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Glossary
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Age Adjusted Mortality Rate: a mortality rate statistically modified to eliminate the effect of different age distribution in the different populations.
Age Specific Mortality Rate: a mortality rate limited to a particular age group.
Analytic Epidemiology: the aspect of epidemiology concerned with the search for health-related causes and effects. Uses comparison groups, which provide baseline data, to quantify the association between exposures and outcomes, and test hypotheses about causal relationships.
Applied Epidemiology: the application or practice of epidemiology to address public health issues.
Asthma: is a very common chronic disease involving the respiratory system in which the airways occasionally constrict, become inflamed, and are lined with excessive amounts of mucus. This airway narrowing causes symptoms such as wheezing, shortness of breath, chest tightness, and coughing.
Association: when one characteristic is related to another and they change predictably together.
Bias: deviation of results or inferences from the truth, or processes leading to such systematic deviation. Any trend in the collection, analysis, interpretation, publication, or review of data that can lead to conclusions that are systematically different from the truth.
Case: a person in a study who has the particular disease or condition that is being studied.
Case-Cohort Study: includes cases of diseases of interest and a random sample of the entire cohort theoretically selected prior to knowing who will be a case. The referent cohort becomes a representative sample of the person-time experience of the entire cohort during the specified study period. The advantage of this methodology over a case-control study design is the ability to evaluate several outcomes with one referent sample.
Case-Control Study: a type of observational and analytical study. Enrollment into the study is based on presence (“case”) or absence (“control”) of disease. Characteristics such as previous exposure are then compared between cases and controls.
Cause: a factor or event that produces a second event.
Cause Specific Mortality Rate: the mortality rate from a specified cause for a population.
Chronic bronchitis: is a chronic inflammation of the bronchi (medium-size airways) in the lungs. It is generally considered one of the two forms of chronic obstructive pulmonary disease (COPD). It is defined clinically as a persistent cough that produces sputum (phlegm) and mucus, for at least three months in two consecutive years.
Chronic obstructive pulmonary disease (COPD): is a August 6, 2013 This leads to a limitation of the flow of air to and from the lungs causing shortness of breath.
Cohort: a group of people that may share a common characteristic (i.e., they live in a certain town or were born in a certain year) and who are enrolled in a study. The group has their health status followed for a period of time.
Cohort Study: a type of observational and analytical study. Enrollment into the study is based on exposure characteristics. Death, disease or other health related outcomes are then ascertained and compared.
Computerize Tomography (CT or CAT scan): non-invasive medical test that combines special x-ray equipment with sophisticated computers to produce images of the inside of the body. CT scans of internal organs, bone, soft tissue and blood vessels provide greater clarity and reveal more details than regular x-ray exams.
Controlled Variables: variables that are kept constant to prevent their influence on the effect of the independent variable on the dependent. Every experiment has a controlling variable, and it is necessary to not change it, or the results of the experiment won't be valid.
Confounder or confounding variable: is an extraneous variable in a statistical model that correlates (positively or negatively) with both the dependent variable and the independent variable. The methodologies of scientific studies therefore need to control for these factors to avoid what is known as a type 1 error: A 'false positive' conclusion that the dependent variables are in a causal relationship with the independent variable. Thus, confounding is a major threat to the validity of inferences made about cause and effect, as the observed effects could be attributed to the confounder rather than the independent variable.
Cross Sectional Study: a research method that involves observation of some subset of a population at a single point in time. It can be used to assess the prevalence of acute or chronic conditions in a population. It can provide a “snapshot” of the frequency and characteristics of a disease in a population at a particular point in time.
Crude Mortality Rate: the mortality rate from all causes of death for a population.
DLCO: the test used to determine the diffusing capacity of the lung for carbon dioxide. DLCO is the extent to which oxygen passes from the air sacs of the lungs into the blood.
Dependent Variable: is the event studied and expected to change when the independent variable is changed.
Descriptive Epidemiology: the aspect of epidemiology concerned with organizing and summarizing health-related data according to time, place and person.
Distribution: the frequency and pattern of health-related characteristics and events in a population.
Emphysema: is a chronic obstructive pulmonary disease. Emphysema is characterized by loss of elasticity of the lung tissue. Symptoms include shortness of breath on exertion and later at rest, hyperventilation, and an expanded chest.
Epidemic: the occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time.
Epidemiology: the use of medical science and statistics to track population health and to find causes of diseases in groups of people. Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to control health problems.
High Risk Group: a group in the community with an elevated risk of disease.
Incidence: the number of new cases of a disease in a defined population.
Incidence Rate: a measure of the frequency with which an event, such as a new case of disease, occurs in a population over a period of time.
Independent Variable: an exposure, risk factor, or other characteristic being observed or measured that is hypothesized to influence an event or manifestation (the dependent variable).
Inference: the development of generalizations from sample data.
Institutional Review Board (IRB): An institutional review board (IRB), also known as an independent ethics committee (IEC) or ethical review board (ERB) is a committee that has been formally designated to approve, monitor, and review research involving humans with the aim to protect the rights and welfare of the research subjects. An IRB performs critical oversight functions for research conducted on human subjects that are scientific, ethical, and regulatory.
Malignant: is a medical term used to describe a severe and progressively worsening disease. The term is most familiar as a description of cancer. Malignant tumor is synonymous with cancer.
Measure of Association: a quantified relationship between exposure and disease; includes relative risk, rate ratio and odds ratio.
Morbidity: illness, sick or unhealthy
Mortality: death, usually the cause (a specific disease, a condition, or an injury) is stated.
Mortality Rate: a measure of the frequency of occurrence of death in a defined population during a specified interval of time.
Non-response: in survey sampling many of the individuals identified as part of the sample may be unwilling to participate or impossible to contact. In this case, there is a risk of differences, between (say) the willing and unwilling, leading to selection bias in conclusions. This is often addressed by follow-up studies which make a repeated attempt to contact the unresponsive and to characterize their similarities and differences with the rest of the frame. The effects can also be mitigated by weighting the data when population benchmarks are available.
Observational Study: a study in which nature is allowed to take its course. Changes or differences in one characteristic are studied in relation to changes or differences in other, without the intervention of the investigator.
Odds Ratio: a measure of association which quantifies the relationship between an exposure and health outcome from a comparative study. It is defined as the ratio of the odds of an event occurring in one group to the odds of it occurring in another group, or to a sample-based estimate of that ratio. An odds ratio of 1 indicates that the condition or event under study is equally likely in both groups. An odds ratio greater than 1 indicates that the condition or event is more likely in the first group. And an odds ratio less than 1 indicates that the condition or event is less likely in the first group.
Period Prevalence: the amount of a particular disease present in a population over a period of time.
Phlegm: (pronounced / ˈ flεm/ ) is sticky fluid secreted by the mucus membranes and is limited to the mucus produced by the respiratory system (airways, lungs, and the respiratory muscles).
Pneumonia is an inflammatory illness of the lung. Typical symptoms associated with pneumonia include cough, chest pain, fever, and difficulty in breathing.
Prevalence: the number of cases of a given disease or other condition in a given population.
Prevalence Rate: the proportion of persons in a population who have a particular disease at a specified point in time.
Protocol: is a document that describes the objective(s), design, methodology, statistical considerations, and organization of a study. The protocol usually also gives the background and reason the trial is being conducted. The protocol describes, among other things, what types of people may participate in the trial; the schedule of tests, procedures, medications, and dosages; and the length of the study.
Public Health: an effort organized by society to protect, promote, and restore the people's health. Physicians treat one patient at a time; public health workers treat whole populations.
Respiratory System: In humans the respiratory tract is the part of the anatomy that has to do with the process of respiration. The respiratory tract is divided into 3 segments:
- Upper respiratory tract: nose and nasal passages, sinuses, and throat or pharynx
- Respiratory airways: voice box or larynx, trachea, bronchi, and bronchioles
- Lungs: respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
Most of the respiratory tract exists merely as a piping system for air to travel to the lung.
Risk: the probability that an event will occur (e.g., that an individual will become sick or die) within a stated period of time or at a particular age.
Risk Factor: conditions or exposures that can influence the chances that we stay healthy, develop a disease, or die prematurely. Some risk factors are impossible for us to change, like our genes. Other risk factors we can change. The latter are called modifiable risk factors, and include things like our diet, exercise habits, and smoking.
Random Sample: also known as a probability sample, a sample where the probability that any individual member from the population being selected as part of the sample is exactly the same as any other individual member of the population. It is the best way to avoid a biased or unrepresentative sample.
Rate Ratio: a comparison of two groups in terms of incidence rates, person-time rates, or mortality rates.
Relative Risk or Risk Ratio: is a ratio of the probability of the event occurring in the exposed group versus a non-exposed group.
Representative Sample: a sample whose characteristics correspond to those of the original population or reference population.
Sample: a subset of a population. Typically the population is very large, making a complete enumeration of all the individuals in the population impossible. The sample represents a subset of manageable size. Samples are collected and statistics are calculated from the samples so that one can make inferences or extrapolations from the sample to the population.
Science Advisory Board: panel of experts that give objective advice on technical subject matter.
Sensitivity: the ability of a system to detect epidemics and other changes in disease occurrence; the proportion of persons with disease who are correctly identified as having disease.
Specificity: the proportion of persons without disease who are correctly identified as not having disease.
Spirometry: (meaning the measuring of breath) is the most common of the Pulmonary Function Tests (PFTs), measuring lung function, specifically the measurement of the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.
Sputum is matter that is turned out from the respiratory tract, such as mucus or phlegm, mixed with saliva, which can then be spat from the mouth.
Standardized Mortality Ratio or SMR in epidemiology is the ratio of observed deaths to expected deaths, where expected deaths are calculated for a typical area with the same age and gender mix by looking at the death rates for different ages and genders in the larger population. The SMR may be quoted as either a ratio or a percentage. If the SMR is quoted as a ratio and is equal to 1.0, then this means the number of observed deaths equals that of expected cases. If higher than 1.0, then there is a higher number of deaths than is expected. An example might be a cohort study into cumulative exposure to arsenic from drinking water, whereby the mortality rates due to a number of cancers in a highly exposed group (which drinks water with a mean arsenic concentration of, say 10mg) is compared with those in the general population. An SMR for bladder cancer of 1.70 in the exposed group would mean that there is 70% more cases of death due to bladder cancer in the cohort than in the reference population (in this case the national population, which is generally considered not to exhibit cumulative exposure to high arsenic levels). The SMR may well be quoted with an indication of the uncertainty associated with its estimation, such as a confidence interval (CI) or p value, which allows it to be interpreted in terms of statistical significance.
Stratified Sampling: where the population embraces a number of distinct categories, the frame can be organized by these categories into separate "strata." A sample is then selected from each "stratum" separately, producing a stratified sample. The two main reasons for using a stratified sampling design are (1) to ensure that particular groups within a population are adequately represented in the sample, and (2) to improve efficiency by gaining greater control on the composition of the sample. In the second case, major gains in efficiency (either lower sample sizes or higher precision) can be achieved by varying the sampling fraction from stratum to stratum.
Surveillance: the systematic collection, analysis, interpretation and dissemination of timely health information, to gain knowledge of the pattern of disease occurrence and potential in a community, in order to prevent disease in the community.
Validity: the degree to which a measurement actually measures or detects what it is suppose to measure.
Vital Statistics: systematically tabulated information about births, marriages, divorces and deaths, based on registration of these vital events.