Module 8.3 Flashcards
Incidence
Number of new cases reported in a specific time period
Prevalence
Number of people in a population that have been diagnosed with the disease over a certain time
Mortality
The number of people who have dies from the disease
Morbidity rate
The number of people who have become ill (incidence) and are ill at a given time (prevalence)
Epidemiology
Study of factors involved in the occurrence, prevalence and spread of disease in a population
Social value of epidemiology
without it public policy would never change
It offers the potential to save lives before the causes of disease are known
Find evidence of disease before the mechanisms of the disease are known, before lab studies
Endemic
a disease that is constantly present in a population but in relatively few persons e.g., leprosy
Outbreak
The occurrence of the disease in greater numbers than expected (above endemic)
can occur in a large or small region or in a specific location, like a school
Epidemic
An increase in the number of cases of a disease in a more widespread area than an outbreak
Pandemic
Endemic that occurs over large regions, like entire countries or continents
Burden of disease
A measure of the impact in a population of diseases, health conditions and injuries
measures difference between actual health of a population and the ideal situation of full health (‘health gap’)
Unit commonly used is DALY = disability-adjusted life years: summary of the years lost to disease (early deaths + years lived with ill health)
Every disease has a DALY value (different for each country)
Treatment of disease
take vitamins, minerals or nutrients
surgery
radiotherapy
Complex treatment: specialised medication (chemotherapy)
minimising risk factors
Management of symptoms (e.g., genetic diseases)
Future direction for treatment example
Lung cancer
- targeted therapy -> drugs designed to target only cancer cells by identifying special features of cancer cells
- Monoclonal antibodies -> antibodies produced in a lab (using live animals) that recognise and bind antigens in cancer cells (aka cancer-specific biomarkers) antibodies may carry an anticancer drug
immunotherapy -> using cancer cell markers to guide immune cells to recognise and kill cancer cells
Descriptive studies
Usually the first conducted when investigating cause of disease
provides information on pattern -> frequency, section of population affected
hypotheses are proposed about cause of disease
Analytical studies
after descriptive is complete
collects more data which is statistically analysed to test hypotheses as to the likely cause of disease
morbidity, mortality, incidence also used
Case control study:
- compare people with disease (cases) to people without disease (control) and look for differences in exposure to possible cause of disease
- large range of data is collected and analysed to determine likely cause
Cohort studies:
- involve studying two or more similar groups who are free of the disease
- these groups differ in one main factor: exposure to potential cause of disease
- one group is exposed, other is not
- groups followed over long period of time, to compare resulting incidence of the disease being studied
Intervention studies
used to test effectiveness of treatment or effectiveness of public health campaign
aim is to change behaviour of population in order to reduce the incidence of disease
Example: experimental study; used to test effectiveness of a new type of drug
- participants randomly placed in two groups; one receives trial and one receives placebo. Effectiveness is recorded and statistically analysed to determine effectiveness
Example: quasi-experimental study; researcher chooses the subjects who receive drug/treatments
Steps of epidemiology: cholera
Descriptive study:
- john snow went from door to door and recorded as much information as possible from the people
- He plotted the information and cases on a map
Analytical study:
- The information was studied, and anomalies were investigated
- He found that many people had the disease around a water pump -> he did a case and control study looking at people who did and didn’t have the disease
Intervention study:
- the pump was taken away and cholera reduced
Evaluating a method:
Is it representative of population? how was the sample selected?
Was the method an epidemiological method?
Where there flaws in design? -> selection bias, information bias
What was the control? was it valid?
- nobody knows who was affected if you were aware who would get a pill then psychologically the controls are invalid
How was data collected?
Are results reliable and statistically relevant?
Random errors in epidemiological studies
Random errors:
- unpredictable variation in data
- makes study less precise but does not skew data in a particular direction
- can be overcome by increasing sample size
Systematic errors in epidemiological studies
constant deviation from what the true value should be -> shifts study in a particular direction
Selection bias
- sampling bias: chosen subjects do not represent population
- volunteer bias: people who volunteer have a vested interest
- Healthy worker bias: participants who are working are generally healthier than those who aren’t
- Prevalence bias: only current cases included, recovered and dead should be as well
Information bias:
- errors in taking measurements
Misclassification bias: subjects with condition are undiagnosed at start of study
- Recall bias: ability to recall will be better in subjects with condition
- Ascertainment bias: not all members of same group followed equally
- interviewer bias: interviewer indirectly leads participant to answer
- Measurement bias: measurements are consistently inaccurate
- Loss to follow-up bias: not all subjects who began the study are available at the end
Examples of epidemiological studies: lung cancer
Richard Doll -1947 (London)
First one to suggest a link between lung cancer and smoking.
Type of study was case control. Compared patients with lung cancer and patients without lung cancer but other conditions.
Results showed that many of the patients with lung cancer were smokers.
Benefit: changed views of smoking and a gradual change in people’s perception and habits. Government regulation gradually followed over the last 50 years.
