Morbidity-data sources and measures

Farid NajafiMD PhD

Kermanshah Health Research Center (KHRC)Kermanshah University of Medical Sciences

Question

References

What are we measuring?

Criteria for diagnosis is the first step (case fefinition)Different case definition leads to different values

Prevalence

Prevalence rate is a wrong expressionIt is a simple proportion or percentage

Period prevalence: it requires a smaller survey sample to find enough casesFor an accurate estimate.“Did your child have diarrhea during any of the last 7 days?

Incidence

• Incidence measures how quickly people are developing a disease

• Population at risk:– Cervical cancer

• Women vs. men• Women after hysterectomy

Relationship between incidence and prevalence

• Direct relationship between incidence and prevalence

P=I*D– Hepatitis A vs. Hep C

• To measure the prevalence we need to conduct a cross-sectional study

• To measure the incidence we need to conduct a follow-up study

Incidence rate versus cumulative incidence

• IR is equivalent to the average speed of a car at a particular point in time, e.g. 60 km/hour

• CI is analogous to the distance travelled by a car during a specified interval of time, e.g. 60 Km in one hour

Measuring disease occurrence using routine data

• Most of our information come from routine data

• Data are not individual base

• No causal association between disease and other factors

• We are usually interested in incidence

• Difference between crude, age-specific and stadardised incidence and prevalence

Raw health data

• Data can be assessed at two levels1. Summary data

2. Raw counts of health events

• More challenge about morbidity data compared to mortality data

– Capturing in a less systematic way– Scope of information is enormous– No complete informatin at a local level

Disease registeries

• It covers only small minority of conditions– CHD: first studied in MONICA Project in the

early 1980s– Cancer: Most countries, most notably in

Scandinavia, have cancer registries that cover the whole country

• Cancer is an ideal candidate for registration because of its clear-cut diagnosis, based on a single simple record (pathology)

– Many infectious diseases

Health Surveys

• There are two major challenges– Representativeness: sample has been

chosen to be representative of whole population

• No inclusion of homeless people• Those who disagree to participate (response rate)

– Validity; the extent to which a survey actually measures what it set out to measure

Validity

Health facility data

• Hospital records: usually based on discharge diagnosis as recorded and coded on the patient’s record with varying degreees on misdiagnosis, mis-recording and mis-coding– Not representing the general population

• For fatal and serious conditions, hospital records provide useful information

• Lack of unique patients identifier• No information about condition treated by family practioners

or n home

Getting access to the data

• International sources– World Health Organization (http://www.who.int

)– World Bank (http://www.worldbank.org)– National data sources

• Ministry of Health