Diseases that cannot be passed from person to person
Diseases can cause ill health, which is defined as the state of physical and mental well-being
Causes of ill health
Communicable diseases
Non-communicable diseases
Poor diet
High levels of stress
Working with harmful chemicals
People with a defective immune system (e.g. HIV)
Are much more likely to suffer from infectious diseases (e.g. TB)
Infection with HPV (human papilloma virus)
Can cause cervical cancer
Infection with a pathogen
Can trigger an allergy (e.g. asthma, dermatitis)
Physical illness (e.g. arthritis)
Can trigger a mental illness (e.g. depression)
Non-communicable disease
Diseases not spread from person to person, instead caused by risk factors
In the 1930s, rate of lung cancer began to increase sharply and scientists couldn't explain this
Scientists could not carry out experiments on humans to try to work out what causes lung cancer as that would be unethical
Epidemiology
Studying the patterns of disease to determine risk factors
Lung cancer is much more common among cigarette smokers than among non-smokers
Scientists look at how many cigarettes people smoked each day and then how many of these people developed lung cancer
Correlation
A link between two variables
A correlation does not prove cause, it simply suggests that two variables might be linked
As the number of cigarettes smoked per day increases
The risk of developing lung cancer also increases
Positive correlation
When two variables increase or decrease together
As the number of years that a person smoked increases
The risk of developing lung cancer also increases
Causal mechanism
The scientific explanation for how a risk factor can cause a disease
Cigarette smoke contains chemicals which damage DNA and increase the risk of cancer, these are called carcinogens
Sampling
Investigating a group of people to draw conclusions about the whole population
Ideally, we'd look at every single person in a population to investigate a disease-diet link, but in practice it's not possible to sample every single person
If we select our sample from only one town, it's possible that this does not represent the entire population of the country, so the sample is biased