Topic 5: measure of frequency in proportional measures Flashcards
(26 cards)
Define descriptive epidemiology
- To characterize distribution of disease by time/place/person
- It is 1st step to hypothesis concerning etiology = causes of disease
What are the 5 W of descriptive epidemiology?
1) What = diagnois
2) Who
3) Where
4) When
5) Why/how = causes/risk factors = hypothesis testing
Describe measure of disease frequency
- Assesses frequency of distribution of condition in population or health outcome
- Expresses as % = binary outcome = presence/absence of condition or mortality yes/no
Define frequency
- Not just number of events but also relationship of number to size of population
- The resulting rate = proportion = allow epidemiologist to compare disease occurrence across populations
Define rate
- Allows for comparison of disease + outcome frequency
- Between different sized populations + time periods + subgroups
Types of measures of disease frequncy
1) Prevalence
- Point
- Period
- Lifetime
2) Incidence
- Cumulative
- Rate
Describe point prevalence
- Proportion of population with disease at specified point in time e.g lung cancer in 1980
Proportion 0-1 or 0-100% - Estimated = number of existing cases at a given point in time over total study population
How to calculate the frequency for prevalence
Number of existing cases / Number of total population
Describe period prevalence
- Number of existing cases during specific time period compared to total population e.g. breast cancer in the past 10 years
- More applicable to chronic conditions
- Only appropriate to relatively stable conditions not acute disorders
Describe lifetime prevalence
- Proportion of population who at some point in life had condition
Define risk
- Individuals probibility of developing disease over time interval
Describe cumulative incidence
- Average risk in group of individuals
- Estimated = number of new cases during time period / total number at risk
- E.g. incidence recurrence of tumor in 5 years
How to calculate frequency for cumulative incidence
Number of new cases / Number of population initially at risk
What is the application of prevalence?
- Can display local/regional/global burdens of disease
- Can be used to compare disease frequency in different groups
What is the application of incidence?
- Incidence can be used to compare disease frequency in different groups
- Regularly documented incidence = inform about temporal/time trends in disease patterns
Describe pattern
- Occurrence of health-related event by time/place/person
- Time = annual/seasonal/weekly/daily/hourly
- Place = geographic variation + urban/rural differences + location of work/school
- Personal characteristics = age/sex/martial + socioeconomic status + environmental exposures
Explain mortality rate
- Most important measure of mortality
- Quantifies number of deaths in specific population during specific time period
How to calculate rate of mortality
Number of all deaths / Number of population at risk
Describe all cause mortality rate
- AKA crude mortality rate
- Takes into account all deaths from all causes in specified time period
How to calculate cause-specific mortality rate
Number of deaths from specific cause / Number of population at risk
How to calculate age-specific mortality rate
Number of deaths in specific age group / Number of population at risk
How to calculate case-fatality rate
Number of deaths from specific condition / Number of individuals with specific condition
What is the relationship between incidence + prevalence + mortality?
- Prevalence is determined by incidence + duration of disease = includes death/recovery rate
- If incidence is high + death low = high prevalence
- If high incidence + high death = low prevalence
How to calculate incidence rate
Number of new cases / person-time at risk
