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Population Surveys Methodologic problems: standardization

Population Surveys Methodologic problems: standardization. Maura Pugliatti, MD, PhD Associate Professor of Neurology Dept. of Clinical and Experimental Medicine, Unit of Clinical Neurology University of Sassari, Italy 1 st International Course of Neuroepidemiology

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Population Surveys Methodologic problems: standardization

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  1. Population Surveys Methodologic problems: standardization Maura Pugliatti, MD, PhDAssociate Professor of NeurologyDept. of Clinical and Experimental Medicine, Unit of Clinical NeurologyUniversity of Sassari, Italy 1st International Course of Neuroepidemiology Chisinau, Moldova, 24-28 Sept. 2012

  2. Personal characteristics Age Occupation Year of Birth Education Sex Income Marital status Ethnic group/Religion Time Short term variations Long term variations (secular changes) Place International variations Regional variations Local variations Urban/Rural variations Disease determinants: factors of importance for disease occurrence

  3. Gallitto et al. Epilepsia, 2005.

  4. Standardization Standardization allows for comparisons when the population structures differ and is key in assessing the potential influence of environmental or cultural factors on disease rates in a region. A standardized estimate is a crude estimate that has been adjusted for differences in age composition between the study population and a standard (referral) population. Standardized estimate based on the same standard population are comparable and the ratio between two standardized estimates is called Standardized Rate Ratio (SRR) Standardization for gender and age

  5. There are two ways of computing standardized estimates: • Direct Standardization: it calculates a weighted average of the region’s age-specific estimates where the weights represent the age-specific sizes of the standard population. • Indirect Standardization: it uses age-specific estimates (eg., mortality) from the standard population to derive expected estimates (eg., deaths) in the region’s population. • Choosing which formula to use will depend on what data you have access to.

  6. Type of data we can have access to: Direct Standardization (eg., incidence, prevalence, mortality) Indirect Standardization (eg., mortality)

  7. Direct Standardization: To compute the direct standardized mortality rate (SMR): 1. For each age group, you need to multiply Mr by Ps. 2. Add them up. 3. Divide the sum by the total standard population. 4. Multiply by 1000, or give the rate in terms of "per thousand population" SDR1 = [Sum age groups (Mr x Ps)]/Pt x 1000 Mr is the age-specific mortality rate for the region. Ps is the number of people in the age group in the standard population. Pt is the total standard population.

  8. Indirect Standardization: To compute the indirect standardized mortality rate: 1. For each age group, you need to multiply Ms by Pr. 2. Add them up. 3. Divide the sum into the number of deaths in the region. 4. Multiply by the crude death rate. SDR2 = Dr/[Sum age groups (Ms Pr)] x CDRs Ms is the age-specific mortality rate for the standard population. Pr is the number of people in the age group in the region’s population. Dr is the number of deaths in the region. CDRs is the crude death rate for the standard population.

  9. DIRECT METHOD OF STANDARDIZATION Examples

  10. Example: SDR1 = [Sum age groups (Mr x Ps)]/Pt x 1000 Mr is the age-specific mortality rate for the region. Ps is the number of people in the age group in the standard population. Pt is the total standard population

  11. Prevalence of ALS in northern Sardinia (prov. of Sassari and Nuoro) in 2004 The island of Sardinia, Italy Pugliatti M, Parish LD, et al. J Neurol, in press

  12. Prevalence of ALS in northern Sardinia (prov. of Sassari and Nuoro) in 2004 8,9 5,1 6,9 13,1 8,2 10,6 10, 4 6,2 8,3 Pugliatti M, Parish LD, et al. J Neurol, in press

  13. Prevalence and Characteristics of Epilepsy in the Aeolian Islands Gallitto et al. Epilepsia, 2005.

  14. Prevalence and Characteristics of Epilepsy in the Aeolian Islands Gallitto et al. Epilepsia, 2005.

  15. Prevalence and Characteristics of Epilepsy in the Aeolian Islands per 1000 Gallitto et al. Epilepsia, 2005.

  16. * * Gallitto et al. Epilepsia, 2005.

  17. DIRECT METHOD OF STANDARDIZATION Other Examples

  18. Direct standardization The choice of a standard population affects the comparison. Here the Sweden population is used as standard, the Panama rates applied to this population

  19. Direct standardization Here the Panama population is used as standard, the Swedish rates applied to this population

  20. Thank you

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