Public health has been described as "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals."[51] It is concerned with threats to the overall health of a community based on population health analysis. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic). Public health has many sub-fields, but typically includes the interdisciplinary categories of epidemiology, biostatistics and health services. Environmental health, community health, behavioral health, and occupational health are also important areas of public health.
Health science is the branch of science focused on health. There are two main approaches to health science: the study and research of the body and health-related issues to understand how humans (and animals) function, and the application of that knowledge to improve health and to prevent and cure diseases and other physical and mental impairments. The science builds on many sub-fields, including biology, biochemistry, physics, epidemiology, pharmacology, medical sociology. Applied health sciences endeavor to better understand and improve human health through applications in areas such as health education, biomedical engineering, biotechnology and public health.
The private health system in Australia operates on a "community rating" basis, whereby premiums do not vary solely because of a person's previous medical history, current state of health, or (generally speaking) their age (but see Lifetime Health Cover below). Balancing this are waiting periods, in particular for pre-existing conditions (usually referred to within the industry as PEA, which stands for "pre-existing ailment"). Funds are entitled to impose a waiting period of up to 12 months on benefits for any medical condition the signs and symptoms of which existed during the six months ending on the day the person first took out insurance. They are also entitled to impose a 12-month waiting period for benefits for treatment relating to an obstetric condition, and a 2-month waiting period for all other benefits when a person first takes out private insurance. Funds have the discretion to reduce or remove such waiting periods in individual cases. They are also free not to impose them to begin with, but this would place such a fund at risk of "adverse selection", attracting a disproportionate number of members from other funds, or from the pool of intending members who might otherwise have joined other funds. It would also attract people with existing medical conditions, who might not otherwise have taken out insurance at all because of the denial of benefits for 12 months due to the PEA Rule. The benefits paid out for these conditions would create pressure on premiums for all the fund's members, causing some to drop their membership, which would lead to further rises in premiums, and a vicious cycle of higher premiums-leaving members would ensue.
Before the development of medical expense insurance, patients were expected to pay health care costs out of their own pockets, under what is known as the fee-for-service business model. During the middle-to-late 20th century, traditional disability insurance evolved into modern health insurance programs. One major obstacle to this development was that early forms of comprehensive health insurance were enjoined by courts for violating the traditional ban on corporate practice of the professions by for-profit corporations.[64] State legislatures had to intervene and expressly legalize health insurance as an exception to that traditional rule. Today, most comprehensive private health insurance programs cover the cost of routine, preventive, and emergency health care procedures, and most prescription drugs (but this is not always the case).
As per the Constitution of Canada, health care is mainly a provincial government responsibility in Canada (the main exceptions being federal government responsibility for services provided to aboriginal peoples covered by treaties, the Royal Canadian Mounted Police, the armed forces, and Members of Parliament). Consequently, each province administers its own health insurance program. The federal government influences health insurance by virtue of its fiscal powers – it transfers cash and tax points to the provinces to help cover the costs of the universal health insurance programs. Under the Canada Health Act, the federal government mandates and enforces the requirement that all people have free access to what are termed "medically necessary services," defined primarily as care delivered by physicians or in hospitals, and the nursing component of long-term residential care. If provinces allow doctors or institutions to charge patients for medically necessary services, the federal government reduces its payments to the provinces by the amount of the prohibited charges. Collectively, the public provincial health insurance systems in Canada are frequently referred to as Medicare.[15] This public insurance is tax-funded out of general government revenues, although British Columbia and Ontario levy a mandatory premium with flat rates for individuals and families to generate additional revenues - in essence, a surtax. Private health insurance is allowed, but in six provincial governments only for services that the public health plans do not cover (for example, semi-private or private rooms in hospitals and prescription drug plans). Four provinces allow insurance for services also mandated by the Canada Health Act, but in practice there is no market for it. All Canadians are free to use private insurance for elective medical services such as laser vision correction surgery, cosmetic surgery, and other non-basic medical procedures. Some 65% of Canadians have some form of supplementary private health insurance; many of them receive it through their employers.[16] Private-sector services not paid for by the government account for nearly 30 percent of total health care spending.[17]

Note 2 This material is for informational purposes only and should not be considered advice, a solicitation, a recommendation, or an offer to buy any specific plan or product. This should not be used as the primary basis for making your decision. USAA encourages you to consider your needs when selecting products and does not make specific product recommendations for individuals. None of the foregoing is a substitute for professional medical advice, examination, diagnosis, or treatment.
Public health also takes various actions to limit the health disparities between different areas of the country and, in some cases, the continent or world. One issue is the access of individuals and communities to health care in terms of financial, geographical or socio-cultural constraints to accessing and using services.[53] Applications of the public health system include the areas of maternal and child health, health services administration, emergency response, and prevention and control of infectious and chronic diseases.
Just as there was a shift from viewing disease as a state to thinking of it as a process, the same shift happened in definitions of health. Again, the WHO played a leading role when it fostered the development of the health promotion movement in the 1980s. This brought in a new conception of health, not as a state, but in dynamic terms of resiliency, in other words, as "a resource for living". 1984 WHO revised the definition of health defined it as "the extent to which an individual or group is able to realize aspirations and satisfy needs and to change or cope with the environment. Health is a resource for everyday life, not the objective of living; it is a positive concept, emphasizing social and personal resources, as well as physical capacities".[10] Thus, health referred to the ability to maintain homeostasis and recover from insults. Mental, intellectual, emotional and social health referred to a person's ability to handle stress, to acquire skills, to maintain relationships, all of which form resources for resiliency and independent living.[9] This opens up many possibilities for health to be taught, strengthened and learned.