Economic epidemiology
Encyclopedia
Economic epidemiology is a field at the intersection of epidemiology
and economics
. Its premise is to incorporate incentives for healthy behavior and their attendant behavioral responses into an epidemiological context to better understand how diseases are transmitted. This framework should help improve policy responses to epidemic
diseases by giving policymakers and health-care providers clear tools for thinking about how certain actions can influence the spread of disease transmission. The main context through which this field emerged was the idea of prevalence-dependence, or disinhibition
, which suggests that individuals change their behavior as the prevalence of a disease changes. However, economic epidemiology also encompasses other ideas, including the role of externalities, global disease commons and how individuals’ incentives can influence the outcome and cost of health interventions. Strategic epidemiology is a branch of economic epidemiology that adopts an explicitly game theoretic
approach to analyzing the interplay between individual behavior and population wide disease dynamics.
is a population-level phenomenon, but decisions to prevent or treat a disease are typically made by individuals who may change their behavior over the course of an epidemic, especially if their perception of risk
changes depending on the available information on the epidemics – their decisions will then have population-level consequences. For example, an individual may choose to have unsafe sex
or a doctor may prescribe antibiotics to someone without a confirmed bacterial infection
. In both cases, the choice may be rational from the individual’s point of view but undesirable from a societal perspective.
Limiting the spread of a disease at the population level requires changing individual behavior, which in turn depends on what information individuals have about the level of risk. When risk is low, people will tend to ignore it. However, if the risk of infection is higher, individuals are more likely to take preventive action. Moreover, the more transmissible the pathogen
, the greater the incentive is to make personal investments for control. The converse is also true: if there is a lowered risk of disease, either through vaccination or because of lowered prevalence, individuals may increase their risk-taking behavior. This effect is analogous to the introduction of safety regulations, such as seatbelts in cars, which because they reduce the cost of an accident in terms of expected injury and death, could lead people to drive with less caution and the resulting injuries to nonoccupants and increased nonfatal crashes may offset some of the gains from the use of seatbelts .
Prevalence-dependent behavior introduces a crucial difference with respect to the way individuals respond when the prevalence of a disease increases. If behavior is exogenous or if behavioral responses are assumed to be inelastic with respect to disease prevalence
, the per capita risk of infection in the susceptible population increases as prevalence increases. In contrast, when behavior is endogenous and elastic, hosts can act to reduce their risks. If their responses are strong enough, they can reduce the average per capita risk and offset the increases in the risk of transmission associated with higher prevalence . Alternatively, the waning of perceived risk, either through the diminution of prevalence or the introduction of a vaccine, may lead to increases in risky behavior. For example, models suggested that the introduction of highly active antiretroviral therapy (HAART)
, which significantly reduced the morbidity and mortality associated with HIV
/AIDS, may lead to increases in the incidence of HIV as the perceived risk of HIV/AIDS decreased . Recent analysis suggests that an individual’s likelihood of engaging in unprotected sex is related to their personal analysis of risk, with those who believed that receiving HAART or having an undetectable viral load
protects against transmitting HIV or who had reduced concerns about engaging in unsafe sex given the availability of HAART were more likely to engage in unprotected sex regardless of HIV status .
This behavioral response can have important implications for the timing of public interventions, because prevalence and public subsidies may compete to induce protective behavior . In other words, if prevalence induces the same sort of protective behavior as public subsidies, the subsidies become irrelevant because people will choose to protect themselves when prevalence is high, regardless of the subsidy, and subsidies may not be helpful at the times when they are typically applied.
Although STDs
are logical targets for examining the role of human behavior
in a modeling framework, personal actions are important for other infectious diseases as well. The rapidity with which individuals reduce their contact rate with others during an outbreak of a highly transmissible disease can significantly affect the spread of the disease . Even small reductions in the contact rate can be important, especially for diseases like influenza
or severe acute respiratory syndrome (SARS)
. However, this may also have an impact on policy planning for a biological attack with a disease such as smallpox
.
Individual behavioral responses to interventions for non-sexually transmitted diseases are also important. For example, mass spraying to reduce malaria
transmission can reduce the irritating effects of biting by nuisance mosquitoes and so lead to reduced personal use of bednets . Economic epidemiology strives to incorporate these types of behavior responses into epidemiological models to enhance a model’s utility in evaluating control measures.
between the private gains of individuals and the collective gains of a society, and prevalence-dependent behavior may have significant impacts on vaccine
policy formation. For instance, it was found in an analysis of the hypothetical introduction of a vaccine that would reduce (though not eliminate) the risk of contracting HIV, that individual levels of risk behavior were a significant barrier to eliminating HIV, as small changes in behavior could actually increase the incidence/prevalence of HIV, even if the vaccine were highly efficacious . These results, as well as others , may have contributed to a decision not to release existing semi-efficacious vaccines .
An individual's self-interest and choice often leads to a vaccination uptake rate less than the social optimum as individuals do not take into account the benefit to others. In addition, prevalence dependent behavior suggests how the introduction of a vaccine may affect the spread of a disease. As the prevalence of a disease increases, people will demand to be vaccinated. As prevalence decreases, however, the incentive, and thus demand, will slacken and allow the susceptible population to increase until the disease can reinvade. As long as a vaccine is not free, either monetarily or through true or even perceived side effect
s , demand will be insufficient to pay for the vaccine at some point, leaving some people unvaccinated. If the disease is contagious, it could then begin spreading again among non-vaccinated individuals. Thus, it is impossible to eradicate a vaccine-preventable disease through voluntary vaccination if people act in their own self-interest .
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
and economics
Economics
Economics is the social science that analyzes the production, distribution, and consumption of goods and services. The term economics comes from the Ancient Greek from + , hence "rules of the house"...
. Its premise is to incorporate incentives for healthy behavior and their attendant behavioral responses into an epidemiological context to better understand how diseases are transmitted. This framework should help improve policy responses to epidemic
Epidemic
In epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...
diseases by giving policymakers and health-care providers clear tools for thinking about how certain actions can influence the spread of disease transmission. The main context through which this field emerged was the idea of prevalence-dependence, or disinhibition
Disinhibition
Disinhibition is a term in psychology used to describe a lack of restraint manifested in several ways, including disregard for social conventions, impulsivity, and poor risk assessment. Disinhibition affects motor, instinctual, emotional, cognitive and perceptual aspects with signs and symptoms...
, which suggests that individuals change their behavior as the prevalence of a disease changes. However, economic epidemiology also encompasses other ideas, including the role of externalities, global disease commons and how individuals’ incentives can influence the outcome and cost of health interventions. Strategic epidemiology is a branch of economic epidemiology that adopts an explicitly game theoretic
Game theory
Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...
approach to analyzing the interplay between individual behavior and population wide disease dynamics.
Prevalence-dependence
The spread of an infectious diseaseInfectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
is a population-level phenomenon, but decisions to prevent or treat a disease are typically made by individuals who may change their behavior over the course of an epidemic, especially if their perception of risk
Risk perception
Risk perception is the subjective judgment that people make about the characteristics and severity of a risk. The phrase is most commonly used in reference to natural hazards and threats to the environment or health, such as nuclear power. Several theories have been proposed to explain why...
changes depending on the available information on the epidemics – their decisions will then have population-level consequences. For example, an individual may choose to have unsafe sex
Safe sex
Safe sex is sexual activity engaged in by people who have taken precautions to protect themselves against sexually transmitted diseases such as AIDS. It is also referred to as safer sex or protected sex, while unsafe or unprotected sex is sexual activity engaged in without precautions...
or a doctor may prescribe antibiotics to someone without a confirmed bacterial infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
. In both cases, the choice may be rational from the individual’s point of view but undesirable from a societal perspective.
Limiting the spread of a disease at the population level requires changing individual behavior, which in turn depends on what information individuals have about the level of risk. When risk is low, people will tend to ignore it. However, if the risk of infection is higher, individuals are more likely to take preventive action. Moreover, the more transmissible the pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
, the greater the incentive is to make personal investments for control. The converse is also true: if there is a lowered risk of disease, either through vaccination or because of lowered prevalence, individuals may increase their risk-taking behavior. This effect is analogous to the introduction of safety regulations, such as seatbelts in cars, which because they reduce the cost of an accident in terms of expected injury and death, could lead people to drive with less caution and the resulting injuries to nonoccupants and increased nonfatal crashes may offset some of the gains from the use of seatbelts .
Prevalence-dependent behavior introduces a crucial difference with respect to the way individuals respond when the prevalence of a disease increases. If behavior is exogenous or if behavioral responses are assumed to be inelastic with respect to disease prevalence
Prevalence
In epidemiology, the prevalence of a health-related state in a statistical population is defined as the total number of cases of the risk factor in the population at a given time, or the total number of cases in the population, divided by the number of individuals in the population...
, the per capita risk of infection in the susceptible population increases as prevalence increases. In contrast, when behavior is endogenous and elastic, hosts can act to reduce their risks. If their responses are strong enough, they can reduce the average per capita risk and offset the increases in the risk of transmission associated with higher prevalence . Alternatively, the waning of perceived risk, either through the diminution of prevalence or the introduction of a vaccine, may lead to increases in risky behavior. For example, models suggested that the introduction of highly active antiretroviral therapy (HAART)
Antiretroviral drug
Antiretroviral drugs are medications for the treatment of infection by retroviruses, primarily HIV. When several such drugs, typically three or four, are taken in combination, the approach is known as Highly Active Antiretroviral Therapy, or HAART...
, which significantly reduced the morbidity and mortality associated with HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
/AIDS, may lead to increases in the incidence of HIV as the perceived risk of HIV/AIDS decreased . Recent analysis suggests that an individual’s likelihood of engaging in unprotected sex is related to their personal analysis of risk, with those who believed that receiving HAART or having an undetectable viral load
Viral load
Viral load is a measure of the severity of a viral infection, and can be calculated by estimating the amount of virus in an involved body fluid. For example, it can be given in RNA copies per milliliter of blood plasma...
protects against transmitting HIV or who had reduced concerns about engaging in unsafe sex given the availability of HAART were more likely to engage in unprotected sex regardless of HIV status .
This behavioral response can have important implications for the timing of public interventions, because prevalence and public subsidies may compete to induce protective behavior . In other words, if prevalence induces the same sort of protective behavior as public subsidies, the subsidies become irrelevant because people will choose to protect themselves when prevalence is high, regardless of the subsidy, and subsidies may not be helpful at the times when they are typically applied.
Although STDs
Sexually transmitted disease
Sexually transmitted disease , also known as a sexually transmitted infection or venereal disease , is an illness that has a significant probability of transmission between humans by means of human sexual behavior, including vaginal intercourse, oral sex, and anal sex...
are logical targets for examining the role of human behavior
Human behavior
Human behavior refers to the range of behaviors exhibited by humans and which are influenced by culture, attitudes, emotions, values, ethics, authority, rapport, hypnosis, persuasion, coercion and/or genetics....
in a modeling framework, personal actions are important for other infectious diseases as well. The rapidity with which individuals reduce their contact rate with others during an outbreak of a highly transmissible disease can significantly affect the spread of the disease . Even small reductions in the contact rate can be important, especially for diseases like influenza
Influenza
Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
or severe acute respiratory syndrome (SARS)
Severe acute respiratory syndrome
Severe Acute Respiratory Syndrome is a respiratory disease in humans which is caused by the SARS coronavirus . Between November 2002 and July 2003 an outbreak of SARS in Hong Kong nearly became a pandemic, with 8,422 cases and 916 deaths worldwide according to the WHO...
. However, this may also have an impact on policy planning for a biological attack with a disease such as smallpox
Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...
.
Individual behavioral responses to interventions for non-sexually transmitted diseases are also important. For example, mass spraying to reduce malaria
Malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
transmission can reduce the irritating effects of biting by nuisance mosquitoes and so lead to reduced personal use of bednets . Economic epidemiology strives to incorporate these types of behavior responses into epidemiological models to enhance a model’s utility in evaluating control measures.
Vaccination
Immunization represents a classic case of a social dilemma: a conflict of interestConflict of interest
A conflict of interest occurs when an individual or organization is involved in multiple interests, one of which could possibly corrupt the motivation for an act in the other....
between the private gains of individuals and the collective gains of a society, and prevalence-dependent behavior may have significant impacts on vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
policy formation. For instance, it was found in an analysis of the hypothetical introduction of a vaccine that would reduce (though not eliminate) the risk of contracting HIV, that individual levels of risk behavior were a significant barrier to eliminating HIV, as small changes in behavior could actually increase the incidence/prevalence of HIV, even if the vaccine were highly efficacious . These results, as well as others , may have contributed to a decision not to release existing semi-efficacious vaccines .
An individual's self-interest and choice often leads to a vaccination uptake rate less than the social optimum as individuals do not take into account the benefit to others. In addition, prevalence dependent behavior suggests how the introduction of a vaccine may affect the spread of a disease. As the prevalence of a disease increases, people will demand to be vaccinated. As prevalence decreases, however, the incentive, and thus demand, will slacken and allow the susceptible population to increase until the disease can reinvade. As long as a vaccine is not free, either monetarily or through true or even perceived side effect
Side effect
In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequences of the use of a drug.Occasionally, drugs are...
s , demand will be insufficient to pay for the vaccine at some point, leaving some people unvaccinated. If the disease is contagious, it could then begin spreading again among non-vaccinated individuals. Thus, it is impossible to eradicate a vaccine-preventable disease through voluntary vaccination if people act in their own self-interest .