Occurance of a disease - Chap 4 Flashcards
Mortality rate
Rate of Death from a specific disease over a period in time/ among the population at risk of developing the disease. If we are calculating the rate for 1 year population we need to take mid-year total population at risk in the denominator as the population generally fluctuates.
True Rate - has time in the denominator
People in the denominator have equal chance of being in the numerator
Mortality rate = Incidence rate
Case-fatality high
Disease duration short
e.g. Pancreatic cancer
Limitations of Mortality
- **Does not really specify the cause of death. **A person dying from car accident could have cancer or something which actually caused the death.
- Changes in the International Classification of Diseases definition
- Changes in Case definition (standard term to identify a case includes person, time, place
Case-fatality rate
Number of deaths due to a specific disease / Number of individuals diagnosed or affected by the disease
Denominator includes people who have the disease
Not a true rate as no time in the denominator
Difference between Mortality and Case-fatality rate
Mortality rate: denominator = entire population at risk of dying, including **those who have the disease + those who do not have** the disease but are at risk of developing
**Case-fatality: **denominator limited to those who “already have the disease”
Proportionate mortality
Annual number of deaths from a specified disease/Annual number of total deaths (all causes) *100
- What proportion of deaths can be attributed to a specific disease?
- It does not tell us about the risk of dying
- Because the denominator contains “all deaths from different causes”
- if death by one cause increases the proportion changes so it does not tell us about the risk of dying.
Crude vs Specific vs Adjusted Mortality Rates
**Crude: **total cases (deaths)/total population at a specified time period who have or do not have the disease
**Specific: **Taking the frequency specific to the particular sub-population e.g. Age specific, Race specific or gender specific
Adjusted: Accounts for the differences in the character specific structure of the population being compared. Population is standardised to [ a standard population] for comparision purposes. [only used for comparision purspose alone they are meaningless]
Indirect Age Adjustment (Standardized Mortality Ratios)
Used when age-specific mortality rates are unavailable. Observed no. fo deaths/Expected number of deaths per year. When the age adjustment is not know ; we apply the population age estimates.
SMR>1 (observed number of deaths is more than expected)
SMR<1 (observed number of deaths is less than expected)
Real changes in mortality rates
- Changes in survivorship without change in incidence
- Changes in incidence
- Changes in age compostion of the population
- All of the above
Changes in mortality that are not real (similar to limitations)
Numerator:
* error in diagnosi/case definition
* changes in ICD codings
* errors in age/gender or specific classifications
Denominator:
* errors in determining populaiton at risk
* erros in counting population at risk
* errors in classificaiton of population (specific classifcation age, gender etc.)
Years of Potential Life Lost (YPLL)
Measure of premature mortality; defined by OECD countries as any death before 75 years. The younger the age at which death occurs, the more years of potential life are lost.
We want this number to be low
Quality Adjusted Life Years (QALYs)
Combines survival and quality of life: QALY=Σ(utility score * year of life)
Ranges from 0 (death) to 1 (perfect health)
1 year of life in perfect health = 1 QALY
Disability Adjusted Life Year (DALY)
- Burden of disease measure
- DALY is the total of years of life lost (YLL) and years lived with disability (YLD): DALY=YLL + YLD
- 1 DALY is one year of healthy life lost
- Primarily used in international comparisons due to data availability
we want this to be low
When is YPLL - Years of potential life lost used?
- Establishing research and resource priorities
- Surveillance of temporal trends (seasonal / time-related) in premature mortality
- Evaluating the** effectiveness of program** interventions
When is QALY - Quality adjusted life years used?
- Used to plan short-term treatment programs
- Determine the effects of the treatment on their self-reported quality of life
- Establish priorities in situation of scarce health care resources
When is DALY - Disability adjusted life years used?
- Burden of disease measure
- 1 DALY is one year of healthy life lost
- Primarily used in international comparisons due to data availability
