In statistics, epidemiology, marketing and demography, a cohort is a group of subjects who share a defining characteristic (typically subjects who experienced a common event in a selected time period, such as birth or graduation).
In statistics, epidemiology, marketing and demography, a cohort is a group of subjects who share a defining characteristic (typically subjects who experienced a common event in a selected time period, such as birth or graduation).
Cohort data can oftentimes be more advantageous to demographers than period data. Because cohort data is honed to a specific time period, it is usually more accurate. It is more accurate because it can be tuned to retrieve custom data for a specific study.[ citation needed ]
In addition, cohort data is not affected by tempo effects, unlike period data. However, cohort data can be disadvantageous in the sense that it can take a long amount of time to collect the data necessary for the cohort study. [1] Another disadvantage of cohort studies is that it can be extremely costly to carry out, since the study will go on for a long period of time, demographers often require sufficient funds to fuel the study.[ citation needed ]
Demography often contrasts cohort perspectives and period perspectives. For instance, the total cohort fertility rate is an index of the average completed family size for cohorts of women, but since it can only be known for women who have finished child-bearing, it cannot be measured for currently fertile women. It can be calculated as the sum of the cohort's age-specific fertility rates that obtain as it ages through time. In contrast, the total period fertility rate uses current age-specific fertility rates to calculate the completed family size for a notional woman, were she to experience these fertility rates through her life.[ citation needed ]
A study on a cohort is a cohort study.
Two important types of cohort studies are:
Demography is the statistical study of human populations: their size, composition, and how they change through the interplay of fertility (births), mortality (deaths), and migration.
Epidemiology is the study and analysis of the distribution, patterns and determinants of health and disease conditions in a defined population.
In demography, demographic transition is a phenomenon and theory which refers to the historical shift from high birth rates and high death rates to low birth rates and low death rates, as societies attain more technology, education and economic development. The demographic transition has occurred in most of the world over the past two centuries, bringing the unprecedented population growth of the post-Malthusian period, then reducing birth rates and population growth significantly in all regions of the world. The demographic transition strengthens economic growth process by three changes: (i) reduced dilution of capital and land stock, (ii) increased investment in human capital, and (iii) increased size of the labor force relative to the total population and changed age population distribution. Although this shift has occurred in many industrialized countries, the theory and model are frequently imprecise when applied to individual countries due to specific social, political and economic factors affecting particular populations.
Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate is the average number of children born during an individual's lifetime. In medicine, fertility refers to the ability to have children, and infertility refers to difficulty in reproducing naturally. In general, infertility or subfertility in humans is defined as not being able to conceive a child after one year of unprotected sex. The antithesis of fertility is infertility, while the antithesis of fecundity is sterility.
Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population intended to be analyzed. It is sometimes referred to as the selection effect. The phrase "selection bias" most often refers to the distortion of a statistical analysis, resulting from the method of collecting samples. If the selection bias is not taken into account, then some conclusions of the study may be false.
A cohort study is a particular form of longitudinal study that samples a cohort, performing a cross-section at intervals through time. It is a type of panel study where the individuals in the panel share a common characteristic.
A case–control study is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case–control studies are often used to identify factors that may contribute to a medical condition by comparing subjects who have the condition with patients who do not have the condition but are otherwise similar. They require fewer resources but provide less evidence for causal inference than a randomized controlled trial. A case–control study is often used to produce an odds ratio. Some statistical methods make it possible to use a case–control study to also estimate relative risk, risk differences, and other quantities.
Clinical study design is the formulation of trials and experiments, as well as observational studies in medical, clinical and other types of research involving human beings. The goal of a clinical study is to assess the safety, efficacy, and / or the mechanism of action of an investigational medicinal product (IMP) or procedure, or new drug or device that is in development, but potentially not yet approved by a health authority. It can also be to investigate a drug, device or procedure that has already been approved but is still in need of further investigation, typically with respect to long-term effects or cost-effectiveness.
A nested case–control (NCC) study is a variation of a case–control study in which cases and controls are drawn from the population in a fully enumerated cohort.
Natural fertility is the fertility that exists without birth control or other medical interventions. The control is the number of children birthed to the parents and is modified as the number of children reaches the maximum. Natural fertility tends to decrease as a society modernizes. Women in a pre-modernized society typically have given birth to a large number of children by the time they are 50 years old, while women in post-modernized society only bear a small number by the same age. However, during modernization natural fertility rises, before family planning is practiced.
Social cognitive theory (SCT), used in psychology, education, and communication, holds that portions of an individual's knowledge acquisition can be directly related to observing others within the context of social interactions, experiences, and outside media influences. This theory was advanced by Albert Bandura as an extension of his social learning theory. The theory states that when people observe a model performing a behavior and the consequences of that behavior, they remember the sequence of events and use this information to guide subsequent behaviors. Observing a model can also prompt the viewer to engage in behavior they already learned. Depending on whether people are rewarded or punished for their behavior and the outcome of the behavior, the observer may choose to replicate behavior modeled. Media provides models for a vast array of people in many different environmental settings.
The middle of the 20th century was marked by a significant and persistent increase in fertility rates in many countries of the world, especially in the Western world. The term baby boom is often used to refer to this particular boom, generally considered to have started immediately after World War II, although some demographers place it earlier or during the war. This terminology led to those born during this baby boom being nicknamed the baby boomer generation.
Historical demography is the quantitative study of human population in the past. It is concerned with population size, with the three basic components of population change, and with population characteristics related to those components, such as marriage, socioeconomic status, and the configuration of families.
A case series is a type of medical research study that tracks subjects with a known exposure, such as patients who have received a similar treatment, or examines their medical records for exposure and outcome. Case series may be consecutive or non-consecutive, depending on whether all cases presenting to the reporting authors over a period were included, or only a selection. When information on more than three patients is included, the case series is considered to be a systematic investigation designed to contribute to generalizable knowledge, and therefore submission is required to an institutional review board (IRB). Case series usually contain demographic information about the patient(s), for example, age, gender, ethnic origin. etc.
A retrospective cohort study, also called a historic cohort study, is a longitudinal cohort study used in medical and psychological research. A cohort of individuals that share a common exposure factor is compared with another group of equivalent individuals not exposed to that factor, to determine the factor's influence on the incidence of a condition such as disease or death. Retrospective cohort studies have existed for approximately as long as prospective cohort studies.
A prospective cohort study is a longitudinal cohort study that follows over time a group of similar individuals (cohorts) who differ with respect to certain factors under study to determine how these factors affect rates of a certain outcome. For example, one might follow a cohort of middle-aged truck drivers who vary in terms of smoking habits to test the hypothesis that the 20-year incidence rate of lung cancer will be highest among heavy smokers, followed by moderate smokers, and then non–smokers.
Fertility factors are determinants of the number of children that an individual is likely to have. Fertility factors are mostly positive or negative correlations without certain causations.
Henri Leridon was born on 15 July 1942 in Algiers, where his father was an officer. He is a French demographer and director of research emeritus at the Institut national d'études démographiques (Ined).
The effects of early-life exposures to anesthesia on the brain in humans are controversial. Evidence from nonhuman primate research suggests significant developmental neurotoxicity and long-term social impairment, with a dose–response relationship where repeated exposures cause a more severe impact than single ones. Research in humans has not found conclusive clinical evidence of cognitive impairment; however, systematic reviews imply the possibility of greater behavioural impairments in children exposed to anesthesia before the age of three than control subjects.