Frequency Of Disease Flashcards
What is prevalence?
The proportion of people with a disease or condition in a given population at a specified time
What are the different types of prevalence?
Point prevalence
Period prevalence
What is point prevalence ?
Prevalence and data which has been collected at a single point in time
What is period prevalence?
Prevalence and data that has been collect of a period of time-less commonly used
What may a high and low prevalence reflect?
High prevalence - high risk population, prolonged survival without cure
Low prevalence - low risk population, rapid cure
What does incidence mean?
The number of new cases of a disease or condition that occur in a given population over a specified period of time
-indicates risk
What is a population ?
A group of people with a common characteristic
E.g a place, time, age, gender, occurrence of a life event
What are the 2 types of membership ?
Permanent membership
Transient membership
What is a population with a permanent membership ?
A population with a permanent membership is ‘fixed’ or ‘closed’
-e.g people who lived in Stoke on the 1st of January 2017
What is a population with a transient membership?
A population with a transient membership is ‘dynamic’ or ‘open’
-e.g the population of Stoke
What is the most common measure of frequency?
Count
-often expressed as an integer (number of people with the disease)
How is ratio calculated ?
One number dived by another ( x/y )
How is proportion calculated ?
Number dived by all ( x/ x+y )
-often expressed as a percentage
How is rate of disease calculated ?
Cases divided by total population x time ( x/x+y times 1/t )
E.g 1 out of 50 women per year
What are the benefits of estimation of prevalence?
Determine of sickness load
Planning health services
Examining health behaviours
What are the 2 types of incidence ?
Incidence proportion
Incidence rate
What is incidence proportion?
The proportion of people who develop a disease during a specific period of time
-cases per population
What is incidence rate ?
The rate at which people develop a new disease during a specific period of time
-cases divided by person time ( cases per person per year )
How do you calculate person time?
Sum of the total time contributed by all subjects
-the time a person is not infected for
What is case fatality rate?
Proportion of cases of a particular disease who die during a specific time period
What is crude mortality rate?
Proportion of people that die in a population during a specific time period
-Number of deaths divided by total population
What is an ecological study ?
A study in which the unit of analysis is the population and not the individual
E.g different countries, different ethnic groups
What are the strengths and weaknesses of an ecological study ?
Strengths: simple and cheap, good at hypothesis generating, assess outcomes on a population rather than the individual level
Weaknesses: potential for ecological fallacy (making wrong assumptions on an individual based on a population ) , misses possible effects in small subgroups
What is a cross sectional study?
A snapshot of health at an individual period of time
E.g prevalence of smoking in adult population in 1948
What are the strengths and weaknesses of cross sectional survey?
Strengths : quick and inexpensive, useful for estimating size of problem, potential for a large population size if data collection method is simple
Weaknesses: tendency to selectively include problems with long duration, susceptible to non-response bias (doesn’t include those who don’t respond)
What is a case control study?
A type of study in which two existing groups differing in outcome are identified and compared on the basis of some casual attribute
E.g people with lung cancer compared to people without lung cancer but are similar in every other factor
-look back at the hypothetical cause of the disease
What are advantage of case controls ?
Useful for rare outcomes, they can be done quickly, useful for outcomes in which there is a long period since exposure
What are the disadvantages of case controls ?
Only one outcome is assessed so are highly specific to a disease, measurement of exposure is often wrong or inaccurate (has bias)
What is a cohort study?
Like a cross sectional study but is across time
-look at the exposed and non exposed and the outcomes of interest
What are the advantages and disadvantages of cohort studies ?
Advantages: investigators multiple outcomes, minimise recall bias ( more frequent questionnaires),
Disadvantages: expensive and time consuming, inefficient for rare outcome, potential selection bias (people drop out etc)
What is an intervention study ( like a random clinical trail )?
Used to determine the effectiveness of an intervention like a drug/treatment
-give some the drug and some a placebo (determine that with non bias-randomised) Single or double blinded trails
What are the advantages and disadvantages of a random clinical trial?
Advantages: best method for evaluating effectiveness of drug, bias minimised, explains cause and effect
Disadvantages: difficult, time consuming and expensive, ethical restrictions, non-compliance of controls threatens validity
What is the difference between primary and secondary data?
Primary- collected first hand by the investigator for a specific purpose
Secondary- data has already been collected, and is used by someone else for a different purpose
What is ecological fallacy?
The error of making inferences about individual behaviour from aggregate data
A longitudinal or prospective study is also referred to as what study?
A cohort study
