Defining Abnormality Flashcards
Define Epidemiology
The study of distribution and determinants of health related states or events in specified populations and application of this study to control health problems
What is health
A state of complete physical, mental and social well- being and not merely the absence of disease or infirmity
What are three criteria for establishing abnormality
Abnormal as infrequent occurrence
Abnormal as associated with disease/death/disability
Abnormal as treatable
Describe the Statistical definition of Normal
Normal distribution:
Frequent (common as normal)
Within 2 SDs above and below mean
Describe the Statistical definition of abnormal
Values beyond 2 SDs above and below the mean
List four reasons that the statistical definition of Abnormal can be misleading
- Some illnesses more prevalent than others
- association with disease may be important only at extreme values
- some extreme values are beneficial
- some illnesses have no threshold at which risk of ill-health/ death starts
What is the equation for Sensitivity of a test for disease according to Gold Standard
a/a+c
Where
a: true positives
c: false negatives
What is the equation of Specificity of a disease according to Gold Standard
Specificity
d/b+d
Where
b: false positives
d: true negatives
What is the equation for percentage true positive values in a test for disease
a/a+b
Where a is true positive
b is false positives
What is the equation for percentage true negative values in a test for disease
d/c+d
Where c is false negatives and d is true negative
What us done to minimize false negatives in the test for disease
Cut-off shifted to minimize false negatives
Continuum shifted to the left
Ie optimise sensitivity
What are consequences of shifting the cut off to minimize false negatives
Specificity reduced
A negative result from a sensitive test rules out the diagnosis
What changes are made to minimize false positives in testing for disease
Cut-off shifted to the right to minimize false positives and optimize specificity
What are the consequences of minimizing false positives by shifting the cut off to the right
Sensitivity is reduced
Positive result from a specific test rules in the diagnosis
For the criterium that states “Abnormal =Treatable”
What is the point at which the individual is designated abnormal
At a point at which treatment leads to better outcome (treatment does more good than harm)
What is the basic premise of epidemiology
Disease does not occur at random, but pattern of disease reflects the operation of underlying factors
What is the significance of understanding the distribution of disease
We can understand the aetiogy of disease and therefore how OR if need to investigate, treat or prevent it
Define descriptive epidemiology
Study of the occurrence and distribution of disease
What is the difference between Descriptive and Analytic Epidemiology
Descriptive Epidemiology identifies and reports on both the frequency and pattern of health events (what who where when)
While
Analytic Epidemiology searches for determinants of health outcomes (how why)
What are the three objectives of Descriptive Epidemiology
Permit evaluation of trends in health and disease
Provide a basis for planning, provision and evaluation of health services
Identify problems to be studied by analytic method
What are the three pillars of Descriptive Epidemiology
Person
Place
Time
“Person” is a pillar of Descriptive Epidemiology
List aspects of Demographic
Age Sex Marital status Ethnic group Race Socioeconomic Status (social class, occupation,employment status, crowding)
“Person” is a pillar of Descriptive Epidemiology
List aspects of Lifestyle/Behavior
Alcohol Smoking Exercise Religion Stress Nutritional Status
Describe the significance of the pillar “place” in Descriptive Epidemiology
Where person was exposed or source of infection
- Geographical boundaries
- Clustering
- Effects of Migration
- International comparisons
Who is called the “Father of Epidemiology “
John Snow
What are the six types of time trends in Epidemiology
Seasonal Secular Periodic Endemic Epidemic Pandemic
Describe Seasonal time in relation to Epidemiology
Time variation related to seasons of the year
Describe Secular trends in relation to Epidemiology
Long term trends of disease
Describe Periodic time in relation to Epidemiology
Temporary interruption of the general trend of secular variations
Describe Endemic in relation to Epidemiology
Expected level of health events in a specific population in a defined area for that time
Describe Epidemic in relation to Epidemiology
Increase in incidence above the expected level in a defined geographic area within a defined time period
Describe Pandemic in relation to Epidemiology
A world wide epidemic affecting an exceptionally high proportion of the global population
What kind of chart is ideal for an Epidemiology curve
Histogram
List four Descriptive study designs for individuals
- Case Report
- Case Series Report
- Cross sectional report
- Surveillance studies
List one Descriptive study designs for populations
Ecological studies
What is a case report
A report of a single individual (or group of individuals with the same diagnosis)
What is an advantage of a case report
Cases can be aggregated from disparate sources to generate hypothesis and describe new syndromes
What is one limitation of case studies
Can’t test for statistical association because there is no relevant comparison group
Define cross sectional studies
AKA prevalence studies measure disease and exposure simultaneously in a well defined population
What are two advantages of cross sectional studies
Studies cut across the general population, not simply those seeking medical care
What are two limitations of cross sectional studies
You cannot determine whether exposure preceded disease
Since prevalent rather than incident cases determined, results will be influenced by survival factors
What is the purpose of Public Health Surveillance
Ongoing, systematic collection, analysis and interpretation of health-related data essential to the planning, implementation, and evaluation of public health practice, closely integrated with the timely dissemination of these data to those responsible for prevention and control
Describe Ecological Studies
These studies use measures that represent characteristics of entire populations (rather than a focus on individuals) to describe outcomes in relation to some factor of interest such as age, time, utilization of services or exposure
What are two major types of Ecological studies
Ecologic comparison (cross sectional studies) Ecologic trend studies
List two advantages of Ecological studies
Generates hypotheses for analytic studies
Can target high risk populations, time periods, or geographic regions for future studies
What are two limitations of Ecological studies
Group data - therefore cannot link disease and exposure in individuals
Avoid drawing inappropriate conclusions
What is Ecological Fallacy
The incorrect attribution of population level associations to individuals in a population
What is atomistic fallacy
The incorrect attribution of individual associations to population level associations
What are the 10 steps in outbreak Investigations
- establishing the existence of an outbreak
- preparing for fieldwork
- verifying diagnosis
- defining and identifying cases
- using descriptive Epidemiology
- developing hypotheses
- evaluating the hypotheses
- implementing control and prevention measures
- communicating findings
