Rod Jackson Flashcards
What is epidemiology?
The study of frequency (or occurrence) of dis-ease in populations
What does the term “dis-ease” mean?
Any health-related event or state - such as death and diabetes
What is an occurence?
The transition from a non-diseased state to a dis-eased state
What is a population?
Any group of people who share a common factor
What type of data is dealt with in epidemiological studies?
Quantitative
What are the types of quantitative data?
Categorical and numerical
What is categorical data?
Data grouped into categories e.g. man/woman
What is numerical data?
Data that takes on numerical values e.g weight and height
What are the visual components of the GATE frame?
Triangle Circle Square Arrow
What is the GATE frame?
Graph approach to epidemiology
What does the triangle represent in the GATE frame?
The participant population
It is divided into 3 parts:
Top = setting
Middle = eligible population
Bottom = Number of study population
What does the circle represent in the GATE frame?
Study specific sub-denominators = exposure group and comparison group
What does the square represent in the GATE frame?
The numerators (disease outcomes)
What does the arrow represent in the GATE frame?
Time
How do you deal with numerical data in the GATE frame?
They can either be converted to categorical data or average values can be calculated as dis-ease occurrence
What are the two measures of dis-ease occurrence?
Incidence and prevalence
What is incidence?
The measure of onsets of dis-ease occurring during a period of time from the population
What is represented by the vertical arrow?
Incidence - occurrence measured over a specified period of time
What is the equation to calculate incidence
Incidence = (Number of people in group who have dis-ease outcomes/Number of people in population)/Time taken for study
Incidence = (N/D)/T
Unit is outcomes per number of people per time taken for study
What is prevalence?
The measure of the number of people with the dis-ease at a point in time from the population
When is prevalence used?
When the dis-ease is not easily observable e.g. onset of diabetes cannot be easily measured
Also when the outcome can occur many times in a specified period of time e.g. asthma attacks
What does the horizontal arrow represnt?
Prevalence - the occurrence was measured at a point in time
What is the equation to calculate prevalence?
Prevalence = Number of people who have the dis-ease /Number of people in population at a point in time
Prevalence = N/D
Unit is the outcomes per people in the study at a specified point in time
What is the purpose of epidemiological studies?
To investigate and compare the EGO and CGO and in doing so estimate the association between the outcome and the exposure
What is relative risk RR?
EGO / CGO
no units
What does a RR value of 1 indicate?
EGO = CGO
What is risk difference RD?
EGO - CGO
units same as occurrence measure
What is PECOT?
Participants or study population Exposure group Comparison group Outcome Time
Memory aid for the 5 parts of epidemiological studies
What are the two types of errors?
Random and non-random
What are random errors?
Errors caused due to chance
What are non-random (systematic) errors?
Errors caused by problems with how the study was designed or conducted
What is RAMBOMAN?
Acronym used to identify where non-random errors can occur
Recruitment Allocation Maintenance Blind or Objective Measurements Analysis
How do systematic errors occur in the recruitment process?
- When a study on a population is done to approximate and apply the results to a wider population the study population must be recruited from the correct setting to represent the wider population - even in the correct process of sampling random error can occur
- The participants who meet the eligibility criteria from this setting must all be similar enough to fit into the same population
- The response rate (proportion of people in the eligible population who choose to take part in the study population) must be high enough so that there is no difference between those who accept to take part in the study and reject to take part in the study
How do systematic errors occur in the allocation process?
- Measurement error - EGO and CGO measured incorrectly meaning some participants will be allocated to the wrong group
- Confounding - when there are differences in the EG and CG other than the exposure that affect the study outcome (existence of confounders)
What is a randomised controlled trial?
Study in which the EG and CG are allocated randomly
In theory the two groups formed would be very similar minimising confounding
What is baseline comparison?
Checking the EG and CG differences before a study is commenced
What is concealment of allocation?
A solution to confounding in RCTs where the randomising process can be tampered with. Involves prevention of any possible tampering through study design
How can confounding be reduced?
RCTs
Larger sample size
Stratified analysis (analysis based on differences between groups e.g. age-standardisation)
How do systematic errors occur in the maintenance process?
In the ideal study
- maintain exposure status
- not be exposed to other factors affecting outcome
- not drop out of study
Any comprised factors introduce maintenance error.
How do systematic errors occur in the Blind and Objective measurement process?
Any problem in study design when measuring outcomes will lead to systematic error
How is measurement error reduced?
Set outcome to be objective in that they can be measured easily and clearly
Blind the participants or investigators or both to the knowledge of the exposure
What is random sampling error and why does it occur?
Errors (deviations from the truth) that occur due to chance.
Random sampling errors occur because when investigating the effects of an exposure on dis-ease occurrence, everyone in the population cannot be included - hence, a sample is chosen to represent this population and this creates random sampling error.
How is random error reduced?
Increase sample size
Do repeats on measurements related to allocation and outcome
What does a 95% confidence interval represent?
There is a 95% chance the true value of the occurrence from the whole population is included in the range provided.
What does it mean if the confidence interval for EGO and CGO do not overlap?
Reasonable to assume that the difference is significant and true assuming no systematic error was present
What does it mean if the confidence interval for a calculated RR value includes 1?
The difference in the EGO and CGO is statistically insignificant
What does it mean if the CI for a calculated RD value includes 0?
Difference is not statistically significant
What is meta-analyses?
The combination of multiple studies to demonstrate whether or not the exposure has had a real effect
