This assignment will define epidemiology, list and describe some of its main aspects and assess the significance of those aspects for their effect on health promotion. The example of lung cancer will be used throughout.
Definition
Epidemiology is the study of how diseases are distributed among populations and the factors that affect this distribution. Epidemiologists try to predict risk factors that may lead to a particular disease and identify strategies that could be used to prevent its occurrence. (Naidoo & Wills 2008: 4)
The following questions drive epidemiology:
Who becomes sick or is most likely to be affected?
Why do particular people become sick?
When are people most likely to be affected?
Where has the disease occurred or is most likely to occur?
How effective are available treatments and preventative strategies?
(Crichton & Mulhall in Naidoo & Wills 2008:74)
Epidemiology has the following main aims:
To describe patterns of disease in the population, or the disease distribution, across age, gender and geography.
To indentify the aetiology, or determinant, of the disease: risk factors or prior events associated with the appearance of the disease or condition.
To analyse frequency, or how many cases occur, over a given period.
To provide the data needed for the planning of preventative measures and treatment.
Epidemiology is concerned with rates: the focus is on groups rather than individuals and aims to highlight trends. (Naidoo & Wills: 2008:74)
Epidemiology has two main approaches:
Descriptive Epidemiology is concerned with the patterns of distribution of disease according to people, place and time and uses mortality and morbidity statistics as well as population data.
Analytical epidemiology explores cause and risk factors and asks why did it happen?
Successful prevention rests on identifying risk factors which can be reduced or eliminated.
(Hubley & Copeman, 2008:40)
History
In the past epidemiology has helped to explain the transmission of diseases, such as cholera and measles, by discovering factors shared by individuals who became sick. Modern epidemiologists have contributed to an understanding of factors that influence the risk of heart disease and cancer, which account for most deaths in developed countries today. Epidemiology has established the causal association of cigarette smoking with heart disease and lung cancer; shown that AIDS is associated with certain sexual practices and demonstrated the value of mammography in reducing breast cancer mortality. (Sci Tech, 2009)
Aspects of Epidemiology
An aspect is a ‘part’ or ‘facet’ of a particular subject area.
Aspects of epidemiology which will be assessed are as follows: mortality and morbidity rates, statistical analysis, cohort studies, correlation, causation and questionnaire/survey.
Mortality and morbidity rates.
Mortality rate is a measure of the number of deaths (in general, or due to a specific cause) in a population. Data is collected from the compulsory registration of death and its cause. Cause is the disease or injury which initiated the train of events leading to death. Information can be divided according to age, gender and cause.
Morbidity rates are either the number of new cases of a disease (incidence) or all cases at a point in time (prevalence). Data is collected from hospitals and GPs and includes: cancer registrations, notification of infectious disease, sexually transmitted disease, HIV/AIDS and congenital anomalies. (Tones & Green: 2008:45).
A central tool of epidemiology is rate comparison: population data collected by census is used for this purpose.
Lung cancer: figures confirm that lung cancer has an enormous impact on national mortality and currently accounts for 7% of all deaths and 22% of all deaths from cancer in the UK
Incidence rates:
Lung cancer – UK
Males
Females
Persons
Number of new cases (UK 2006)
22,381
16,646
39,027
Rate per 100,000 population*
60.8
37.1
47.4
Number of deaths (UK 2007)
19,637
14,872
34,509
Rate per 100,000 population*
51.5
31.3
40.1
One-year survival rate (for patients diagnosed 2004-2006**, England)
27%
30%
–
Five-year survival rate (for patients diagnosed 2001-2006**, England)
7%
9%
–
(Cancer Research UK)
Cohort studies
A sample of people is followed overtime and their lifestyle and exposure to hazards and the incidence of disease is monitored. A cohort of people has a characteristic in common e.g. the same disease or the same employer.
Causation
The investigation of a relationship between one event and another by weighing up a body of evidence. A number of methods are used to investigate causation including cohort studies. Relative risk is the ratio of the rate of a disease to the number of those exposed to a risk factor. It indicates how likely it is that an individual exposed to a particular environmental or lifestyle factor will go on to develop a particular disease.
Lung cancer – The most famous example of a cohort study was the British Doctor’s cohort study. Dr Richard Doll enlisted forty thousand male Doctors and followed them for fifty years. The results published in the 1950’s showed that many more Doctors who smoked went on to develop lung cancer than those who did not.. The study provided clear evidence for a causal link between smoking and lung cancer. (Hubley & Copeman: 2008)
.
Correlation
Correlation is a statistical measurement of the relationship between two variables.
Lung cancer – research has shown a correlation between smoking and social class with people of less affluent groups smoking more. Correlation has also been demonstrated between the smoking habits of close family members: young people are more likely to take up the habit if their parents smoke.(Ewles:2005)
Questionnaire and survey
A set of questions addressed to a statistically significant number of subjects as a way of gathering information.
Lung Cancer: The 2005 general household survey indicated that manual workers start to smoke at an earlier age, with 48% of men and 40% of women in manual occupations regularly smoking by 16, compared with 33% of men and 28% of women in managerial and professional occupations. (Cancer Research UK)
Statistical analysis
Used to determine likelihoods or probabilities.
Lung Cancer – Statistical Analysis provides a wealth of data and information. Available smoking statistics include incidence of cancer linked to number of cigarettes smoked per day and history of smoking. Also smoking statistics by age, socio-economic group, ethnic group, geographical variations and children are published.
As an example, this graph illustrates the prevalence of smoking by age over three decades and shows the decline following the linking of smoking with cancer and the subsequent health promotion programme.
Today, tobacco consumption is recognised as the UK’s single greatest cause of preventable illness and early death with more than 114,000 people dying each year from smoking-related diseases including cancers. (Cancer research UK, 2009)
Before the dangers of cigarette smoking were widely known, smoking prevalence varied little by socio-economic group. Today there are clear differences due to the differential decline in smoking by social class that occurred in the 1970s and 1980s. By 2007, 25% of adults in manual occupations smoked compared to 16% of those in non-manual occupations.
(Cancer research UK)
The influence of these aspects of epidemiology on health promotion using lung cancer and smoking as an example.
The World Health Organisation (WHO) defines health promotion as “the process of enabling people to increase control over and to improve their health”.
The mortality rates for cancer in general, and in particular lung cancer, highlight this as a health issue of significant importance and worthy of focus and resources.
The Doll cohort study demonstrated the correlation between smoking and lung cancer. Naidoo & Wills in Key Topics in Public Health say, ‘The single most critical area for action to reduce cancer is smoking’.
It is estimated that 1 in 2 smokers will die of a smoking related illness. If current smokers can be encouraged to quit mortality will be reduced: discouraging young people from starting to smoke will reduce smoking-related deaths during the second half of the twenty-first century. (Cancer Research UK)
Health promotion to reduce the levels of lung cancer has therefore focussed on smoking cessation.
Health promotion strategies have three components: education, service improvement and advocacy. Using lung cancer and its correlation with smoking as the example again:
Education involves increasing awareness of the risks, the benefits of quitting and practical ways of stopping.
Service improvement involves actions of primary care such as clinics and availability of nicotine patches.
Advocacy involves enforcement of controls such as laws preventing sale of cigarettes to under 18s and the ban on smoking in public places. (Hebley & Copeman, 2008)
Statistics show which groups are more likely to smoke and the greater degree of risk they face. The correlation between smoking and social class, indicated by the Household survey, highlighted that smoking rates are highest amongst manual workers. The need to target this group is recognised in the Government white paper ‘Choosing Health: Making Healthier Choices Easier’ which sets a target for reduction of smoking prevalence in this group. Smoking is a key contributory factor to health inequalities between socio-economic groups in the UK and accounts for a major part of the differences in life expectancy between manual and non-manual groups and is a key focus of the current government. (Department of Health, 2009)
Other current priorities are; the very young who are ‘at risk of uptake’ and the problem of passive smoking.
Evidence suggests a correlation between young people smoking and the smoking habits of their parents. People who start to smoke in their teens do so because they adopt the social pattern of their family. The habit quickly becomes an addiction, which is very difficult to break. It is easier to stop a young person from starting to smoke than getting someone to quit. Specific measures are in place to focus on the very young including the banning of sales to under 18s. This group is also highly influenced by advertising and as a result TV advertising has been outlawed.
The effects of passive smoking on children, in particular, have been highlighted in a graphic T.V. campaign which demonstrates to parents the harm they are causing their children.
Examples of other, current, health promotion initiatives aimed at smoking cessation include:
* Point of sale promotion has been severely restricted.
* In July 200, the advertising of cigarettes at sporting events, including Formula 1, was banned.
* On July 1st 2007, it became illegal to smoke in a public place or workplace including pubs.
* All cigarette packets must carry a health warning covering a specific percentage of the front and back of the packet.
* Media campaigns have been graphic and disturbing. The ‘fish hook’ advert highlighted the controlling nature of tobacco.
Primary Care Trusts run cessation programmes, one to one support, group sessions, quit smoking helpline, education events in schools and provide free nicotine patches.
The government levies ever increasing taxation on cigarettes to increase prices and give a financial incentive to individuals to quit. (Ewles, 2005:63)
October 2009, MPs agreed a ban on cigarette vending machines. (BBC News, 2009)
Annual no-smoking day. (Nosmokingday,2009)
Epidemiological research also confirms the success, or otherwise, of health promotion strategies.
Between 1970-2000, British men experienced the most rapid decrease in death rates from lung cancer in the world as a result of the success of the health promotion measures and smokers quitting the habit.
(Ewles: 2005)
In the early 1900s, lung cancer was a rare disease causing fewer than 10 male deaths annually in every 100,000 men.
By the 1950s, the lung cancer death rate had risen six-fold, prompting the first epidemiological study that linked tobacco smoking and lung cancer in Britain. By the 1980s, the death rate for lung cancer was over 100 per 100,000 men. From the early 1980s onwards, following extensive focus of efforts on smoking cessation, the male lung cancer mortality rates have fallen continuously.
The striking mortality trends by age over the past fifty years for men in England and Wales are shown below:
(Cancer Research UK)
Conclusion
By identifying factors that increase the risk of disease, epidemiologists provide crucial input into the formulation of public health policy. (Sci Tech, 2009)
Measuring health is important for health promotion as it establishes priorities, assists in planning, enables prioritization of actions with high-risk groups, justifies use of resources and demonstrates the efficiency (or otherwise ) of health promotion initiatives. (Naidoo & Wills, 2009).
In many studies a categorical answer is never produced as there is never 100% proof of the outcomes, only evidence to suggest. For example, not everyone who smokes will contract lung cancer and some non-smokers do contract the disease. (Naidoo & Wills, 2005)
The epidemiological research which proved the link between smoking and lung cancer, and the subsequent health promotion strategies, have reduced the prevalence of smoking and consequently the incidence of lung cancer significantly over the last thirty years.
Health promotion priorities and strategies are continually reviewed as new ‘evidence to suggest’ is produced from ongoing epidemiological research.
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