3: Mortality & Survival Flashcards
What can measures of mortality & survival tell us?
Mortality: public heath & heathcare priorities, how big a problem is in a population
Survival; effectiveness of heathcare & cancer control
What must be defined to measure cancer mortality?
Death
Population
Time period
Give a few examples of different ways cancer mortality can be measured
- all cause deaths
- cancer specific deaths
- general population at risk
- cancer patient population
How do you calculate all-cause mortality rate?
No. Of death (all causes) in population over time (t)
/
Total person-time at risk
How do you calculate cancer specific mortality rate?
No. Of deaths (cancer specific) in population over time (t)
/
Total person-time at risk
How do you calculate annual mortality rates?
No. Of deaths from cancer of interest in defined population in 1 year
/
Mid-year population in the same year
T or F:
- cancer survival is calculated from cancer onset to death
- cancer survival can be used as a prognosis for individuals
- survival analysis is also known as ‘time-to-event’ analysis
- F: from cancer DIAGNOSIS to death
- F: it is not a prognosis, only an average
- T
Describe the requirements in order to calculate survival anaylsis?
Well defined:
- case: eg cancer site, histology, stage, sex
- starting point: diagnosis, treatment, admission to hospital
- outcome: death (recurrence, treatment complication)
What is the best way to display survival time graphically?
Showing by time since diagnosis is preferred over calendar year as it is easier to compare similar points in cancer natural history between patients
How do you calculate the survival probability of a specific year?
Probability of survival = number of people alive in that year (given they have survived previous years) / total number of patients
How do you calculate cumulative survival probabilities?
Calculate probability of survival in each consequetive years and multiply together
On a Kaplan-Meier table, what is on the x and y-axes?
X: years
Y: survival probability
Why are Kaplan-Meir tables often preferred over actuarial life tables?
They should a stepped line rather than survival curve
This means no values are estimated
T or F:
- Kaplan-Meier graphs cannot compare 2 groups
- When comparing groups, the cumulative survival probability is the same for each group
- Groups are defined by sex, stage, histology, etc
- F: they can be used for comparisons
- F: survival probabilities are calculated separately
- T
What is the advantages for cancer-specific survival?
- for overall survival, there is no distinction from cancer and other causes of death
- cancer-specific takes into account competing causes of death
- easier to understand the cancer-specific risk to patients
How do you calculate relative/ net survival?
Observed survival in cancer patients
/
Expected survival in general population
What is relative survival?
The survival adjusted for the probability of dying from other causes that aren’t;;t cancer-specific
Use lung cancer in women from 1981-2009 in Sweden and England to describe the importance of joint interpretation
- between these years, mortality rates increased in Sweden, and decreased in England
- using only mortality, you may assume Sweden has less superior lung cancer treatment/ facilities
- incidence rates showed correlation to mortality, increasing in Sweden and decreasing in England.
- as lung cancer patients tend to die within a year of diagnosis, we can see that there was an increasing burden of disease in Sweden, and a decreasing burden in England.
- the survival rate in Sweden is higher than England, disproving the original hypothesis
What can’t we say the decline in mortality from 1990 in breast cancer was due to the introduction of screening?
- screening will not show a change in statistics straight after introduction
- the time between diagnosis, treatment, and death is long for breast cancer (compared to other cancers), decoupled mortality and incidence
What the are + and - of incidence as a statistic?
+ insights into cancer etiology ( causes)
+ can employ cancer registry data, strict quality control
+ unaffected by changes in treatment/ survival
- influenced by screening & improvments in diagnosis
- affected by changing definitions
What are the + and - of mortality as a statistic?
+ vital to inform public heath and heath-care priorities
+ information widely available from deaths registries
+ can be proxy for incidence in rapidly lethal cancers
+ can help evaluate effectiveness of treatment
- affected by trends in incidence & survival
- delayed reflection of progress in cancer survival
- subject to accuracy of death certification
Explain why age must be standardized when looking at data, using stomach cancer in colombia and England as an example
- when looking at all ages, Colombia looks to have a lower incidence (19.9) than England (33.9)
- 84% of clombia’s population is below 44 years old whereas England has an overall older population
- stomach cancer has a higher incidence in older population
- when using age-standardized data, Colombia has a higher incidence compared to England
