HadPop - Lecture 3 Flashcards
What is a difference between an absolute and relative comparison?
Absolute comparison - a subtraction
Relative comparison - a ratio
What are the two types of comparison?
- Absolute
- Relative
What is another name for a absolute comparison?
A attributable risk
Define an attributable risk
The excess risk of developing the disease in a exposed group compared to the unexposed group.
What do relative comparisons tells us?
The strength of relationship between the exposure and disease
How do you calculate IRR
Number of new cases of disease in a particular area at a set time / total at risk person-time of observation.
How to calculate RR
cumulative incidence in exposed / cumulative incidence in unexposed.
What is a confounding factor?
Something that is independently associated with both the outcome and exposure but NOT present on the casual pathway.
Give an example of 2 general confounding factors?
Age
Gender
How can we adjust for confounding?
Design stage:
- Randomisation
- Stratification
- Restriction
Analysis stage:
- Standardisation
- Stratification
- Multi-variant analysis.
What is standardisation?
method of adjusting for age differences to make a valid comparison.
What are the two methods of standardisation?
- direct standisation
- in direct standisation
How do you calculate standardised mortality rate?
Total number of observed deaths in index population / total number of expected deaths in index population
How do you calculate standardised mortality rate?
Total number of observed deaths in index population / total number of expected deaths in index population
*X 100
If the SMR = 100 - then risk in the index population and reference population is the same
If the SMR > 100 - then the risk in the index population is higher.
Is SMR direct or indirect standardisation?
In-direct
What is a key feature of sampling?
Must be a representative of the population
What is a sampling frame?
A list of people from whom a sample was taken.
What are the two methods of sampling?
1) Random sampling
2) Non random sampling
Discuss random and non random sampling.
Random sampling = everyone in the sampling frame has a equal chance of being chosen, hence you obtain a representative sample.
Non-random sampling = this is easier and more convenient however, the sample may not be representative.
Describe the random sampling methods.
1) Simple random sampling - everyone is a number a they are selected randomly
2) Stratified sampling - Population split into two groups. People then picked from the group based on simple random sampling methods
3) Cluster Sampling - Using natural clusters in the population e..g school
4) Systematic sampling - Picking the Nth candidate.
What are the two types of errors and what are they?
Random error - A error which is due to chance ALONE
Systematic error - this is a error which is due to either sampling or measurement
Name the two main sources of bias and there subcategories:
1) Selection Bias
- Sampling bias (non representative sample)
- Non response bias
2) Instrument bias
- Equipment bias
- interviewer bias (due to things like training)
What is response rate?
the percentage of the selected sample that take part in the survey / study
Define precision
How close the results obtained are to each other
Define accuracy
How close are the results to the TRUE value.
What two components test the performance of your study?
1) Validity - How well did the test measure what it was suppose to measure
2) Repeatability - do you get the same results when redoing the experiment later on?
