1. EPIDEMIOLOGY Lecture 2: Measuring Disease Frequency

2. What did we learn in Lecture 1? A quick Recap Definition of epidemiology The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the prevention and control of health problems The Epidemiological Approach Asking Questions Making comparisons The aims of epidemiology Describe disease Distribution, frequency Identify etiological factors Provide data for planning and implementation and for priority setting 3. Lecture Objectives By the end of this lecture, the student will be able to: 1. Describe the tools of measurements in epidemiology. 2. Enumerate the FIVE elements in a rate. 3. Define and differentiate between incidence and prevalence. 4. Enumerate types of prevalence. 5. Calculate the prevalence of a disease/health- related behavior in a population. 4. Definitions and terms Operational Definition: A definition embodying criteria used to identify and classify individual members of a set or concept to facilitate classification and counting. Population at risk: People who are potentially susceptible to the disease under study. The group of people, healthy or sick, who would be counted as cases if they had the disease being studied. 5. Tools of Measurement in Epidemiology 6. RATIO The value obtained by dividing one quantity by another Example: Sex ratio, Child-woman ratio 7. RATE the frequency with which an event occurs in a defined population, usually in a specified period of time. Example: Incidence rate 8. PROPORTION The ratio of a part to the whole, expressed as a decimal fraction (e.g., 0.2), as a common fraction (1/5), or as a percentage (20%). The proportion is a dimensionless quantity. Example: Proportion of diabetics in a population. 9. The FIVE elements (or components) of a rate Rate = Number of events in a specified population during a specified period Average population during the period X 10 n Numerator Denominator Multiplier Time Population 10. INCIDENCE AND PREVALENCE 11. INCIDENCE WHAT IS IT? the number of new health-related events in a defined population within a specified period of time. It may be measured as a frequency count, a rate, or a proportion. 12. PREVALENCE WHAT IS IT? total number of individuals who have an attribute or disease at a particular time (it may be a particular period) divided by the population at risk of having the attribute or disease at that time or midway through the period. A measure of occurrence or disease frequency, often used to refer to the proportion of individuals in a population who have a disease or condition. When used without qualification, the term usually refers to the situation at a specified point in time (point prevalence). It is a proportion, not a rate. 13. PREVALENCE 14. Definition of prevalence total number of individuals who have an attribute or disease at a particular time (it may be a particular period) divided by the population at risk of having the attribute or disease at that time or midway through the period. A measure of occurrence or disease frequency, often used to refer to the proportion of individuals in a population who have a disease or condition. It refers to NEW+OLD cases of the disease. 15. How is prevalence calculated? Numerator Denominator Multiplier 16. Point prevalence The proportion of individuals with a disease or an attribute at a specified point in time. Types of prevalence 17. Period prevalence The proportion of individuals with a disease or an attribute at a specified period of time. To calculate a period prevalence, the denominator used most commonly is the population at risk midway through the period (e.g., mid-year population) Types of prevalence contd 18. Lifetime prevalence The proportion of individuals who have had the disease or condition for at least part of their lives at any time during their lifecourse. Types of prevalence contd 19. Factors influencing prevalence 20. Estimate the magnitude of health/disease problems in the community and identify potential high-risk population groups. Assessing the need for preventive action, healthcare and the planning of health services. Prevalence is a useful measure of the occurrence of conditions for which the onset of disease may be gradual, such as hypertension, diabetes or rheumatoid arthritis. Uses of prevalence 21. Prevalence studies do not usually provide strong evidence of causality. Disadvantages of prevalence 22. EXERCISES Calculate the prevalence of disease in the given situations. SITUATION 1: In a population of 30000, 200 adolescents girls are anemic. Calculate the prevalence of anemia among adolescent girls if adolescent girls comprise 10% of the population? 23. SITUATION 2: Jan 1, 2013 Dec 31, 2013 Population at risk =200 (on 1st July, 2013)