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Measure of Disease Frequency

Measure of Disease Frequency. รศ.ดร.ทรงชัย ฐิตโสมกุล. Basic measurement. Risk Prevalence Incidence rate Survival Case fatality. Risk . Cumulative incidence Measure the new cases in the population

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Measure of Disease Frequency

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  1. Measure of Disease Frequency รศ.ดร.ทรงชัย ฐิตโสมกุล

  2. Basic measurement • Risk • Prevalence • Incidence rate • Survival • Case fatality

  3. Risk • Cumulative incidence • Measure the new cases in the population • Is the proportion of unaffected individuals who, on average, will contract the disease of interest over a specified period of time • อัตราส่วนของผู้ที่เกิดโรครายใหม่ในประชาการที่มีความเสี่ยงในการเกิดโรคใด ๆ ในระยะเวลาที่กำหนด

  4. Risk • ไม่มีหน่วยนับ • มีค่า 0 – 1 • คูณด้วย 100 จะได้เป็น เปอร์เซ็นต์

  5. death diagnosis diagnosis 1982 1984 1986 1988 1990

  6. Risk of disease within 2 years = ?

  7. Risk of high ECC as high plaque score=?

  8. Prevalence Prevalence indicates the number of exiting cases in a population Prevalence is the proportion of a population that has the disease of interest at a particular time i.e. year, week or day. ความชุกของการเกิดโรค คือ อัตราส่วนของคนที่เป็นโรคในประชากรที่สนใจ ณ เวลาใด เวลาหนึ่ง

  9. What is the prevalence of disease affected on year 1988? death diagnosis diagnosis 1982 1984 1986 1988 1990

  10. Prevalence • ไม่มีหน่วยนับ • มีค่า 0 – 1 • คูณด้วย 100 จะได้เป็น เปอร์เซ็นต์

  11. Incidence Rate • The incidence rate, like risk, reflects occurrence of new cases of disease. • Incidence rate measures the rapidity with which newly diagnosed patients develop over time อุบัติการณ์ เป็นการวัดความเร็วของการเกิดโรคใด ๆ ในระยะเวลาที่กำหนด PT= the person-time at risk

  12. Incidence Rate How to get person-time? death diagnosis diagnosis 1982 1984 1986 1988 1990

  13. death diagnosis diagnosis 1982 1984 1986 1988 1990 2 years 2 years 3 years 7 years 2 years 6 years

  14. IR= 0.09 cases/person-year IR= 9 cases/100 person-years

  15. PT= (average size of population at risk) X (length of observation) PT= (size of entire population) X (length of observation) ในทางทันตแพทย์ เนื่องจากฟันผุเป็นโรคเรื้อรังที่ไม่ทราบวันที่ผุชัดเจน จะต้องทำอย่างไร

  16. Characteristics of risk, prevalence and incidence rate

  17. Survival • Survival is the probability of remaining alive for a specific length of time • 1-year survival, 5-year survival • 5-year survival of lung cancer is 0.13 • Only 13% of lung cancer patients survive at least 5 years after diagnosis

  18. death death diagnosis diagnosis death death diagnosis diagnosis 1982 1984 1986 1988 1990 1982 1984 1986 1988 1990 What is the survival rate at least 2 years?

  19. Case fatality • Case fatality is the proportion of persons affected by a particular disease who die from it within a specified period of time

  20. Death Disease No death Population at risk No disease The case fatality =?

  21. Exercise • 10 multiple choice questions

  22. Comparing disease frequency

  23. Comparing disease frequency • Organize disease frequency into a two-by-two table • Find absolute or relative comparison • Rate/risk difference • Population rate/risk difference • Attributable among the exposed and the total population • Rate ratio or risk ratio

  24. Two-by-two table for Prevalence

  25. Two-by-two table for incidence rate ทำไมช่องนี้ต้องหายไป

  26. Absolute or relative comparison • Absolute: difference btw 2 measurements • Called: risk difference or rate difference • ie. Incidence rate difference • Cumulative incidence difference • Prevalence difference The commonly used term: attributable risk or attributable rate

  27. Risk difference or rate difference

  28. risk difference or rate difference • จงหา risk differenceระหว่าง ความฟันผุในเด็กที่กินน้ำตาล และไม่กินน้ำตาล พร้อมทั้งแปลผล

  29. Incidence rate difference • จงหา incidence rate differenceระหว่าง ความฟันผุในเด็กที่กินน้ำตาล และไม่กินน้ำตาล พร้อมทั้งแปลผล

  30. Population rate difference (PRD)

  31. Population rate difference (PRD) • 25% of Thai children exposed to sugary food • What is the PRD for Thai children? • What does in mean?

  32. Attributable proportion among the exposed (APe) • Unit in percent • What does it mean? • Describes the proportion of disease among the exposed the would be eliminated if the exposure were eliminated • Use the provided data to compute (APe) of sugary food exposed. 62 % of the caries affected children caused by high sugary food intake

  33. Attributable proportion among the total population (APt) • Unit in percent • What does it mean? • Describes the proportion of disease among population would be eliminated if the exposure were eliminated: use to prioritized problem! • Use the provided data to compute (APt) of sugary food exposed. Given Rt = 5.6/100 person-years

  34. If that factor has preventive effect! • Children in Hatyai where F in drinking water supply given the incidence of 14.8% caries. Songkhla has non-f given 21.3% caries incidence. • What is the PF of F in drinking water? • What does it mean? We could calculate “Preventive Fraction” or PF

  35. Relative measurement of comparison • This measurement in based on the ratio of two measures of disease frequency • Risk ratio • Rate ratio • Relative rate • Relative risk • Commonly used are incidence rate ratio, cumulative incidence rate ratio or prevalence ratio

  36. Relative measurement of comparison • Unit: TIME • >1 is risk, <1 is protective • Commonly used in etiologic research • What does it mean? • Describes the strength of the relationship btw exposure and disease • Use the provided data to compute (RR) of sugary food exposed.

  37. Standardized mortality ratio (SMR) • SMR used as the measure of association btw groups. • SMR the ratio of the observation number of cases of disease or death to the expected number based on general population rates. • SMRs usually “standardized” or control for age, gender, race, time • SMR interpreted like relative risk. • 21,863 worker, later found die from cancer: 1,083 male and 1012 female • SMR= 1083/1012= 1.07

  38. References • 1. Thitasomakul S, Thearmontree A, Piwat S, Chankanka O, Pithpornchaiyakul W, Teanpaisan R, et al. A longitudinal study of early childhood caries in 9- to 18-month-old Thai infants. Community Dent Oral Epidemiol. 2006 Dec;34(6):429-36. • 2. Greenberg R, Daniels S, Flanders W, Eley J, Boring J. Medical epidemilogy. Connecticut: Appleton&Lange; 1993. • Kahn H, Sempos C. Statistical methods in epidemiology. New York: Oxford university press; 1989. • Aschengrau A, Seage III GR. Essentials of Epidemiology in public health; 2003.

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