Definition and Characteristics of Interventions
The object of a CEA—the thing to which it is applied, the costs and outcomes of which are to be analyzed—is an intervention. An intervention is an activity using human, physical, and financial resources in a deliberate attempt to improve health by reducing the risk, duration, or severity of a health problem (Jamison 2002, table 2). The term usually refers to an activity undertaken by a health system rather than by an individual. The emphasis on a deliberate, systemic effort means that an intervention is not simply anything that improves health; for example, if more rainfall leads to higher crop yields and better nutritional status, the rain does not count as an intervention. Similarly, although breastfeeding protects infants' health, it is not itself an intervention as the word is used in this volume. In contrast, a program to encourage new mothers to breastfeed is an intervention (as described in chapter 27). How effective such a program is, of course, depends on how many mothers it persuades to adopt the practice when they are neither currently breastfeeding nor planning to do so.
Interventions can be directed against an injury or disease (such as trachoma), a condition associated with or deriving from a disease (such as blindness), or a risk factor that makes the disease or condition more likely (such as the lack of hygiene that leads to trachoma). An intervention may pursue primary prevention at the population level—promoting personal behavior change, controlling environmental hazards, or delivering a medical intervention such as immunization to a large population—or individual action for primary prevention, cure, acute management, chronic management, secondary prevention, rehabilitation, or palliation. Box 15.1 defines these terms, and the figure in the box illustrates how interventions may prevent ill health events or deal with their consequences. Characterizing an intervention fully also means distinguishing the level at which it is delivered (home, primary care facility, district hospital, or referral hospital); indicating whether it involves drugs, immune enhancement, surgery, or physical or psychological therapy; and determining whether it requires a physician or uses diagnostic, laboratory, or imaging procedures. Such procedures are most often evaluated relative to the interventions they screen for or lead to, because they produce no health gain by themselves (although the information they provide can be valuable for reassurance or for promoting behavioral changes).
[Box 15.1]
An intervention in the everyday sense includes such activities as immunizing a child, performing a surgical procedure, or treating an infection with antibiotics. The authors of some chapters use the term only in this sense—for example, in discussing interventions that contribute to meeting the Millennium Development Goals (chapter 9). Authors of other chapters use the term in several other senses as well. It can mean modifying an existing intervention—for example, adding Haemophilus influenzae type B (Hib) antigen to the Expanded Program on Immunizations (EPI). Immunization against Hib is itself an intervention, but instead of analyzing it separately, one can use CEA to evaluate the additional cost of incorporating that antigen and the additional health gain that is expected to result (see chapter 20). The intervention studied is then not Hib immunization as such but the change in the full vaccination procedure. A change in the scale of an existing activity can also be considered an intervention, even if the activity itself is unchanged: that is, one can analyze the change in costs and in outcomes associated with expanding or contracting the coverage of the activity—for example, extending antiretroviral treatment for HIV and AIDS to a larger population (chapter 18) or screening more newborns for sickle cell anemia (chapter 34). In most chapters, the authors assume that expansion affects costs and outcomes linearly, so that the CER does not change. The chapters on vaccine-preventable diseases (chapter 20) and malaria (chapter 21) provide explicit estimates of the differential costs of expanding coverage.
Adding one intervention to another to deal with the same disease or condition is also an intervention, and combinations of interventions can be analyzed to determine which is most cost-effective or how the cost-effectiveness of one intervention depends on the other activities with which it is combined. Examples include successively adding drugs for treatment of epilepsy (chapter 32) or secondary prevention of cardiovascular disease (chapter 33) or combining several quite different interventions to control tobacco addiction or alcohol (chapters 46 and 47, respectively). The analyses of community health and nutrition programs (chapter 56) and integrated management of infant and childhood illness (IMCI; chapter 63) define "the intervention" as a whole program incorporating several different activities. Generally, even less empirical evidence exists concerning combinations of interventions than for individual activities, but IMCI is an exception; it has been evaluated more thoroughly than most single interventions.
Box 15.2 includes a more detailed discussion, using a hypothetical example of three different ways to deliver immunization, of how CEA can be applied to four of the meanings of intervention used here: an existing intervention at its current coverage, changes in the scale of that intervention, the addition of one intervention to another when expanding coverage, and the complete shift from one intervention to a different (and more cost-effective) one.
[Box 15.2]
Depending on the comparison undertaken, the result may be an average cost-effectiveness ratio (ACER) or an incremental cost-effectiveness ratio (ICER). The former compares total costs and total results, starting from zero, whereas the latter compares additional costs and additional results, starting from the current or some other level of coverage of an intervention.
Either shifting completely from one intervention to another or partially replacing one with another may reduce costs while producing more health gain. For example, if spending is high on hospitalization for acute myocardial infarction, a program using a "polypill" (several medications in a single pill) would reduce expenditures by lowering incidence (chapter 33) and would be cost saving, because less hospitalization would be needed. If the status quo is no hospitalization (as is typical at low incomes), a polypill program increases costs but may more than correspondingly increase health gains and therefore be more cost-effective. If the polypill both reduces costs and improves outcomes compared with hospitalization, it is said to dominate a hospital-only strategy. The second figure in box 15.2 illustrates the concept of dominance; table 45.4 and box 45.1 of chapter 45 provide examples of interventions that are dominated by others.
Unfortunately, reliable information on current intervention coverage, costs, and results is not always available even in high-income countries (iMTA 2005) and is extremely scarce in low-and middle-income countries. Studies showing whether an intervention is effective or cost-effective seldom cover the entire potential beneficiary population, and service provision in the private sector is often not recorded. Many chapter authors describe only the ACER of an existing or potential intervention, whereas others explicitly compare alternatives to current practice (for an example, see chapter 16).
Many of the activities analyzed here aim at promoting changes in personal behavior, by informing and persuading individuals to eat differently, to avoid smoking and excessive alcohol, to reduce the risks of sexually transmitted infections, or to practice better hygiene. Such efforts can be considered interventions in themselves, and as such are crucial for controlling HIV and AIDS (chapter 18), promoting better infant and child care (chapters 20 and 27), preventing inherited disorders (chapter 34), encouraging healthful diets and exercise (chapters 44 and 45), and avoiding addiction (chapters 46-48). But they can also be used to improve the effectiveness of other interventions by increasing awareness and demand, combating mistaken beliefs about diseases and risks, or reducing anxiety and stigma. In that sense, information, education, and communication delivered to consumers or providers or both are examples of policy instruments. They can facilitate or promote the use of such interventions as condom distribution, screening for diseases or congenital disorders, prenatal care, or immunization.
Other activities that can be classified either as interventions or as policy instruments include the following:
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Measures to increase the quality of care, such as some kinds of staff training or the introduction of better recordkeeping. These activities may simultaneously affect a large number of specific interventions in a health facility (chapter 70).
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Legislation and regulation to impose an intervention (for example, limiting the salt content of foods, chapter 45, or requiring that salt be iodized, chapter 28); to limit or prohibit an intervention that is ineffective or dangerous or to reduce unhealthful behavior such as smoking and excessive drinking (chapters 46-47); or to codify how an intervention should be delivered and determine who may provide it, as by licensing doctors, nurses, and health facilities (chapter 71).
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Economic incentives, which can take the form of subsidies or taxes (chapter 11) for particular items of consumption other than health goods or services, such as tobacco and alcohol (chapters 46-47) or condoms to reduce HIV transmission (chapter 18), or can be provided through protection of property rights, as for patented drugs (chapter 72).
These activities of informing, mandating, legislating, regulating, and taxing or subsidizing, which are at one remove or more from medical interventions, are also often called functions of the health system (WHO 2000, chapter 2; see also chapter 9 in this volume). Several of these instruments may be used together, such as increased taxes on tobacco or alcohol along with measures to educate consumers and to restrict the times, places, or quantities of consumption. Sometimes the instrument is needed before introducing or expanding an intervention to overcome barriers to its use or to make it cost-effective enough to be worth pursuing. Educating the affected population, for example, is crucial to screening and treatment of cancers and hemoglobin disorders. The need for a particular instrument may vary from country to country even if the intervention that it facilitates is identical, because the legal, regulatory, or financial environment differs.
