Risk factor
Encyclopedia
In epidemiology
, a risk factor is a variable associated with an increased risk
of disease
or infection
. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.
al and not necessarily causal
, because correlation does not prove causation. For example, being young cannot be said to cause measles
, but young people have a higher rate of measles because they are less likely to have developed immunity
during a previous epidemic. Statistical
methods are frequently used to assess the strength of an association and to provide causal evidence (for example in the study
of the link between smoking and lung cancer
). Statistical analysis along with the biological sciences can establish that risk factors are causal. Some prefer the term risk factor to mean causal determinants of increased rates of disease, and for unproven links to be called possible risks, associations, etc.
it confers, which is evaluated by comparing the risk of those exposed to the potential risk factor to those not exposed. Let's say that at a wedding, 74 people ate the chicken and 22 of them were ill, while of the 35 people who had the fish or vegetarian meal only 2 were ill. Did the chicken make the people ill?
So the chicken
eaters' risk = 22/74 = 0.297
And non-chicken eaters' risk = 2/35 = 0.057.
Those who ate the chicken had a risk over five times as high as those who did not, that is, a relative risk of more than five. This suggests that eating chicken was the cause of the illness, but this is not proof.
factors, and need to be controlled for, e.g. by stratification. The potentially confounding determinants varies with what outcome is studied, but the following general risk factors are common to most epidemiological associations, and are the determinants most commonly controlled for in epidemiological studies:
Other less commonly adjusted for possible confounders include:
Director Dr. William B. Kannel a 1961 article in Annals of Internal Medicine.
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...
, a risk factor is a variable associated with an increased risk
Risk
Risk is the potential that a chosen action or activity will lead to a loss . The notion implies that a choice having an influence on the outcome exists . Potential losses themselves may also be called "risks"...
of disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
or 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...
. Sometimes, determinant is also used, being a variable associated with either increased or decreased risk.
Correlation vs causation
Risk factors or determinants are correlationCorrelation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
al and not necessarily causal
Causality
Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....
, because correlation does not prove causation. For example, being young cannot be said to cause measles
Measles
Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
, but young people have a higher rate of measles because they are less likely to have developed immunity
Immunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...
during a previous epidemic. Statistical
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....
methods are frequently used to assess the strength of an association and to provide causal evidence (for example in the study
British Doctors Study
The British Doctors Study is the generally accepted name of a prospective cohort study which ran from 1951 to 2001, and in 1956 provided convincing statistical proof that tobacco smoking increased the risk of lung cancer.-Context:...
of the link between smoking and lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...
). Statistical analysis along with the biological sciences can establish that risk factors are causal. Some prefer the term risk factor to mean causal determinants of increased rates of disease, and for unproven links to be called possible risks, associations, etc.
Terms of description
Mainly taken from risk factors for breast cancer, risk factors can be described in terms of, for example:- Relative riskRelative riskIn statistics and mathematical epidemiology, relative risk is the risk of an event relative to exposure. Relative risk is a ratio of the probability of the event occurring in the exposed group versus a non-exposed group....
, such as "A woman is more than 100 times more likely to develop breast cancer in her 60s than in her 20s." - Fraction of incidences occurring in the group having the property of or being exposed to the risk factor, such as "99% of breast cancer cases are diagnosed in women"
- Increase in incidence in the exposed group, such as "each daily alcoholic beverage increases the incidence of breast cancer by 11 cases per 1000 women"
- Hazard ratioHazard ratioIn survival analysis, the hazard ratio is the ratio of the hazard rates corresponding to the conditions described by two sets of explanatory variables. For example, in a drug study, the treated population may die at twice the rate per unit time as the control population. The hazard ratio would be...
, such as "an increase in both total and invasive breast cancers in women randomized to receive estrogen and progestin for an average of 5 years, with a hazard ratio of 1.24 compared to controls"
Example
The following example of a risk factor is described in terms of the relative riskRelative risk
In statistics and mathematical epidemiology, relative risk is the risk of an event relative to exposure. Relative risk is a ratio of the probability of the event occurring in the exposed group versus a non-exposed group....
it confers, which is evaluated by comparing the risk of those exposed to the potential risk factor to those not exposed. Let's say that at a wedding, 74 people ate the chicken and 22 of them were ill, while of the 35 people who had the fish or vegetarian meal only 2 were ill. Did the chicken make the people ill?
So the chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...
eaters' risk = 22/74 = 0.297
And non-chicken eaters' risk = 2/35 = 0.057.
Those who ate the chicken had a risk over five times as high as those who did not, that is, a relative risk of more than five. This suggests that eating chicken was the cause of the illness, but this is not proof.
General determinants
The probability of an outcome usually depends on an interplay between multiple risk factors. When performing epidemiological studies to evaluate one or more determinants for a specific outcome, the other determinants may act as confoundingConfounding
In statistics, a confounding variable is an extraneous variable in a statistical model that correlates with both the dependent variable and the independent variable...
factors, and need to be controlled for, e.g. by stratification. The potentially confounding determinants varies with what outcome is studied, but the following general risk factors are common to most epidemiological associations, and are the determinants most commonly controlled for in epidemiological studies:
- Age
- Sex or gender
- Ethnicity
Other less commonly adjusted for possible confounders include:
- Social status/income
- Geographic location
- Genetic predisposition
- Gender identity
- Occupation
- Sexual orientation
- Level of chronic stressChronic stressChronic stress is the response to emotional pressure suffered for a prolonged period over which an individual perceives he or she has no control. It involves an endocrine system response in which occurs a release of corticosteroids...
- Diet
- Level of physical exercisePhysical exercisePhysical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons including strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance, as well as for the purpose of...
- Alcohol consumption and tobacco smokingTobacco smokingTobacco smoking is the practice where tobacco is burned and the resulting smoke is inhaled. The practice may have begun as early as 5000–3000 BCE. Tobacco was introduced to Eurasia in the late 16th century where it followed common trade routes...
- Other social determinants of healthSocial determinants of healthSocial determinants of health are the economic and social conditions under which people live which determine their health. They are "societal risk conditions", rather than individual risk factors that either increase or decrease the risk for a disease, for example for cardiovascular disease and...
Risk marker
A risk marker is a variable that is quantitatively associated with a disease or other outcome, but direct alteration of the risk marker does not necessarily alter the risk of the outcome.History
The term "risk factor" was first coined by former Framingham Heart StudyFramingham Heart Study
The Framingham Heart Study is a long-term, ongoing cardiovascular study on residents of the town of Framingham, Massachusetts. The study began in 1948 with 5,209 adult subjects from Framingham, and is now on its third generation of participants...
Director Dr. William B. Kannel a 1961 article in Annals of Internal Medicine.
Further reading
- Case, S.P. and Haines, K.R. (2009) Understanding Youth Offending: Risk Factor Research, Policy and Practice. Cullompton: Willan. http://www.willanpublishing.co.uk/cgi-bin/indexer?product=9781843923411