowledge until it can no longer specify or judge what it buys, leaving it captured by its contractors. Keep enough in-house expertise to remain an intelligent client, whatever you decide to buy externally.

8. Design outcome-based contracts only where outcomes are measurable, attributable, and timely. Paying for results is powerful where the outcome is clearly defined, plausibly caused by the provider's effort, and observable within the contract period. Where outcomes are diffuse, confounded by factors outside the provider's control, or emerge only after years — as with much prevention — outcome-based payment invites cherry-picking of easy cases and gaming of the metric. Reserve it for well-specified problems, and combine a modest outcome element with a stable base payment rather than betting the whole contract on a single indicator.

9. Manage the contract after signing; award is the start, not the finish. Value is realized or lost during the contract, not at the tender. Build in performance monitoring, agreed data flows, regular review meetings, and defined remedies for under-performance, and use them. A purchaser that files the contract and looks again only at renewal has reverted to passive purchasing under a strategic-sounding name.

10. Guard against provider market power and concentration. In many areas a single hospital or provider group is effectively the only option, which turns "purchasing" into price-taking. Watch for concentration, resist mergers that would leave you without a credible alternative, and use the tools you have — benchmarking against comparable providers, the threat of re-tendering, collaborative purchasing with other payers — to keep a dominant provider honest. Germany's system illustrates the counterweight: sickness funds bargain collectively with provider associations, pooling purchasing power that no single fund could exert alone.

11. Keep transaction costs proportionate to the value at stake. Purchasing is not free: tendering, contracting, monitoring, and litigation all consume resources, and an elaborate competitive process for a small or low-risk service can cost more than it saves. Match the intensity of the procurement to the size and risk of the contract — light-touch for stable, low-value services; full competition and rich monitoring for large, contestable, high-risk ones. The internal-market experience in several countries is that transaction costs can quietly swallow the efficiency gains competition was meant to deliver.

12. Build the purchasing capability the strategy assumes. Intelligent purchasing needs analysts who can read population data, clinicians who can specify quality, contract managers who can hold providers to account, and legal skill to procure lawfully. Many purchasers adopt the language of strategic purchasing without the workforce to practise it, and revert to passive reimbursement under pressure. Invest in data, analytics, and skilled commissioners deliberately, because the discipline is only as good as the people who run it.

Questions to discuss with your team

1. Are we actually purchasing the health our population needs, or are we paying for the activity our providers already produce? This question tests whether your commissioning is strategic or passive in substance rather than in name. Trace a major contract back to its origin: did it start from an assessment of population need, or from last year's contract uplifted for inflation? The honest answer is usually mixed — some services are genuinely commissioned against need, while others persist because an incumbent provides them and no one has re-examined the case. The tension is that shifting money towards under-served needs means shifting it away from an existing provider and its patients, which is politically and operationally hard. A good discussion names one or two services you are buying out of habit rather than need, and what it would take to redirect that money.

2. Where should we make versus buy, and what capability would we quietly lose by outsourcing? Make-or-buy looks like a procurement question but is really a strategic one about what your organization must be able to do itself. Pick a service currently provided in-house that could be outsourced, and one currently outsourced that could be brought back, and work through the transaction costs, the specialist skill, and the control each option gives up. The real tension is between the short-term efficiency of buying a service and the long-term risk of losing the expertise to specify, judge, or ever re-provide it — the slow slide from intelligent client to captured client. An honest answer distinguishes services where the market is genuinely competitive and reversible from those where outsourcing would leave you dependent on a provider you can no longer replace, and keeps enough in-house knowledge to remain a credible buyer either way.

3. Do we have the information and the market power to be an intelligent purchaser, or are we a price-taker to a dominant provider? Strategic purchasing assumes a real choice of providers and enough information to judge them; in much of health care neither holds. Ask, for your largest contracts, how many credible alternative providers exist and how good your data on quality and cost really is. The uncomfortable answer is often that a single hospital or group is effectively unavoidable and that you know far less about its performance than it knows about itself — the principal–agent problem at full strength. The tension is that building countervailing power (collaborative purchasing, benchmarking, credible re-tendering) and better information both cost money and provoke providers you depend on. A candid discussion identifies where your purchasing is strongest and weakest, and which one improvement — better outcome data, a collaborative purchasing arrangement, a genuine second provider — would most shift the balance towards you.

4. Do we run the whole commissioning cycle, or do we lavish attention on the tender and neglect the assessment before and the management after? Commissioning is a loop — assess, plan, procure, monitor — but the procurement step is the visible, deadline-driven one, so it tends to absorb the analytical and legal effort while the ends are under-resourced. Pick one recent contract and ask honestly how much staff time went into the needs assessment that shaped it and the performance management that followed, versus the competition itself. The tension is that assessment and monitoring have no hard deadline and no adrenaline, so they are the easiest work to defer when the team is stretched, yet they are precisely what decides whether you bought the right thing and kept getting it. An honest answer will usually admit that at least one phase is done thinly or not at all, and will name what capacity — analysts, data flows, review meetings — it would take to close the loop rather than just run tenders well.

5. Where are we paying for outcomes, and are those outcomes actually measurable, attributable, and timely — or are we inviting gaming? Outcome-based and value-based contracting sound unambiguously good, but they only work where the result is clearly defined, plausibly caused by the provider's effort, and observable within the contract period. Take any contract with a performance or outcome element and interrogate each indicator: could the provider improve the number by selecting easier patients, coding differently, or shifting effort from unmeasured to measured care? The tension is that the outcomes that matter most — preventing disease, managing complex patients well — are often the hardest to attribute and the slowest to appear, so the metrics that are easy to pay against are rarely the ones you most want to buy. A candid discussion distinguishes the contracts where outcome payment is genuinely earning its keep from those where it is cosmetic or actively distorting, and confirms that a stable base payment sits beneath any outcome element rather than the whole contract riding on one indicator.

6. When we contract selectively for quality or price, who bears the access cost, and have we said so out loud? Narrowing the network to accredited, higher-volume, or better-value providers can genuinely raise quality and lower price, but selectivity always has a distributional edge: someone travels further, waits longer, or loses a local service. Identify a service where you have concentrated provision, or are considering it, and ask which populations — rural, elderly, deprived, without transport — carry the access burden that the quality gain is bought with. The tension is that the volume–outcome case for concentration and the equity case for local access are both legitimate and frequently point in opposite directions, and the losers are usually less organized than the incumbents whose closure the concentration implies. An honest answer names the trade-off explicitly, sets an access floor for the populations who would otherwise be stranded, and treats "who pays the access cost" as a decision to be made openly rather than a side effect to be discovered later.

In practice: a health economics example

The fictional middle-income country of Solara funds health care through a national insurance fund, the Solara Health Insurance Agency, which for years has paid providers passively: any accredited clinic or hospital submits claims for services rendered, and the agency reimburses them at a national fee schedule. Spending on kidney dialysis for chronic kidney disease (CKD) has grown far faster than the budget, driven by a proliferation of small private dialysis centres billing per session. An audit finds wide variation in quality between centres, several billing for sessions of doubtful necessity, and poor management of the underlying diabetes and hypertension that drive patients onto dialysis in the first place. The agency's board asks its health-economics team to move from passively paying dialysis claims to strategically purchasing kidney care.

The team reframes the problem through the commissioning cycle. The needs assessment shows that CKD is concentrated among poorly controlled diabetic and hypertensive patients, that early detection and management could slow progression, and that dialysis capacity is unevenly distributed — oversupplied in the capital, scarce in rural provinces. Passive per-session reimbursement has rewarded exactly the wrong things: building dialysis chairs where patients are easy to bill, and treating end-stage disease rather than preventing it. What the population needs is a pathway — detection, upstream management, and high-quality dialysis where dialysis is genuinely required — not simply more sessions.

The team designs a strategic purchase in three parts. First, selective contracting for dialysis: rather than paying any accredited centre, the agency will contract only centres meeting defined clinical standards, minimum volumes, and outcome reporting, concentrating provision enough to raise quality while setting a rural-access floor so that selectivity does not strand remote patients. Second, a contract form deliberately chosen — a capped cost-and-volume contract per accredited centre, with a bundled tariff covering a patient's dialysis and routine monitoring rather than paying per isolated session, so the incentive to inflate session counts disappears. Third, an outcome-based element, modest and carefully bounded: a small share of payment tied to measurable, attributable indicators — vascular-access infection rates and the proportion of patients whose CKD is managed to guideline targets — with the bulk of payment stable, so providers are not gaming a single metric or shunning complex patients.

The team is candid with the board about the tensions. Selective contracting will close some low-volume private centres, which is contested locally even where quality is poor. The bundled tariff shifts demand risk onto providers, who will resist unless the price is credible, so the agency must invest in costing data it does not yet fully hold. And the deepest problem — preventing CKD upstream — cannot be solved by purchasing dialysis better; it needs the agency to commission diabetes and hypertension management in primary care, a separate and longer purchase whose benefits arrive years later and are hard to attribute. The team recommends a make-or-buy judgement too: rather than outsource the whole kidney pathway to a single large operator, which would leave the agency dependent on one provider, it keeps pathway design and monitoring in-house and buys the delivery competitively. The board accepts the redesign and, crucially, funds a commissioning team to manage the contracts actively — an acknowledgement that strategic purchasing is a standing capability, not a one-off tender. Thailand's National Health Security Office (NHSO), which purchases strategically for a national coverage scheme and negotiates hard on price and inclusion, is the real-world reference point the team cites for what an active national purchaser can achieve.

Four sector lenses

Startup

A health-technology or clinical start-up is usually on the selling side of the purchasing relationship, and its survival depends on understanding how its buyer purchases. A venture offering, say, a CKD risk-stratification tool must know whether the purchaser buys against outcomes it can influence, whether there is a contract vehicle and budget line for a new service at all, and who captures the saving it creates. Small commissioning functions — a start-up health plan, a new regional purchaser — face the opposite challenge: they must purchase strategically without the data, market power, or contract-management staff a mature payer takes for granted, and are tempted to reimburse passively because it is administratively simpler. The discipline for both is to be specific about the value exchanged and realistic about the thin capability available to govern it.

Small business

A small but established provider — a general-practice partnership, a single-site dialysis clinic, a physiotherapy practice, a niche equipment supplier — meets strategic purchasing from the receiving end, as the holder of a contract rather than the writer of one. Unlike a start-up, it is not chasing its first deal or its next funding round; it has a steady book of work, a known cost base, and a reputation to protect, so its concern is the terms on which it is bought: whether a block contract leaves it carrying unfunded demand, whether a bundled tariff is priced against real costs, and whether it can meet the volume, accreditation, and reporting thresholds that selective contracting imposes. Its bargaining power is modest — it cannot exit the way a large group can, and a single lost contract may be existential — so it competes on quality, responsiveness, and local knowledge rather than scale, and it feels the equity edge of concentration directly when a purchaser routes volume to bigger providers. The discipline for a small established provider is to know its own costs well enough to negotiate a credible price, to keep its accreditation and outcome data in order so it survives a tightening of standards, and to collaborate with peers where joint bidding or shared back-office capacity lets it compete for work it could not win alone.

Enterprise

A large insurer, hospital group, or integrated-care organization purchases at a scale that makes it a market-maker. It runs formal procurement functions, negotiates network contracts, operates value-based and selective-contracting arrangements, and has the analytics to segment its population and monitor providers in detail. At this scale the organization can genuinely shape provider behaviour — steer volume to preferred providers, impose quality standards, share risk through bundled and capitated contracts — but it also attracts regulatory scrutiny for market power and for whether its selectivity restricts access unfairly. The strategic question for an enterprise purchaser is whether it is using its scale to buy value for its population or merely to extract price, and whether its contract management is real or nominal.

Government

Government is the archetypal strategic purchaser, whether through a national insurance fund, a ministry, or regional commissioning bodies, and it purchases under statutory procurement law and public accountability that private buyers do not face. Its comparative advantage is reach and countervailing power: a national purchaser such as Thailand's NHSO or a German sickness-fund association can negotiate prices, define benefit packages, and impose quality conditions across an entire system, pooling the purchasing power to face down concentrated providers. Its discipline must match that reach — transparent procurement, conflict-of-interest management, and enough in-house capability to remain an intelligent client rather than a captured one. The WHO's strategic-purchasing agenda is aimed squarely at governments and national funds, urging them to move from passive reimbursement towards active, evidence-based buying as a route to universal health coverage.

Common failure modes

• Passive purchasing dressed as strategic. Adopting the language of commissioning while, in substance, reimbursing whatever providers deliver. Fix: start every purchase from population need, and check that each major contract can name the outcome it buys.

• Procurement without the rest of the cycle. Running a competitive tender but skipping the needs assessment before and the contract management after. Fix: resource the assessment and monitoring phases as deliberately as the award.

• Set-and-forget contracting. Awarding a contract and looking again only at renewal, so under-performance goes unremarked for years. Fix: build in monitoring, data flows, review meetings, and remedies, and use them.

• Outcome-based contracting where outcomes cannot be measured or attributed. Paying for results that are diffuse, confounded, or slow to appear, inviting cherry-picking and metric-gaming. Fix: reserve outcome payment for well-specified, attributable, timely results, and keep the base payment stable.

• Selectivity that strands the disadvantaged. Narrowing the provider network for quality or price without accounting for the access cost to rural and deprived populations. Fix: concentrate services only where the volume–outcome case is strong, and set an explicit access floor.

• Hollowing out the intelligent client. Outsourcing so much that the purchaser can no longer specify or judge what it buys, and becomes captured by its contractors. Fix: retain enough in-house clinical, analytical, and contracting expertise to remain a credible buyer.

• Ignoring provider market power. Purchasing as if a real choice existed where one dominant provider makes the payer a price-taker. Fix: benchmark, purchase collaboratively, and keep a credible alternative or re-tendering threat alive.

• Transaction costs that swallow the gains. Elaborate competition and monitoring for services too small or stable to justify them. Fix: scale the procurement's intensity to the contract's value and risk.

Maturity model

Checklist

• State, for each major contract, what population need it meets and what outcome it is meant to buy.
• Run the full commissioning cycle — assess, plan, procure, monitor — and resource the assessment and monitoring phases, not only the award.
• Base what you purchase on a needs assessment independent of the current provider footprint.
• Choose each contract form (block, cost-and-volume, cost-per-case) deliberately, deciding who should bear demand risk.
• Match the payment mechanism inside the contract to the behaviour you want (cross-referencing Chapter 3.1 — Health Systems).
• Where you contract selectively, set an explicit access floor for rural and disadvantaged populations.
• Make every make-or-buy decision explicitly, and confirm you retain enough in-house expertise to remain an intelligent client.
• Use outcome-based payment only where outcomes are measurable, attributable, and timely, over a stable base payment.
• Put performance monitoring, data flows, review meetings, and remedies into every contract — and use them.
• Assess provider market power on your largest contracts and maintain a credible alternative, benchmark, or collaborative-purchasing counterweight.
• Scale the intensity of procurement and monitoring to each contract's value and risk.
• Confirm you have the analysts, clinicians, and contract managers the strategy assumes.

Key sources

• World Health Organization — health financing and strategic purchasing guidance (moving from passive to strategic purchasing for universal health coverage).
• The King's Fund and NHS England — the commissioning cycle and the experience of Clinical Commissioning Groups and Integrated Care Boards in England.
• OECD — Health at a Glance and Better Ways to Pay for Health Care — comparative evidence on provider payment and purchasing.
• Robert Robinson & Josep Figueras (eds.), European Observatory on Health Systems and Policies — Purchasing to Improve Health Systems Performance.
• Thailand's National Health Security Office (NHSO) — a widely cited national exemplar of strategic purchasing in a middle-income setting.
• Economics Network, Health Economics for Teachers — health systems and policy modules — https://economicsnetwork.ac.uk/health/teachers

References

1. Commissioning — Wikipedia — https://en.wikipedia.org/wiki/Commissioning
2. NHS internal market — Wikipedia — https://en.wikipedia.org/wiki/NHS_internal_market
3. Principal–agent problem — Wikipedia — https://en.wikipedia.org/wiki/Principal%E2%80%93agent_problem
4. Contract theory — Wikipedia — https://en.wikipedia.org/wiki/Contract_theory
5. Managed care — Wikipedia — https://en.wikipedia.org/wiki/Managed_care
6. Value-based health care — Wikipedia — https://en.wikipedia.org/wiki/Value-based_health_care
7. Social impact bond — Wikipedia — https://en.wikipedia.org/wiki/Social_impact_bond
8. Outsourcing — Wikipedia — https://en.wikipedia.org/wiki/Outsourcing
9. Integrated care — Wikipedia — https://en.wikipedia.org/wiki/Integrated_care
10. Procurement — Wikipedia — https://en.wikipedia.org/wiki/Procurement
11. Public procurement — Wikipedia — https://en.wikipedia.org/wiki/Public_procurement
12. Health technology assessment — Wikipedia — https://en.wikipedia.org/wiki/Health_technology_assessment
13. World Health Organization — Strategic purchasing for universal health coverage (health financing) — https://www.who.int/teams/health-systems-governance-and-financing/health-financing
14. European Observatory on Health Systems and Policies — Purchasing to Improve Health Systems Performance (Figueras, Robinson & Jakubowski, eds.) — https://eurohealthobservatory.who.int/publications/m/purchasing-to-improve-health-systems-performance
15. OECD — Health at a Glance — https://www.oecd.org/health/health-at-a-glance/
16. Economics Network — Health Economics for Teachers — https://economicsnetwork.ac.uk/health/teachers