Epidemiological Variables and Sources of Data

Slide 1 Epidemiological variables Sources of data Cor Jonker Slide 2 Contents Rate, Ratio, Proportion Incidence, Prevalence Births Morbidity...

Slide 1 Epidemiological variables Sources of data Cor Jonker Slide 2 Contents Rate, Ratio, Proportion Incidence, Prevalence Births Morbidity Mortality Sources of information Slide 3 Rate, Proportion, Ratio Rate: measure of frequency of an event in a population over time Proportion: part of a population affected Ratio: rate or proportion in one population compared to that of another population All three are calculated as a fraction: Slide 4 Rate -- Incidence Incidence rate: frequency of new cases of a disease in a population over time. Expressed per standard size of population Easy to compare populations Example: Age-standardized incidence rate of cervical cancer (ASIR cervical cancer) The ambition of WHO is to reduce the ASIR of cervical cancer to less than 4 per 100 000 women worldwide by vaccinating 90% of all girls by age 15 years, screening 70% of women twice in the age range of 35–45 years, and treating at least 90% of all precancerous lesions detected during screening. Slide 5 ASIR per sub-continent (per 100,000 women) WORLD 13.1 Northern 6.4 Australia and 6.0 America New Zealand Eastern Africa 40.1 Eastern Asia 10.9 Melanesia 27.7 Middle Africa 26.8 South-eastern 17.2 Micronesia 18.6 Asia Northern Africa 7.2 South-central 13.0 Polynesia 10.7 Asia Southern Africa 43.1 Western Asia 4.1 Western Africa 29.6 Central-eastern 16.0 Europe Caribbean 15.5 Northern Europe 9.5 ASIR 2018 data Cervical Cancer Central America 13.0 Southern Europe 7.8 South America 15.2 Western Europe 6.8 Source: Arbyn, et al (2020) Slide 6 Proportion -- Prevalence Proportion = comparison of a part to the whole Expressed as a percentage or a fraction or a decimal Example: Prevalence of diabetes in the population Warning: sometimes called ‘rate’ Slide 7 COUNTRY PREVALENCE NUMBER OF PEOPLE Prevalence England 5.1% 2,213,138 of diabetes (T1DM & Northern 4.5% 65,066 Ireland T2DM, 2009) Wales 4.6% 146,173 Scotland 3.9% 209,886 Slide 8 Ratio Ratio = relative magnitude of two quantities or a comparison of any two values Often expressed as ‘…to one’. Slide 9 Death-to-Case Ratio Death-to-case ratio is the number of deaths attributed to a particular disease during a specified period divided by the number of new cases of that disease identified during the same period. Expressed as a proportion out of 1 or as a percentage. Slide 10 Covid-19 Case-Fatality Ratio Source: Johns Hopkins University, Coronavirus Resource Center Slide 11 Covid-19 Death Rate per 100,000 population Source: Johns Hopkins University, Coronvirus Resource Center Slide 12 Source: Bophal & Bophal, 2020 Risk Ratios for Covid-19 England & Wales, France, Germany, Italy, Netherlands, Portugal, Korea and Spain Population Deaths Age group Male Female Male Female Sex Ratio M:F 0-9 19923780 18935073 6 7 0.81 10-19 21333098 20087329 14 9 1.46 20-29 23719884 22435304 94 50 1.78 30-39 25310993 25157644 282 170 1.65 40-49 27912903 27945866 993 531 1.87 50-59 29327752 29834735 3776 1661 2.31 60-69 22611177 24271853 9590 4024 2.56 70-79 15668774 18552985 21830 10940 2.36 80+ 8541230 14494575 41067 42199 1.65 ALL 194349591 201715364 77652 59591 1.35 Slide 13 Demographic descriptors Demographic descriptors are important to provide baseline information on the population in an area To estimate current health care needs and whether these are currently met To estimate future health care needs To respond in case of a medical emergency (outbreak, natural disaster, etc.). Slide 14 Useful for comparing different sub-populations Useful for calculating At-Risk Age-Sex population size Breakdown Useful for understanding (and planning ahead) the health care needs of the population, for instance by analysing a population pyramid. Slide 15 Slide 16 Slide 17 Country Population per Population KM2 density United Kingdom 275 Germany 240 Population density: average number of persons France 122 per square km An increase in the density shows inward Greece 81 migration Useful for calculating Turkey 110 health care needs of the population now and in the future India 382 Slide 18 Age-sex data and population density are based on population censuses. Census These are reliable in some countries and unreliable in others. Some countries have replaced them with surveys on samples. Slide 19 Demographic indicators Crude birth rate: High fertility: CBR 45 per 1000 per year Low fertility: CBR 20 per 1000 per year CBR changes allow you to make predictions for maternal service requirements in the future Slide 20 Fertility rates Total Fertility Rate = average number of children that would be born to a woman over her lifetime if she would live her entire fertile life and would have the exact calculated age-specific fertility rates of the population (this is an artificial rate). Slide 21 TFR = 2.0 or thereabout would mean that the population is stable (no growth or decrease). A better estimate would be the Net Reproduction Rate (NRR) NRR = Similar to TFR but based on baby girls born only and on age-specific birth rates AND age-specific mortality rates for the virtual woman of the population. NRR = 1 would mean zero population growth or decline Slide 22 Crude Death Rate High income areas: CDR = 10 per 1000 per year Low income areas: CDR = 20 per 1000 per year Slide 23 Infant Mortality Rate Infant = liveborn child < 12 months IMR = good measure of health status of community IMR = rarely accurate unless there is a good vital registration available Low income countries: IMR = 60 to 150 per 1000 births per year High income countries: IMR = 5 to 10 per 1000 births per year Neonatal mortality Rate: same calculation but for liveborn children < 1 month Child Mortality Rate: deaths of children between 1 and 4 years of age (important for malnutrition and infectious diseases) Slide 24 Maternal Mortality Rate (MMR) Factor = 1000 or 10 000 or 100 000 Low income countries: MMR = 100 to 1000 per 100 000 per year High income countries: MMR = 1 to 15 per 100 000 The chance of dying from child birth also depends on the average number of children per woman in that area Slide 25 Population growth: Births + inward migration – deaths – outward migration Rate of natural increase: CBR – CDR Slide 26 Census data Population registers Sources of Local studies information Office of National Statistics surveys Setting up own survey Slide 27 Where to find statistics UK statistics European statistics World statistics https://rl.talis.com/3/bradford/lists/A5DB24F9-0DA5-D78E-FB48- BA4CA08D1920.html