This document provides definitions and explanations of various medical statistics used to analyze health data: - General fertility rate measures births per 1000 women aged 15-44. - Crude birth rate measures births per 1000 total population. - Perinatal mortality rate measures stillbirths and infant deaths under 1 week per 1000 total births. - Infant mortality rate measures deaths of infants under 1 year per 1000 live births. - Standardized mortality ratio compares the death rate in a population to a standard population to account for age differences.

1. Medical
Statistics
PUP 4001
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2. Demographics
– http://www.indexmundi.com/united_kingdom/demographics_profile.html
– What is health care statistics?
Health statistics are numbers about some aspect of health. Statistics
about births, deaths, marriages, and divorces are sometimes called
"vital statistics." Researchers use statistics to see patterns of diseases
in groups of people.
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3. General Fertility
GFR
GFR=Number of Birth
Number of women aged 15-44 X
1000
A few births may occur to women outside
these ages
IVF!!!
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4. Birth Rate (per thousand)
Crude Birth Rate=
Number of births that year
Total population that year X 1000
(total population includes men, women and
children)
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5. Perinatal Mortality Rate-
PNMR
Per thousand
Perinatal deaths are :- (stillbirths; foetal deaths
after the 28th week of pregnancy and deaths
under 1 week post natal)
PNMR= Number of perinatal deaths
Number of live and stillbirths X 1000
(Used as a measure of safety and efficiency of
maternity services)
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6. Infant Mortality Rate-IMR
(used as a key indicator of health status
within societies)
IMR= Deaths of infants under 1 year
Number of live births X 1000
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7. Infant Mortality Rate 2010
4.6 per 1000 births
http://www.google.co.uk/publicdata/explore?ds=d5bnc
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8. Crude Death Rates
 CDR= Number of Deaths
 Total population x 1000
 (not very useful)
 (other factors such as age have to be
considered)
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9. Standardised Mortality
Ratio SMR
 Population A relative to a standard
population. This would be done by
calculating the age specific death rates
for the standard population and
comparing them with those ages in
population A.
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10. Incidence Rate
Of a disease over a period of time
Incidence=
Number of New cases over the period
Population at Risk
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11. Prevalence Rate
Of a disease at a point in time
Prevalence Rate=
Total number of cases at that time
Population at Risk
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12. SMR
SMR= Number of Deaths in Population A
Sum for all age groups of population
in age group x in population A
X
Age specific death rate for this group
in standard population
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13. SMR
 Measures the death rate taking into
account differences in age structure. The
death rate of a selected population at a
given time is taken as the baseline and
death rates for specific age bands are
calculated.
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14. SMR
 Some tables of results include the numbers of deaths for each area in a
given time- period. The numbers of deaths by themselves though do not
provide information which would allow the mortality of a particular area
to be measured for comparison purposes. To provide this information,
the population of each area is also needed in order to calculate a
mortality rate. The simplest form of mortality rate divides the total
number of deaths for an area by the population of that area. These
crude rates can however be misleading as the age structures of
populations can differ widely. This is especially true at ward-level where
some areas may have a very young age structure and others may have
a population which is predominately elderly. As mortality rates generally
increase with age the crude death rates of the latter type of area could
be expected to be worse than an area with a younger population
structure.
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15. SMR
 Some tables of results include the numbers of deaths for each area in a
given time- period. The numbers of deaths by themselves though do not
provide information which would allow the mortality of a particular area
to be measured for comparison purposes. To provide this information,
the population of each area is also needed in order to calculate a
mortality rate. The simplest form of mortality rate divides the total
number of deaths for an area by the population of that area. These
crude rates can however be misleading as the age structures of
populations can differ widely. This is especially true at ward-level where
some areas may have a very young age structure and others may have
a population which is predominately elderly. As mortality rates generally
increase with age the crude death rates of the latter type of area could
be expected to be worse than an area with a younger population
structure.
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16. SMR
SMR = Observed x 100
Expected
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17. SMR: Naidoo and Wills 95
 The SMR for any subsequent year is then the
number of deaths actually occuring as a % of the
deaths which would have been expected to occur
 if the population’s age-specific mortality
experience had remained at it’s baseline level.
 The SMR is therefore an attempt to measure the
underlying trend of death rates.
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18. Why bother?
Monitoring and surveillance of health and disease
Finding causes of disease or factors associated with early death or
disease
Detecting disease
Preventing early death or disease
Evaluating treatments
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19. Further Reading
How to read a paper: Statistics for the non-statistician. I:
Different types of data need different statistical tests
BMJ 1997; 315 doi: 10.1136/bmj.315.7104.364
(Published 9 August 1997)
Cite this as: BMJ 1997;315:364
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