Age-Standarized Mortality Rate (SRATEs)
Definition:
The SRATE is a single, summary rate that allows a comparison of mortality or morbidity rates among populations or within a population over time. The numerical value of the SRATE is not meaningful by itself; it should only be used for comparisons over geography or time. The choice of a standard population can affect the standardized rates. A standard population with an age structure similar to the population of interest is most appropriate. The 1991 adjusted Canadian population is recommended for the standard population for SRATEs (see Appendix 4). SRATEs cannot be compared when different standard populations are used. The SRATE cannot be calculated if the age-specific rates of the study population (local area) are unavailable or are unstable due to small numbers. The SRATE should also not be used if the age-specific rates in the populations being compared do not have a consistent relationship.
Method of Calculation:
SRATE = summation (r * P) / (summation P)
Variance = summation [(r * (1-r) / q) * (P * P)] / [(summation P) * (summation P)]
Lower Interval = (SRATE - (1.96 * (square root of Variance)) * 1000
Upper Interval = (SRATE + (1.96 * (square root of Variance)) * 1000
Where:
"r" is the age-specific death rate in the local area (e.g., public health unit)
where r = d / q
"d" is the number of deaths in age group i of the local area population (e.g., public health unit)
"q" is the number of persons in age group i of the local area population (e.g., public health unit)
"P" is the number of persons in age group i in the standard population
(use 1991 Canada-adjusted population estimates)
Note:
For cancer incidence data, replace "death rate" with "cancer incidence rate" and "deaths" with "cancer incidents". For hospitalization data, replace "death rate" with "hospitalization rate" and "deaths" with "hospitalizations".
Standardized Mortality Ratio, Standardized Incidence Ratios and Standardized Hospitalization Ratios (SMRs, SIRs, SHRs)
Definition:
The SMR is a single, summary ratio that allows a comparison of mortality rates among two different populations. An SMR of 1.0 implies that the rates are the same for the population of interest and the standard population. An SMR > 1.0 implies that the rate is greater for the population of interest compared to the standard population. An SMR < 1.0 implies that the death rate is lower for the population of interest compared to the standard population. The standard population should be the Ontario population corresponding to the years of data that are being examined. The SMR is used when age-specific rates are not available and/or unstable due to small numbers for the population of interest.
Method of Calculation:
SMR = (summation o) / (summation M * q)
i.e., observed / expected
Variance = summation [(q * m * (1-m)] / [(summation q * M) * (summation q * M)]
OR
Variance = SMR / [summation (q * M)]
Lower Interval = (SMR - (1.96 * (square root of Variance))
Upper Interval = (SMR + (1.96 * (square root of Variance))
Where:
"o" is the observed number of deaths in a local area (e.g., public health unit) for the persons in age group i
"q" is the number of persons in age group i of the local area population (e.g., public health unit)
"M" is the age-specific death rate in the standard population (i.e., Ontario) for persons in age group i
"m" is the age-specific death rate in the local area (e.g., public health unit) for persons in age group i in the Standard Population
Note:
For cancer incidence data, replace "death rate" with "cancer incidence rate" and "deaths" with "cancer incidents". For hospitalization data, replace "death rate" with "hospitalization rate" and "deaths" with "hospitalizations".
Preventive Screening
Screening programs are the classic secondary prevention programs of Public Health. Their purpose is not to keep a disease process from starting, but to reverse or detain a disease process after it has already started. The primary objective of a screening program is to find and treat individuals in the early stages of disease. Most screening programs employ a minimally invasive, but imperfect, test to "screen" a population. Those who are culled by the screen have a high likelihood of being in an early stage of disease. They then receive a more thorough and expensive diagnostic evaluation as to whether or not they are in the early stages of disease.
A disease must have certain characteristics in order for screening to be a useful means of controlling that disease.
- People must stay in the early stages of disease long enough so that they can be detected by a screening program while they are still in that stage. Diseases that progress rapidly from their onset to a symptomatic state that should occasion medical care are not candidates for a screening program.
- There must be something that can be done for people correctly identified as in the early stages of disease so that they are either cured or their progression to more serious illness is stopped or slowed. It is not just the duration of the asymptomatic stage which is important. It is the duration of stage of disease which is both detectable and treatable that is important.
- The screening test must a) detect individuals early in the asymptomatic state, b) be socially acceptable, and c) be economically acceptable. A test that picks up individuals only toward the end of the asymptomatic state will not be acceptable. Neither will a test that is too invasive or too expensive.
- The incidence of disease must be high enough so that the yield of cases prevented by the screening program justifies its cost. If the incidence in the overall population is too low, then one might identify a sub-population with a high enough incidence to justify a screening program.
- The consequences of a positive screening test for individuals who do not have the disease must not be too severe for those individuals or for society. Even when the overall benefit of a program to society may be great, society is often reluctant to support a program that harms individuals who would not otherwise be harmed.
- There must be some therapeutic or preventive advantage to identifying individuals in an early disease state as opposed to the disease state where they would be identified without a screening program. If the case detected in the early stage of asymptomatic disease would have been detected and cured soon after the onset of symptoms, then less has been gained than if the symptomatic stage is essentially incurable. Likewise if there is no treatment regardless of the stage of disease, then screening will not help.
LGL/KFLA/HPE
This is the combined regions of Leeds, Grenville and Lanark, Kingston, Frontenac, Lennox and Addington, and Hastings and Prince Edward. This is the one of the health planning regions that were created for sampling in the 1996 Ontario Health Survey. There were 23 of these health planning areas in total created to cover the entire province.
Crude Death Rate and All-Cause Mortality
Definition:
The crude death rate is the total number of deaths relative to the total population (usually expressed per 1,000). All-cause mortality by age group is the annual number of deaths in a given age group per the population in that age group (usually expressed per 100,000).
Method of Calculation:
Crude Death Rate:
total number of deaths * k
total population
All-Cause Mortality by Age Group:
annual number of deaths in an age group * k
total population in that age group
Uses:
- Hypothesis generation.
- To set health objectives.
- To compare over time and place
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