Misplaced Pages

#820179

43-452: Prevalence is the number of disease cases present in a particular population at a given time, whereas incidence is the number of new cases that develop during a specified time period. Prevalence answers "How many people have this disease right now?" or "How many people have had this disease during this time period?". Incidence answers "How many people acquired the disease [during a specified time period]?". However, mathematically, prevalence

86-576: A   d i s e a s e t h e   t o t a l   t i m e   a t   r i s k   f o r   a l l   p e o p l e   t o   g e t   t h e   d i s e a s e {\displaystyle Incidence\ rate={\frac {the\ number\ of\ subjects\ developing\ a\ disease}{the\ total\ time\ at\ risk\ for\ all\ people\ to\ get\ the\ disease}}} One of

129-405: A s e   o v e r   a   c e r t a i n   p e r i o d t h e   t o t a l   n u m b e r   o f   s u b j e c t s   f o l l o w e d   o v e r   t h

172-410: A t   p e r i o d {\displaystyle Incidence={\frac {number\ of\ subjects\ developing\ the\ disease\ over\ a\ certain\ period}{the\ total\ number\ of\ subjects\ followed\ over\ that\ period}}} For example, if a population contains 1,000 persons and 28 develop a condition from the time the disease first occurred until two years later, the cumulative incidence

215-412: A proportion (typically expressed as a percentage ). For example, the prevalence of obesity among American adults in 2001 was estimated by the U. S. Centers for Disease Control (CDC) at approximately 20.9%. Prevalence is a term that means being widespread and it is distinct from incidence . Prevalence is a measurement of all individuals affected by the disease at a particular time, whereas incidence

258-436: A " psychosis ", and described "the three major psychoses" as schizophrenia, epilepsy, and manic-depressive illness . In the field of medical genetics, the term "syndrome" is traditionally only used when the underlying genetic cause is known. Thus, trisomy 21 is commonly known as Down syndrome. Until 2005, CHARGE syndrome was most frequently referred to as "CHARGE association". When the major causative gene ( CHD7 ) for

301-483: A 10-year period: If you were to measure prevalence you would simply take the total number of cases (25 + 20 + 30 = 75) and divide by your sample population (225). So prevalence would be 75/225 = 0.33 or 33% (by the end of the study). This tells you how widespread HIV is in your sample population, but little about the actual risk of developing HIV for any person over a coming year. To measure incidence rate you must take into account how many years each person contributed to

344-411: A circumstance a limited positive predictive value , PPV, yields high false positive rates even in presence of a specificity which is very close to 100%. Incidence (epidemiology) In epidemiology , incidence reflects the number of new cases of a given medical condition in a population within a specified period of time. Incidence proportion ( IP ), also known as cumulative incidence ,

387-440: A given disease at any point in their lifetime." Period prevalence is the proportion of the population with a given disease or condition over a specific period of time. It could describe how many people in a population had a cold over the cold season in 2006, for example. It is expressed as a percentage of the population and can be described by the following formula: Period prevalence (proportion) = Number of cases that existed in

430-420: A given period ÷ Number of people in the population during this period The relationship between incidence (rate), point prevalence (ratio) and period prevalence (ratio) is easily explained via an analogy with photography. Point prevalence is akin to a flashlit photograph: what is happening at this instant frozen in time. Period prevalence is analogous to a long exposure (seconds, rather than an instant) photograph:

473-529: A history of a disorder at interview are false positives for such a medical condition and apparently never developed a fully clinical syndrome . A different but related problem in evaluating the public health significance of psychiatric conditions has been highlighted by Robert Spitzer of Columbia University : fulfillment of diagnostic criteria and the resulting diagnosis do not necessarily imply need for treatment. A well-known statistical problem arises when ascertaining rates for disorders and conditions with

SECTION 10

#1732848478821

516-500: A low incidence yet will continue to have a high prevalence (because it takes a long time to cure, so the fraction of individuals that are affected remains high). In contrast, a disease that has a short duration may have a low prevalence and a high incidence. When the incidence is approximately constant for the duration of the disease, prevalence is approximately the product of disease incidence and average disease duration, so prevalence = incidence × duration . The importance of this equation

559-436: A number of symptoms suggesting a particular disease or condition but does not meet the defined criteria used to make a diagnosis of that disease or condition. This can be a bit subjective because it is ultimately up to the clinician to make the diagnosis. This could be because it has not advanced to the level or passed a threshold or just similar symptoms cause by other issues. Subclinical is synonymous since one of its definitions

602-446: A particular time, such as a particular date. It is like a snapshot of the disease in time. It can be used for statistics on the occurrence of chronic diseases . This is in contrast to period prevalence which is a measure of the proportion of people in a population who have a disease or condition over a specific period of time, say a season, or a year. Point prevalence can be described by the formula: Prevalence = Number of existing cases on

645-486: A relatively low population prevalence or base rate . Even assuming that lay interview diagnoses are highly accurate in terms of sensitivity and specificity and their corresponding area under the ROC curve (that is, AUC , or area under the receiver operating characteristic curve), a condition with a relatively low prevalence or base-rate is bound to yield high false positive rates, which exceed false negative rates; in such

688-840: A single identifiable pathogenesis. Examples of infectious syndromes include encephalitis and hepatitis , which can both have several different infectious causes. The more specific definition employed in medical genetics describes a subset of all medical syndromes. Early texts by physicians noted the symptoms of various maladies and introduced diagnoses based upon those symptoms. For example, Avicenna 's The Canon of Medicine (1025) describes diagnosing pleurisy by its symptoms, including chronic fever, cough, shooting pains, and labored breathing. The 17th century doctor Thomas Sydenham likewise approached diagnoses based upon collections of symptoms. Psychiatric syndromes often called psychopathological syndromes ( psychopathology refers both to psychic dysfunctions occurring in mental disorders , and

731-422: A specific date ÷ Number of people in the population on this date It can be said that a very small error applied over a very large number of individuals (that is, those who are not affected by the condition in the general population during their lifetime; for example, over 95%) produces a relevant, non-negligible number of subjects who are incorrectly classified as having the condition or any other condition which

774-402: Is "where some criteria are met but not enough to achieve clinical status"; but subclinical is not always interchangeable since it can also mean "not detectable or producing effects that are not detectable by the usual clinical tests"; i.e., asymptomatic. In medicine, a broad definition of syndrome is used, which describes a collection of symptoms and findings without necessarily tying them to

817-475: Is 28 cases per 1,000 persons, i.e. 2.8%. The incidence rate can be calculated by dividing the number of subjects developing a disease by the total time at risk from all patients: I n c i d e n c e   r a t e = t h e   n u m b e r   o f   s u b j e c t s   d e v e l o p i n g  

860-418: Is a measurement of the number of new individuals who contract a disease during a particular period of time. Prevalence is a useful parameter when talking about long-lasting diseases, such as HIV , but incidence is more useful when talking about diseases of short duration, such as chickenpox . Lifetime prevalence (LTP) is the proportion of individuals in a population that at some point in their life (up to

903-450: Is a much more accurate measure of risk than prevalence. Syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek σύνδρομον, meaning "concurrence". When a syndrome is paired with a definite cause this becomes a disease. In some instances, a syndrome

SECTION 20

#1732848478821

946-416: Is defined as the probability that a particular event, such as occurrence of a particular disease, has occurred in a specified period: I n c i d e n c e = n u m b e r   o f   s u b j e c t s   d e v e l o p i n g   t h e   d i s e

989-420: Is in the relation between prevalence and incidence; for example, when the incidence increases, then the prevalence must also increase. Note that this relation does not hold for age-specific prevalence and incidence, where the relation becomes more complicated. Consider the following example. Say you are looking at a sample population of 225 people, and want to determine the incidence rate of developing HIV over

1032-402: Is not a disease but simply a set of symptoms. If an underlying genetic cause is suspected but not known, a condition may be referred to as a genetic association (often just "association" in context). By definition, an association indicates that the collection of signs and symptoms occurs in combination more frequently than would be likely by chance alone . Syndromes are often named after

1075-467: Is proportional to the product of the incidence and the average duration of the disease. In particular, when the prevalence is low (<10%), the relationship can be expressed as: Caution must be practiced as this relationship is only applicable when the following two conditions are met: 1) prevalence is low and 2) the duration is constant (or an average can be taken). A general formulation requires differential equations . In science, prevalence describes

1118-456: Is so closely linked with a pathogenesis or cause that the words syndrome , disease , and disorder end up being used interchangeably for them. This substitution of terminology often confuses the reality and meaning of medical diagnoses. This is especially true of inherited syndromes. About one third of all phenotypes that are listed in OMIM are described as dysmorphic, which usually refers to

1161-428: Is the object of a survey study: these subjects are the so-called false positives; such reasoning applies to the 'false positive' but not the 'false negative' problem where we have an error applied over a relatively very small number of individuals to begin with (that is, those who are affected by the condition in the general population; for example, less than 5%). Hence, a very high percentage of subjects who seem to have

1204-422: Is usually more useful than prevalence in understanding the disease etiology: for example, if the incidence rate of a disease in a population increases, then there is a risk factor that promotes the incidence. For example, consider a disease that takes a long time to cure and was widespread in 2002 but dissipated in 2003. This disease will have both high incidence and high prevalence in 2002, but in 2003 it will have

1247-461: Is usually not a separate discipline from nosology and differential diagnosis generally, which inherently involve pattern recognition (both sentient and automated ) and differentiation among overlapping sets of signs and symptoms. Teratology (dysmorphology) by its nature involves the defining of congenital syndromes that may include birth defects (pathoanatomy), dysmetabolism (pathophysiology), and neurodevelopmental disorders . When there are

1290-489: The condition was discovered, the name was changed. The consensus underlying cause of VACTERL association has not been determined, and thus it is not commonly referred to as a "syndrome". In biology, "syndrome" is used in a more general sense to describe characteristic sets of features in various contexts. Examples include behavioral syndromes , as well as pollination syndromes and seed dispersal syndromes . In orbital mechanics and astronomy, Kessler syndrome refers to

1333-410: The disease, whereas prevalence indicates how widespread the disease is. Prevalence is the proportion of the total number of cases to the total population and is more a measure of the burden of the disease on society with no regard to time at risk or when subjects may have been exposed to a possible risk factor. Prevalence can also be measured with respect to a specific subgroup of a population. Incidence

Prevalence - Misplaced Pages Continue

1376-428: The effect where the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade in which each collision generates space debris that increases the likelihood of further collisions. In quantum error correction theory syndromes correspond to errors in code words which are determined with syndrome measurements, which only collapse the state on an error state, so that

1419-407: The error can be corrected without affecting the quantum information stored in the code words. There is no set common convention for the naming of newly identified syndromes. In the past, syndromes were often named after the physician or scientist who identified and described the condition in an initial publication. These are referred to as "eponymous syndromes". In some cases, diseases are named after

1462-494: The facial gestalt. For example, Down syndrome , Wolf–Hirschhorn syndrome , and Andersen–Tawil syndrome are disorders with known pathogeneses, so each is more than just a set of signs and symptoms, despite the syndrome nomenclature. In other instances, a syndrome is not specific to only one disease. For example, toxic shock syndrome can be caused by various toxins; another medical syndrome named as premotor syndrome can be caused by various brain lesions; and premenstrual syndrome

1505-400: The important advantages of incidence rate is that it doesn't require all subjects to be present for the whole study because it's only interested in the time at risk. Incidence should not be confused with prevalence , which is the proportion of cases in the population at a given time rather than rate of occurrence of new cases. Thus, incidence conveys information about the risk of contracting

1548-465: The mild disorders, consists of five syndromes: emotional, paranoid, hysterical , delirious , and impulsive. The second, intermediate, group includes two syndromes: schizophrenic syndrome and speech-hallucinatory syndrome . The third includes the most severe disorders, and consists of three syndromes: epileptic , oligophrenic and dementia . In Kraepelin's era, epilepsy was viewed as a mental illness; Karl Jaspers also considered "genuine epilepsy"

1591-477: The non-possessive form, while European references often use the possessive. A 2009 study demonstrated a trend away from the possessive form in Europe in medical literature from 1970 through 2008. Even in syndromes with no known etiology , the presence of the associated symptoms with a statistically improbable correlation normally leads the researchers to hypothesize that there exists an unknown underlying cause for all

1634-419: The number of events recorded in the photo whilst the camera shutter was open. In a movie each frame records an instant (point prevalence); by looking from frame to frame one notices new events (incident events) and can relate the number of such events to a period (number of frames); see incidence rate . Point prevalence is a measure of the proportion of people in a population who have a disease or condition at

1677-448: The patient who initially presents with symptoms, or their home town ( Stockholm syndrome ). There have been isolated cases of patients being eager to have their syndromes named after them, while their physicians are hesitant. When a syndrome is named after a person, there is some difference of opinion as to whether it should take the possessive form or not (e.g. Down syndrome vs. Down's syndrome). North American usage has tended to favor

1720-445: The physician or group of physicians that discovered them or initially described the full clinical picture. Such eponymous syndrome names are examples of medical eponyms . Recently, there has been a shift towards naming conditions descriptively (by symptoms or underlying cause) rather than eponymously, but the eponymous syndrome names often persist in common usage. The defining of syndromes has sometimes been termed syndromology, but it

1763-1676: The study of the origin, diagnosis, development, and treatment of mental disorders). In Russia those psychopathological syndromes are used in modern clinical practice and described in psychiatric literature in the details: asthenic syndrome , obsessive syndrome , emotional syndromes (for example, manic syndrome , depressive syndrome), Cotard's syndrome , catatonic syndrome , hebephrenic syndrome, delusional and hallucinatory syndromes (for example, paranoid syndrome, paranoid-hallucinatory syndrome, Kandinsky - Clérambault's syndrome also known as syndrome of psychic automatism, hallucinosis), paraphrenic syndrome , psychopathic syndromes (includes all personality disorders), clouding of consciousness syndromes (for example, twilight clouding of consciousness, amential syndrome also known as amentia, delirious syndrome , stunned consciousness syndrome, oneiroid syndrome ), hysteric syndrome, neurotic syndrome , Korsakoff's syndrome , hypochondriacal syndrome , paranoiac syndrome, senestopathic syndrome, encephalopathic syndrome . Some examples of psychopathological syndromes used in modern Germany are psychoorganic syndrome , depressive syndrome, paranoid-hallucinatory syndrome, obsessive-compulsive syndrome , autonomic syndrome, hostility syndrome, manic syndrome , apathy syndrome . Münchausen syndrome , Ganser syndrome , neuroleptic-induced deficit syndrome , olfactory reference syndrome are also well-known. The most important psychopathological syndromes were classified into three groups ranked in order of severity by German psychiatrist Emil Kraepelin (1856—1926). The first group, which includes

Prevalence - Misplaced Pages Continue

1806-603: The study, and when they developed HIV because when a subject develops HIV he stops being at risk. When it is not known exactly when a person develops the disease in question, epidemiologists frequently use the actuarial method, and assume it was developed at a half-way point between follow-ups. In this calculation: That is a total of (1500 + 275) = 1775 person-years of life. Now take the 50 new cases of HIV, and divide by 1775 to get 0.028, or 28 cases of HIV per 1000 population, per year. In other words, if you were to follow 1000 people for one year, you would see 28 new cases of HIV. This

1849-442: The time of assessment) have experienced a "case", e.g., a disease; a traumatic event; or a behavior, such as committing a crime. Often, a 12-month prevalence (or some other type of "period prevalence") is provided in conjunction with lifetime prevalence. Point prevalence is the prevalence of disorder at a specific point in time (a month or less). Lifetime morbid risk is "the proportion of a population that might become afflicted with

#820179