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Ministry of Health

TERMS, METHODS, AND COMPUTATIONAL EXAMPLES



ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS)

In 1987, the World Health Organization, in recognition of AIDS and the human immunodeficiency virus (HIV) that causes AIDS as important health concerns, added new codes to the International Classification of Diseases, Ninth Revision (ICD9) which allowed AIDS (042) and HIV (043-044) to be identified as unique causes of death and also provided differentiation among the complications of AIDS.


AGE-SPECIFIC FERTILITY RATE (ASFR)

The rate of live births per 1,000 women for the specific age group. This is a more detailed measure than the crude birth rate, as it reflects variations in the birth rate by age groups of the female population. (See Statistical Computation under Fertility Rate for an example.)


AGE STANDARDIZATION

Various measures are age standardized to account for compositional differences in populations, in order that more meaningful comparisons can be made between different time periods or geographic areas. Such measures may be calculated for both genders combined or separately by gender. The major age-standardized measures employed in this report are: Age Standardized Mortality Rate (ASMR), Standardized Mortality Ratio (SMR), Potential Years of Life Lost Standardized Rate (PYLLSR), and Potential Years of Life Lost Index (PYLLI). (See Statistical Computation for an example.)


AGE STANDARDIZED MORTALITY RATE (ASMR)

A summary of age adjusted death rates by gender which have been standardized to a specific population (such as the 1971 Canada Census) for the purpose of rate comparisons of different time periods or different geographic locations. ASMRs for males were standardized using the 1971 Canada male population while female ASMRs were calculated using the 1971 Canada female population. (See Age Standardization and Standard Population; for an example, see Statistical Computation.)


AIDS

(See Acquired Immunodeficiency Syndrome.)


ALCOHOL-RELATED DEATHS

Alcohol-related deaths are based on the ICD9 diagnostic categories listed below, for which the resulting deaths are directly or indirectly attributed to the use or abuse of alcohol.

ICD9
Code		 Diagnostic Category ICD9
Code		 Diagnostic Category
291 Alcohol psychoses 571.3 Alcoholic liver damage, unspecified
303 Alcohol dependence syndrome571.5 Cirrhosis of liver without mention of alcohol
305.0 Non-dependent abuse of alcohol571.9Unspecified chronic liver disease without mention of alcohol
357.5 Alcoholic polyneuropathy577.1Chronic pancreatitis
425.5 Alcoholic cardiomyopathy648.4"Alcohol and pregnancy"
535.3 Alcoholic gastritis760.7"Fetal Alcohol Syndrome"
571.0 Alcoholic fatty liver790.3 Excessive blood level of alcohol
571.1Acute alcoholic hepatitisE860 Accidental alcohol poisoning
571.2 Alcoholic cirrhosis of liver   


Alcohol is considered to be a direct cause of death if one of the above conditions is listed as the underlying cause of death on the medical certification of death. If, however, any of the above conditions are listed on the certificate as antecedent causes giving rise to the underlying cause or other significant conditions contributing to the death, the death is considered to be indirectly related to alcohol. ICD9 codes 648.4 and 760.7 include deaths due to substances other than alcohol. Only if alcohol is explicitly noted on the Medical Certificate is the Death considered to be alcohol-related for these codes. In 1993, the Medical Certification of Death form was revised to include a space to note environmental/occupational/lifestyle factors. As a result, the number of deaths indirectly related to alcohol in 1993 is greater than in previous years. Alcohol-related deaths can be viewed as a measure of the health status of the population.

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ASFR

(See Age Specific Fertility Rate.)


ASMR

Age Standardized Mortality Rate (See Age Standardization.)


AVERAGE AGE

The average age of a population is based on the estimated mid-year population (except for census data).


BIRTH ORDER

Denotes the number position of the present birth relative to previous live births. That is, whether the live birth being counted is the 1st, 2nd, 3rd, etc. live born infant to a particular mother.


BIRTH RATE

(See Crude Rates.)


BIRTH WEIGHT

The first weight of the fetus or newborn after birth. For live births this weight should be measured within the first hour of life before significant postnatal weight loss has occurred. For statistical and risk assessment purposes, birth weights are grouped as:
Extremely Low Birth Weight: weight less than 500 grams.
Very Low Birth Weight:weight less than 1500 grams.
Low Birth Weight (LBW):weight less than 2500 grams.
Normal Birth Weight:weight from 2500 to 4499 grams.
High Birth Weight: exceptionally large baby with a birth weight of 4500 grams or more.

BIRTHS

(See Total Births.)


BREECH

(See Mode of Delivery.)


CESAREAN

(See Mode of Delivery.)


COMMUNITY

A geographic area defined by a municipal (city, town, village, or district municipality) boundary. In this report, data are provided only for those communities which are incorporated.


CONFIDENCE INTERVAL

(See Statistical Test.)


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CONGENITAL ANOMALIES

Physical defects that existed or date from birth.


CRUDE RATES

  • For live births: the crude rate is the number of births divided by the mid-year population and converted to a rate per 1,000 population.
  • For birth-related statistics (teenage mother, elderly gravida, C-section, low birth weight, and pre-term): the rate is the number of these births divided by the number of live births and converted to a rate per 1,000 live births.
  • For stillbirths and perinatal deaths: the rate is the number of stillbirths, perinatal deaths divided by the number of total births (live births plus stillbirths) and converted to a rate per 1,000 total births.
  • For infant deaths: the crude rate is the number of infant deaths divided by the number of live births and converted to a rate per 1,000 live births.
  • For maternal deaths: the rate is the number of maternal deaths divided by the number of live births, and converted to a rate per 10,000 live births.
  • For deaths and mortality statistics: the crude rate is the number of deaths divided by the mid-year population and converted to a rate per 1,000 population.
  • For marriages: the crude rate is the number of marriages divided by the mid-year population and converted to a rate per 1,000 population.

DEATH RATE

(See Crude Rates.)


DEATHS DUE TO MEDICALLY TREATABLE DISEASES

Deaths due to medically treatable diseases are based on Charlton's1 classification. The disease categories (shown below) are ones for which mortality could potentially have been avoided through appropriate medical intervention. The calculation of this measure is based on deaths where the underlying cause stated on the medical certificate of death falls into one of these categories.

ICD9 Code(s) Diagnostic Category (Charlton)
001-005, 020-041, 320, 382, 383
390-392, 680-686, 711, 730		 Bacterial infections (age 5-64)
010-018, 137 Tuberculosis (age 5-64)
180 Cervical cancer (age 5-64)
201 Hodgkin's disease (age 5-34)
280, 281 Deficiency anemias (age 5-64)
393-398 Chronic rheumatic heart disease (age 5-44)
401-405 Hypertensive disease (age 5-64)
460-466, 487 Acute respiratory infections and influenza (age 5-49)
481-486, 490 Pneumonia and unspecified bronchitis (age 5-49)
493 Asthma (age 5-49)
540-543, 550-553, 574, 575 Abdominal hernias, cholecystitis, cholelithiasis and appendicitis (age 5-64).

DRUG-INDUCED DEATHS

Deaths due to drug-induced causes. This category of deaths excludes accidents, homicides, and other causes indirectly related to drug use, as well as alcohol-related deaths and smoking-attributable mortality. With the exception of codes E930-E949, the causes of death classified as being drug-induced (as shown below) are those used by the National Center for Health Statistics (National Center for Health Statistics (1993). Technical notes. Monthly Vital Statistics Report. 41 (Suppl. 7), 48). ICD9 codes 779.5 (drug withdrawal syndrome in newborn) and E929.2 (late effects of accidental poisoning) were also considered but were excluded as they could include alcohol as well as other drugs.

ICD9 Code(s) Diagnostic Category
292 Drug psychoses
304 Drug dependence
305.2-305.9 Nondependent use of drugs, not including alcohol and tobacco
E850-E858 Accidental poisoning by drugs, medicaments, and biologicals
E930-E949 Drugs, medicaments, and biologicals causing adverse effects in therapeutic use
E950.0-E950.5 Suicide by drugs, medicaments, and biologicals
E962.0 Assault from poisoning by drugs and medicaments
E980.0-E980.5 Poisoning by drugs, medicaments, and biologicals, undetermined whether accidentally or purposely inflicted

1 Charlton, J.R.H. (1987). Avoidable Deaths and Diseases as Monitors of Health Promotion. In T. Abelin, Z.J. Brzezinski, & V. Carstairs (Eds.), Measurement in Health Promotion and Protection (pp. 467-479). Copenhagen, Denmark: World Health Organization, Regional Office for Europe.

EARLY NEONATAL DEATH

Death of a child under seven days of age.


ELDERLY GRAVIDA

Any woman who was 35 years of age or older at the time of delivery of a live born infant.


EXPECTED DEATHS

The number of deaths expected for residents of a sub-provincial geographic area, based on the age-specific mortality rates for the province as a whole and the population age structure of the sub-provincial geographic area. (See Statistical Computation for an example.)


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EXPECTED LOW BIRTH WEIGHT

The number of expected low birth weight live births to residents of a sub-provincial geographic area based on low birth weight rates for the province as a whole and the number of births in the sub-provincial geographic area. (See Statistical Computation under Low Birth Weight (LBW) Live Births for an example.)


EXPECTED POTENTIAL YEARS OF LIFE LOST

The number of potential years of life lost (to age 75, as in this report) expected for residents of a sub-provincial geographic area based on the age-specific mortality rates for the province as a whole and the population age structure of the sub-provincial geographic area. (See Statistical Computation under Potential Years of Life Lost Index for an example.)


FERTILITY RATE

The number of live births occurring in a given time period divided by the number of women of child-bearing age for residents of a geographic area. B.C. rates are per 1,000 women aged 15 to 44. Canadian rates are per 1,000 women aged 15 to 49. (See Total Fertility Rate.)


FORCEPS OR SUCTION

(See Mode of Delivery.)


GESTATIONAL AGE

Fetal age or duration of pregnancy measured from the first day of the last normal menstrual period. Gestational age is expressed in completed days or completed weeks (e.g., events occurring 280 to 286 days after the onset of the last normal menstrual period are considered to have occurred at 40 weeks of gestation).

Measurements of fetal growth, as they represent continuous variables, are expressed in relation to a specific week of gestational age as follows:

  • Extremely premature: gestational age of less than 28 weeks.
  • Moderately premature: gestational age of 28 to 36 weeks.
  • Pre-term/Premature: age less than 37 weeks of gestation.
  • Term: gestational age of 37 to 41 weeks.
  • Post-term/Postmature: gestational age of 42 weeks or more.

HEALTH REGION (HR)

A geographic subdivision of the province used by the Ministry of Health for data dissemination purposes. In 1994, the Ministry began an extensive regionalization process which established Regional Health Boards, Community Health Service Societies, and Community Health Councils. This publication includes data by 20 health regions (HR); beginning with this 1998 report, the boundaries of these HR have been revised to correspond to those of the revised local health areas. To ensure data is provided for all the regional health authorities, additional data for Vancouver/Richmond Regional Health Board and the Simon Fraser Health Board have been included in Appendix 3.

Figure 2 presents a map of the province by health region.


HIV

(See Human Immunodeficiency Virus.)


HUMAN IMMUNODEFICIENCY VIRUS (HIV)

The virus that causes acquired immunodeficiency syndrome (AIDS).


ICD9 CODES

International Classification of Diseases Codes, Ninth Revision, established by the World Health Organization (1977).


INFANT MORTALITY

Death of children under one year of age.


INFANT MORTALITY RATE

The number of deaths of children under one year of age expressed as a rate per 1,000 live births. The infant mortality rate is an internationally accepted indicator of the health status of a population.


LBW

(See Low Birth Weight.)


LHA

(See Local Health Area.)


LIFE EXPECTANCY

Life expectancy at age 0 represents the mean number of years a birth cohort (persons born in the same year) may expect to live given the present mortality experience of a population. The life expectancy for a population is a summary measure that reflects the mortality rates for all ages combined, weighted in accordance with a life-table population structure. Life expectancy is an internationally accepted indicator of the health status of a population.


LIVE BIRTH

The complete expulsion or extraction from its mother, irrespective of the duration of the pregnancy, of a product of conception in which, after the expulsion or extraction, there is:
    (a) breathing;
    (b) beating of the heart;
    (c) pulsation of the umbilical cord; or
    (d) unmistakable movement of voluntary muscle, whether or not the umbilical cord has been cut or the placenta attached.

LOCAL HEALTH AREA (LHA)

A geographic subdivision of the province used by the Ministry of Health for data dissemination purposes, which can be aggregated into health regions (HR). In 1994, the Ministry began an extensive regionalization process that established Regional Health Boards, Community Health Service Societies, and Community Health Councils. Some of the boundaries of these new health authorities were adjusted in the regionalization process, resulting in significant revisions to the LHA boundaries. Beginning with this 1998 report, regional data and maps use the revised LHA boundaries that correspond to, or can be aggregated to, the boundaries of the regional health authorities. In LHA tables, four pairs of LHAs have been merged into combined areas for data dissemination purposes, to have their boundaries correspond to those of Community Health Councils. Because of these changes, the data for many of the LHAs cannot be compared to data published in previous reports.

Figure 1 presents a map of the province by local health area (LHA).


LOW BIRTH WEIGHT (LBW)

A birth weight of less than 2,500 grams. Low birth weight babies have increased risks of morbidity and premature death.


LOW BIRTH WEIGHT RATE

The number of low birth weight live born babies per 1,000 live births.


MARRIAGE RATE

(See Crude Rates.)


MATERNAL DEATH/MORTALITY

A maternal death is the death of a woman while pregnant or within 42 days of termination of pregnancy, irrespective of the duration or the site of the pregnancy, from any cause related to or aggravated by the pregnancy or its management (direct or indirect obstetrical) but not from accidental or incidental causes.


MATERNAL MORTALITY RATE

Maternal deaths expressed as a rate per 10,000 live births.


MID-YEAR POPULATION

The estimated (except for census data) population at the midpoint of the year, which approximates the average population for the year.
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MODE OF DELIVERY

  • Spontaneous: An unassisted (spontaneous) delivery of a fetus.
  • Forceps or Suction: An assisted delivery employing forceps or vacuum.
  • Breech: A spontaneous or assisted delivery in which the buttocks or feet of the fetus appear first.
  • Cesarean: A delivery involving the surgical incision of the abdomen and uterine walls.

MVA DEATHS

Motor Vehicle Accidental Deaths (ICD9 codes: E800-E825).


NATURAL POPULATION INCREASE

The component increase in a population due to the number of live births less deaths. This increase may often be expressed as a rate, such as per 1,000 population.


NEONATAL DEATH

Death of a child under 28 days of age.

OBSERVED DEATHS

The actual number of deaths that occurred in the province to residents of a geographic area in a specified time period.


OBSERVED LOW BIRTH WEIGHT LIVE BIRTHS

The actual number of low birth weight live births that occurred in the province to residents of a geographic area in a specified time period.


OBSERVED PYLL

The actual number of potential years of life lost (to age 75) from deaths that occurred in the province to residents of a geographic area in a specified time period.


OUT-OF-WEDLOCK BIRTHS

Births where the mother of the baby is not lawfully married to the father of the baby.


P-VALUE

(See Statistical Test.)

PERINATAL

Pertaining to or occurring in the period shortly before, during, and after birth.


POPULATION

Mid-year populations (estimates, except for census data) for the province were obtained from Statistics Canada. Population estimates for Health Regions, Local Health Areas, and Communities were provided by BC STATS, Ministry of Government Services. These estimates are based upon census data and data regarding births, deaths, migration, and other factors. (See Standard Population.)


POST NEONATAL DEATH

Death of a child between the ages of 28 days and less than one year.


POST-TERM

(See Gestational Age.)


POTENTIAL YEARS OF LIFE LOST (PYLL)

The number of years of life lost when a person dies before a specified age (e.g., 75 years). In this report, all deaths are assumed to occur at the midpoint of five-year age groups. (See Statistical Computation for an example.)


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PRE-TERM

(See Gestational Age.)


PYLL INDEX (PYLLI)

The ratio of an area's observed PYLL to its expected PYLL. This is a health status indicator. (See Statistical Computation for an example.)


PYLL STANDARDIZED RATE (PYLLSR)

An age-standardized measure of an area's PYLL, expressed in terms of a rate per 1,000 population, adjusted to a standard population (1971 Canada Census). This is a health status indicator. (See Statistical Computation for an example.)


PYLLI

(See PYLL Index.)


PYLLSR

(See PYLL Standardized Rate.)


QUINTILE

A ranking is derived by dividing a group (e.g., LHAs within British Columbia) into five subgroups, each with equal numbers of LHAs. These divisions are derived from a ranking of the group members according to the value of a measure, such as the SMR or the PYLLI.


SAM

(See Smoking-attributable Mortality.)


SAM(%)

(See Smoking-attributable Mortality.)


SIDS

Sudden Infant Death Syndrome.


SMOKING-ATTRIBUTABLE MORTALITY (SAM)

The absence on death certifications of complete and reliable data on smoking as a contributing factor requires that estimation or other techniques be used to approximate the extent of smoking-attributable deaths. Estimation methods, while not precise, may at least provide a general indication of the extent of such deaths. The method used here is based on the concept of attributable risk.

To define attributable risk mathematically, consider d0 and d1 respectively to represent the death rates, in a given time period, in two cohorts from a population - those not exposed and those exposed to a given risk factor. The attributable risk of this factor, AR1 , would then be:

Image

Where:

    r1 = d1/d0 is the relative risk of the exposed cohort.
    The relative risk of the unexposed cohort is r0 = 1; the attributable risk of this cohort is AR0 = 0.
    The attributable risk (AR) for the population as a whole (exposed plus unexposed cohorts) is given by:

Image

Where:
    p1 = the proportion or fraction of the population exposed to the risk factor; and
    1-p1 = the proportion or fraction of the population not exposed to the risk factor.
This may be extended to account for multiple levels of exposure as follows:

Image

Where:
    pi = the proportion (prevalence) of the population in the ith level of exposure group;
    ri = the relative risk at the ith level of exposure; and
    i = the ith risk category
    .
When applied to smoking-attributable mortality (SAM), the attributable risk is often expressed as a percentage:

SAM (%) = AR x 100

The number of adult (35+ years of age) smoking deaths in British Columbia were estimated for 19 diseases. Smoking-attributable deaths are derived by multiplying the smoking-attributable mortality percentage expressed as a decimal fraction by the number of deaths in each diagnostic category listed below.

ICD9 Code(s)Diagnostic Category
140-149 Malignant neoplasms of lip, oral cavity, and pharynx
150 Malignant neoplasm of esophagus
157 Malignant neoplasm of pancreas
161 Malignant neoplasm of larynx
162 Malignant neoplasm of trachea, lung, and bronchus
180 Malignant neoplasm of cervix uteri
188 Malignant neoplasm of urinary bladder
189 Malignant neoplasm of kidney and other urinary organs
401-404 Hypertension
410-414 Ischaemic heart disease
415-417, 420-429, 390-398 Other heart diseases
430-438 Cerebrovascular disease
440 Atherosclerosis
441 Aortic aneurysm
442-448 Other arterial disease
480-487 Pneumonia and influenza
491-492 Bronchitis and emphysema
493, 010-012 Other respiratory diseases
496 Chronic obstructive pulmonary disease

Relative-risk data from the American Society's Cancer Prevention Study (CPS) II (1982-1988) (Centers for Disease Control, 1990) were selected for use, as they have been widely used for similar analyses. The data from the CPS-II established the age groups and the classification of smokers (current, former, and never) for which smoking prevalence data were required. The relative risk age categories were for 35+, or 35-64 and 65+. For the Vital Statistics Annual Reports up to 1996, the available smoking prevalence data were available for the broader age group 25-44; therefore the assumption had to be made that the prevalence rates for age groups 35+ were the same as the rates for age groups 25+. Additionally, provincial prevalence age group rates were not published, and had to be approximated by adjusting the Canadian rates.

Beginning with the 1997 Annual Report, actual B.C. prevalence rates were available separately for the required 25-34 and 35-44 age categories from the Tobacco Use in BC (1997) survey commissioned by the BC and Yukon Health and Stroke Foundation2. These additional prevalence data enabled the SAM% to better reflect B.C. data. As a result of this change, comparisons should not be made to earlier estimates of smoking attributable mortality.

Reference

Centres for Disease Control (1990). Smoking and health: A national status report. (DHSS publication no. (CDC) 87-8396). 2nd Edition. Rockville, MD: U.S. Department of Health and Human Services.

2 Detailed information from the Tobacco Use in BC (1997) survey is on CD-ROM. A link to summary data can be found on the ministry's web page http://www.hlth.gov.bc.ca/program.html

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SMR

(See Standardized Mortality Ratio.)


SPONTANEOUS DELIVERY

(See Mode of Delivery.)


STANDARD POPULATION

A reference population of known age distribution used in the calculation of standardized indicators to adjust for variations in population age structures in different geographic areas or time periods. For SMR and PYLLI calculations the standard population is the British Columbia population for the year(s) concerned. Beginning in this 1998 report, the 1991 Canadian Census is used as the standard population in the calculation of ASMR and PYLLSR, replacing the 1971 Male and Female Census populations used in previous reports. Because of this update, ASMR and PYLLSR in this publication cannot be compared to those previously published by the Agency.


STANDARDIZED MORTALITY RATIO (SMR)

The ratio of the number of deaths occurring to residents of a geographic area (e.g., LHA) to the expected number of deaths in that area based on provincial age-specific mortality rates. The SMR is a good measure for comparing mortality data that are based on a small number of cases or for readily comparing mortality data by geographical area. SMR is an internationally recognized health status indicator. (See Age Standardization and Standard Population ; for an example see Statistical Computation.)


STATISTICAL COMPUTATION

The following provides the reader with computational examples of how various measures are calculated. In the examples, LHAs have been employed as the geographic unit of analysis.
  • Age Standardized Mortality Rate (ASMR):


LHA
AgeStandardEstimatedDeath Observed
GroupPopulationPopulationRate/10,000 Deaths
(i)Image(pi)(mi)(di)
< 1355,8701,33922.43
1-41,460,2855,4831.81
.....
.....
.....
80-84204,1701,198701.284
85 +137,3909081596.9 145
TOTAL21,568,31581,016 561

For the Local Health Area:

Image


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  • Fertility Rate:

LHA
AgeLiveFemaleAge Specific
GroupBirthsPopulationFertility Rate
(i)(bi)(wi)(ASFRi)
15-191959831.8
20-2446440104.5
25-2974498148.6
30-345174568.5
35-391269017.4
40-4425813.4
TOTAL2043,552374.2

For the Local Health Area:

  1. the age-specific fertility rate (ASFR) for age group 15-19 years is:

    ASFRi=bi/wi x 1,000 = 19/598 x 1,000=31.8

    Where:
    bi = number of live births for age group i; and
    wi = number of female population for age group i.

  2. the total fertility rate (TFR)is:

    Image


    Where:
    ASFRi = age specific fertility rate for age group i; and
    a = number of years in each age group i.
  • Low Birth Weight (LBW) Live Births:

LHABritish Columbia
Low Birth WeightLow Birth Weight
Live BirthsTotalLive BirthsTotal
YearObservedExpectedLive BirthsObservedLive Births
(i)(Oi)(Ei)(Li ) (bi)(Bi)
19859282.91,7012,09642,989
19866974.61,5881,96541,846
198710280.21,5822,11341,655
19888574.71,4952,14542,913
19899178.11,5012,26743,586
TOTAL439390.67,86710,586212,989


For the Local Health Area:

  1. the expected low birth weight live births for year i = 1985 were:

    Image

    Where:
    bi = number of LBW live births for the province in year i;
    Bi = number of live births for the province in year i; and
    Li = number of live births for the LHA.
  2. the ratio of observed over the expected LBW live births for the five-year peroid was:

    Image

    Where:
    Oi = observed LBW live births for year i; and
    Ei = expected LBW live births for year i.
  3. Chi-Square (X2):
Image

  • Potential Years of Life Lost (PYLL) and Standard Rate (PYLLSR):

LHA
AgeAgeStandardEstimatedDeathObservedObserved
GroupFactorPopulationPopulation Rate/1,000DeathPYLL
(i)(75-Yi)Image(pi)(mi)(di)(di(75-Yi))
< 174.5355,8701,3392.23223.5
1-472.01,460,2855,4830.2172.0
5-967.52,254,0056,5530.2167.5
.......
.......
.......
65-697.5619,9553,53818.766495.0
70-742.5457,3802,77928.880200.0
TOTAL-21,568,31579,1402393,183.0

For the Local Health Area:

Image


Image


Image


  • Potential Years of Life Lost Index (PYLLI):


Image

For the Local Health Area:

Image


Where:
O = observed PYLL;
E = expected PYLL;
di = observed deaths in age group i;
ei = expected deaths in age group i;
Yi = age at midpoint of age group i;
pi = LHA population for age group i;
Pi = provincial population for age group i;
Di = provincial deaths for age group i; and
mi =(di/pi) x 1,000 = mortality rate per 1,000 LHA population in age group i.

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  • Standardized Mortality Ratio (SMR):

LHABritish Columbia
AgeEstimatedDeathObservedExpectedEstimatedDeathObserved
GroupPopulationRate/1,000DeathsDeathsPopulationRate/1,000Deaths
(i)(pi)(mi)(di)(ei)(Pi)(Mi)(Di)
< 11,3392.2310.342,7007.7328
1-45,4830.211.9172,5000.461
........
........
........
80-841,19870.18487.248,10072.83,502
85+908159.7145138.834,500152.85,272
TOTAL81,016561595.13,131,70023,389


For the Local Health Area:

Image


Where:
    di = observed deaths in age group i; and
    ei = expected deaths in age group i
1) Observed Deaths (d)
The actual number of deaths that occurred in the LHA. For example, for age group under one year of age, the observed deaths are three.

2) Expected Deaths (e)
The number of deaths expected for residents of the LHA based on the age specific mortality rates for the province as a whole and the population age structure of the LHA. For age group under one year, the expected deaths are:

Image


Where:
    pi = LHA population for age group i;
    Di = provincial death for age group i; and
    Pi = provincial population for age group i.

STATISTICAL TEST

  • P-VALUE
The p-value is the probability of rejecting the null hypothesis when a specified test procedure is used on a given data set. This probability is the smallest level of significance at which the null hypothesis would be rejected. Once the p-value has been determined, the conclusion at any particular level a results from comparing the p-value to a (e.g., 0.05):
(a) p-value less than or equal to a reject null hypothesis at level a,
(b) p-value >  a do not reject the null hypothesis at level a,
and we call the data statistically significant when the null hypothesis is rejected and not significant otherwise.

  • For rates, such as ASMRs, the test employed to determine statistical significance is a confidence interval. The 95% confidence interval for the difference (D) between a LHA and a provincial rate is defined by the upper and lower limits of the interval as follows:
Image


Image


Where:
    Rl = Rate for LHA l;
    Rp = Rate for the province;
    Ol = Observed number for LHA l; and
    Op = Observed number for the province.
If the Lower Limit > 0, then Rl is statistically significantly higher than Rp;
if the Upper Limit < 0, then Rl is statistically significantly lower than Rp; otherwise,
there is no statistically significant difference.

  • For ratios, such as SMRs, a Chi-square (X 2) test is applied to determine whether the observed number of cases is statistically significantly different from the expected number. For LHA l:
Image

  • For SMR values, the Chi-square statistic that is applied is:
Image

Where:
    Ôl = Ol if Ol>  El; otherwise
    Ôl = Ol + 1

STILLBIRTH

The complete expulsion or extraction from its mother after at least 20 weeks of pregnancy, or after attaining a weight of at least 500 grams, of a product of conception in which, after the expulsion or extraction, there is no breathing, beating of the heart, pulsation of the umbilical cord, or unmistakable movement of voluntary muscle.

The definition of a stillbirth has changed over the years. From July 1, 1962 until January 1, 1986, the definition of a stillbirth did not include the phrase "or after attaining a weight of at least 500 grams. " For the earlier years shown in this report, prior to July 1, 1962, the definition of a stillbirth was: the birth of a viable fetus after at least 28 weeks pregnancy in which pulmonary respiration does not occur, whether death occurs before, during, or after birth.


STILLBIRTH RATE

(See Crude Rates.)


TERM

(See Gestational Age.)


TFR

(See Total Fertility Rate.)


TOTAL BIRTHS

The number of live births plus stillbirths.


TOTAL FERTILITY RATE (TFR)

The rate is calculated by summing all of the age-specific birth rates multiplied by the number of years by which the age-specific birth rates are grouped (this assumes the same number of women in each age group). "The total fertility rate indicates the number of births that a group of 1,000 women would have if they experienced, during their childbearing years (i.e., age 15 to 44 years), the age-specific birth rates observed in a given calendar year. It is a hypothetical measure that shows the implications of current levels of fertility by age for completed family size." (National Center for Health Statistics. Supplements to the monthly vital statistics report: advance reports, 1987. National Center for Health Statistics. Vital Health Stat 24 (4) p. 5. 1990.) (See Statistical Computation for an example.)


TOTAL PYLL

The total number of years of life lost prior to an established cut-off point of 75 years.


TREND ANALYSIS OF ASMR

Appendix 3 presents summaries of various health status indicators by local health area and health region. In order to identify significant trends in ASMRs in the 1985 to 1998 period, this Annual Report used a statistical technique called linear regression. The use of the linear regression model was not intended for predictive purposes; rather the methodology was intended only to provide a description of the ASMRs over the time period.

Data for individual years contain a certain amount of stochastic variability; especially when data consist of small numbers, the stochastic variability can reduce the reliability of using a linear regression model to describe time series data. In order to dampen the effects of stochastic variability in the ASMRs, a three-year moving average process was applied to create 12 smoothed data points for years 1985 to 1998 (i.e., the moving averages were calculated for the periods 1985 to 1987, 1986 to 1988, ... , 1996 to 1998). A linear regression was then calculated in the form:

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The slope of this regression line was tested at the 5% level and the trend was described as follows:

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Trends were not shown for areas with an average of less than 1 death per year in the 14-year period, 1985 to 1998.


VERY LOW BIRTH WEIGHT

A birth weight of less than 1,500 grams.


UCOD

(See Underlying Cause of Death)


UNDERLYING CAUSE OF DEATH (UCOD)

The underlying cause of death is the disease which triggered the chain of events leading directly to the death or the description of the accident or violence that produced the fatality (World Health Organization, 1977).