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INTRODUCTION TO HEALTH STATISTICS

by Dr PHUA Kai Lit
School of Medicine and Health Sciences
Monash University Sunway Campus
Bandar Sunway, Malaysia


MORTALITY INDICATORS

Mortality = deaths

1. Infant Mortality Rate
(Deaths of infants under age 1/Total live births) X 1000

IMR = neonatal mortality rate + postneonatal mortality rate

1b. Neonatal Mortality Rate
(Deaths of infants under 28 days/Total live births) X 1000

Neonatal deaths are strongly related to congenital abnormalities

1c. Postneonatal Mortality Rate
(Deaths of infants between 28 days and 1 year old/Total live births) X 1,000

Postneonatal deaths are strongly related to environmental factors e.g. malnutrition, polluted water, contaminated food etc.

1d. Toddler Mortality Rate
(Deaths of children aged 1-4/Total live births) X 1,000

2. Maternal Mortality Rate
(Number of maternal deaths/Total live births) X 100,000

3. Crude Death Rate
(Total deaths/Total population) X 1,000

Note that this is NOT a good indicator because it is affected by the age composition of the population.

3b. Age-specific Death Rate
Example: The age-specific death rate for age group 25-35 is:

(Deaths of people aged 25-35/Total pop. aged 25-35) X 1,000

Age-specific death rates are highest for the 0-5 year age group and the 65-80 age group.

3c. Age-standardized Mortality Rate (Age-adjusted Mortality Rate)

Used to compare death rates from two populations with very different age compositions.

a. Choose a "standard population"
b. Calculate the two standardized mortality rates
c. Compare the two standardized mortality rates

What we have done here is to transform two populations with different age compositions so as to make them comparable, i.e., we are saying "Assume both Population A and Population B have the age composition of the 'standard population', what then would be their respective mortality rates?"

4. Cause-specific Death Rate
(Number of cancer deaths/Total population) X 100,000

5. Life Expectancy
a. Life expectancy at birth
b. Life expectancy at age X

Calculation of life expectancy is based on the age-specific death rates for a particular year.

MORBIDITY INDICATORS

Morbidity = sickess

1. Prevalence Rate (point prevalence)
(No. of persons with a specific disease/Total pop. at risk) X 1,000

2. Incidence Rate
(No. of new cases of a disease within a given time period/Pop. at risk) X 1,000

TRENDS

Whenever possible, data should be graphed to look for patterns.
Trends may include: declining trend, increasing trend, fluctuating trend and so on.

CYCLES (Periodicity)

Sometimes, cases of disease occur in cycles. Some diseases increase during particular seasons e.g. GI diseases increase during monsoon seasons since floods increase the risk of contamination of water supply. In the USA, influenza cases increase during the winter months because people tend to crowd together indoors and so on.

EVIDENCE-BASED MEDICINE

You may be surprised to hear that some commonly used drugs, medical procedures and practices are shown to be ineffective when subjected to rigourous, clinical trials. But doctors continue to use these. Why?

1. They learned these in medical school
2. Their professors practise medicine this way
3. Some doctors never keep track of the latest medical advances
after graduating from medical school
4. Resistance to change ("old habits die hard")

Evidence-based medicine is meant to investigate which drugs, medical procedures etc. are effective and which are not (or even dangerous). Randomized controlled clinical trials (RCT) are an important tool in research to promote evidence-based medicine.

Aims of Evidence-based Medicine

Subject medical technology to rigorous clinical trials
Eliminate ineffective or even dangerous technology
Reduce iatrogenic sickness
Reduce unnecessary economic costs
Produce clinical practice guidelines

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