Epidemiology

Epidemiology
Epidemiology is the study of the demographics of disease processes, including the study of epidemics and other diseases that are common enough to allow statistical tools to be applied. It is an important supporting branch of medicine, helping to find the causes of diseases and ways of prevention. It can, using statistical methods such as large-scale population studies, prove or disprove treatment hypotheses. Another major use of epidemiology is to identify risk factors for diseases. Epidemiological studies generally focus on large groups of people and relate to a target population that can be identified. This allows statistics to be used to recognize trends and possible causal factors. The three major epidemiologic techniques are descriptive, analytic, and experimental. While all three can be used in the investigation of disease occurrence, the method used most is descriptive epidemiology.
Once the basic epidemiology of a disease has been described, analytical methods can be used to study the disease further, and an experimental approach can be developed to test a hypothesis. In descriptive epidemiology, data that describe the occurrence of the disease are collected by various methods from all relevant sources. The data is then collected by time, place, and person. Four time trends are considered in describing the epidemiologic data: secular, periodic, seasonal and epidemic. A description of epidemiologic data by place must consider three different locations: where the individual was when disease appeared, where the individual was when he or she became infected from the source, and where the source became infected with the pathogenic agent. The third focus of descriptive epidemiology is the infected person. All relevant characteristics should be noted: age, sex, occupation, personal habits, socioeconomic status, immunization history, etc. Once the descriptive data has been analysed, the features of the disease should be clear enough that further areas for investigation are obvious. The second epidemiologic method is analytic epidemiology, which analyses disease parameters for possible cause-and-effect relationships. The two main analytical methods are the case-control method and the cohort method. The case-control method starts with the disease and works back to the cause that led to the effect. The cohort method studies two groups: one that has had contact with the suspected causal factor under study and a similar group that has had no contact with the factor. When both groups are observed, the effect of the factor should become apparent. Another analytic method is the cross-sectional study, in which a group of people is surveyed over a limited time frame to establish the relationship between a disease and variables present that may influence its occurrence. The third epidemiologic method is the experimental approach. A hypothesis is developed and an experimental model is developed in which selected factors are controlled. The effect of the manipulation will either verify or refute the hypothesis. For example, from 1993 to 1997, a group of researchers from Iowa studied 1,027 women: 413 who were newly diagnosed with lung cancer and 614 ?controls?, women aged 40 to 84 who had lived in their homes for the past 20 years or more. The women studied in both groups included smokers as well as non-smokers. Women were studied because they typically have less occupational exposures to substances that may cause lung cancer, and historically have spent more time in the home. Problems in conducting epidemiological studies include: selection bias when choosing study groups; recall bias (the study group not recalling habits or events accurately); misclassification of data; and confounding data. These can lead to subjective studies, misleading results and inconclusive inferences. Proper interpretation of data requires past as well as present information about the occurrence of the disease. The regular collection, collation, analysis and reporting of data is essential for proper interpretation. One area of study that has been heavily documented the relationship between smoking and lung cancer. Cigarette smoking is by far the leading cause of lung cancer, accounting for approximately 90% of lung cancer cases in the United States and other countries where cigarette smoking is common, such as Australia. Compared to non-smokers, smokers have about a ten-fold increase in lung cancer risk at present. This table gives the number of deaths from various causes in a prospective study of cigarette smokers (?observed deaths?) compared with the number to be expected among non-smokers of the same ages (?expected deaths?). The differences between the two represent ?excess deaths?. The contribution of each disease to the total of excess deaths is given as the ?percentage of excess?. Dividing the number of observed deaths by the number of expected deaths gives the ?relative death rate? for each disease. Cause of Death Observed Deaths Expected Deaths Excess Deaths Percentage of Excess Relative Death Rate Total deaths (all causes) 7316 4651 2665 100.0 1.57 Coronary artery disease 3361 1973 1388 52.1 1.70 Other heart disease 503 425 78 2.9 1.18 Cerebrovascular lesions 556 428 128 4.8 1.30 Aneurysm & Buerger?s disease 86 29 57 2.1 2.97 Other circulatory diseases 87 68 19 0.7 1.28 Lung cancer 397 37 360 13.5 10.73 Cancer of mouth, larynx, or esophageus 91 18 73 2.7 5.06 Cancer of the bladder 70 35 35 1.3 2.00 Other cancers 902 651 251 9.4 1.39 Gastric & duodenal ulcer 100 25 75 2.8 4.00 Cirrhosis of the liver 83 43 40 1.5 1.93 Pulmonary disease (except cancer) 231 81 150 5.6 2.85 All other diseases 486 453 33 1.2 1.07 Accident, violence, suicide 363 385 -22 -0.8 0.94 (Data from E. C. Hammond and D. Dorn, 1966.) In nsw in 2000, smoking caused an estimated 6,578 deaths overall, with 4,322 males and 2,256 females estimated to have died due to smoking. This represents 18.5% of all male 10.3% of female deaths respectively. In 1999-00 it is estimated that smoking caused 35,277 hospitalisations among males and 18,531 hospitalisations among females. This represents 4.0% of all male 1.8% of female hospitalisations respectively. The epidemiologic evidence and the corresponding biological understanding of respiratory cancer have supported the conclusion that smoking causes lung cancer. It is well documented that cigarette smoke: ? is the major cause of lung cancer (primary carcinoma of the lung). ? is a cause of heart disease, chronic lung disease, and oesophageal cancer. ? contributes to the development of cancer of the bladder, pancreas, and kidney. ? causes low birth weight in babies of women who use tobacco during pregnancy. ? contains more than 4,000 chemical compounds, at least 43 of which cause cancer in humans and animals. ? contains nicotine, which causes a chemical addiction to cigarette smoking through its effect on the nervous system. The risk of lung cancer among cigarette smokers increases with the duration of smoking and the number of cigarettes smoked per day. This observation has been made repeatedly in cohort and case-control studies. Risk models have been created to estimate how lung cancer risk varies with the number of cigarettes smoked, the duration of smoking, and age. In one widely quoted analysis, a model for lung cancer risk based on data from the cohort study of British physicians was composed. This model predicted a stronger effect of duration of smoking than of amount smoked per day. Thus, a tripling of the number of cigarettes smoked per day was estimated to triple the risk, whereas a tripling of the duration of smoking was estimated to increase the lung cancer risk 100-fold. Age-Specific Lung Cancer Mortality Rates per 100,000 People [image][image][image] Smoked 20 Smoked 40 Cigarettes per Day Cigarettes per Day Age Group, Never- [image][image] yr Smokers 30 Years 40 Years 30 Years 40 Years Men 50-59 2.5 124.6 236.8 188.4 336.5 60-69 11.9 224.3 486.8 572.8 606.6 Women 50-59 5.9 93.2 150.2 152.2 159.5 60-69 9.8 200.8 264.4 257.7 552.8 [image] Since public efforts to prevent smoking began 25 years ago, there has been a noticeable decrease in the rate of age-adjusted cancer death from lung cancer in white males (57 per 100,000 population). Unfortunately, in the past 50 years the number of women who smoke has increased, so the rate of cancer deaths in females continues to rise (26 per 100,000 female population). The 5 year overall survival rate for lung cancer has steadily increased from 8 percent in the 1960?s to 14 percent in the 1990?s. This improvement is thought to be a result of advances in combined-modality treatment with surgery, radiotherapy, and chemotherapy. The Quit campaign is a national government and non-government run program with the aim of reducing smoking rates in Australia. It combines advertising with:
A national ?Quitline? (telephone counseling and advice line)
service for smokers;
Partnerships with health and medical bodies;
The participation of doctors Australia-wide;
A campaign website;
National media promotions.
The federal government has dedicated $21.3 million to the campaign since 1996. State and territory Quit Campaigns are providing services to help smokers who want to quit. Most anti-smoking advertising campaigns warn smokers they are at risk of ill health or death. Unlike most anti-smoking campaigns that warn smokers that they at risk of ill health, the Quit campaign focuses on abstract concepts like risk and probability, providing graphic images of the health damage smoking can cause. The primary aim of this campaign is to encourage Australian smokers to quit now, instead of later. This idea is promoted through slogans and catch phrases such as ?Every cigarette is doing you damage?, "It?s not just a risk ? it?s a certainty that smoking will damage your health", and "Smoking damages your arteries, lungs and eyesight". Quit advertisements can be seen around Australia on television, radio, and newspapers and on buses and posters. This campaign is aimed at 18-40 year old smokers. A study examining changes in smoking prevalence in Australia during the 1980s has concluded that anti-smoking education campaigns have had a significant downward effect on smoking rates. The study observed prevalence trends prior to the commencement of, and following, the Sydney campaigns (initiated in 1983), and the Melbourne campaigns (initiated in 1984). These programs led to an immediate 2.6% drop in overall adult smoking rates, and a continued 1.5% decline annually among men. Prior to these campaigns there had been no observable trend in smoking prevalence in either city.

Epidemiology 7 of 10 on the basis of 2463 Review.