10. Incidence density.pptx...............

Epidemiology

1. Duhok pol y technic university Shekhan polytechnic college Public health department Incidence density Prepared by Marwa baker Nasreen aziz Nargiz . Rasul Supervised by Dr . Alaa noori Academic year 2022-2023

2. Subject content Introduction Measures of disease occurrence Different between (IP), (IR) and prevalence How to calculate incidence rate Example of calculating Why it’s important? What is person-time?

3. I ntroduction   The term incidence density refers to the rate at which a new event occurs over a specified period of time. Put simply, the incidence rate is the number of new cases within a time period (the numerator) as a proportion of the number of people at risk for the disease (the denominator).This measure is commonly use in epidemiology as a way to denote the occurrence of disease, illness, or accident. This rate only uses new cases . Its also known as the incidence rate or incidence density rate or person-time incidence rate .

4. Measures of Disease occurrence All three are loosly called (rates) . (but only the second is a true rate ) .   1- Incidence proportion (risk) or (IP)   2- Incidence rate (density) or (IR)   3- prevalence

5. Different between them   Incidence proportion and rate Incidence rate and prevalence

6. Incidence density Incidence density ID : Also known as incidence rate the number of observed events divided by the population _time at risk , is often calculated in applications. Examples include studies of cardiovascular disease ,human immunodeficiency virus (HIV) Infection , and hospital _acquired infection . IDs are attractive because they are computationally simple and allow for right –censoring as well as left truncation

7. Incidence density 1-Suggests ability to extrapolate over time (duration free) 2-Accommodates -multiple events in one subject -different follow –up times for subjects 3-Does not require a cohort to estimate or interpret 4-May be more appropriate for etiologic inference

8. How to calculate incidence density

9. Example of calculating Example : In 2003, 44,232 new cases of acquired immunodeficiency syndrome (AIDS) were reported in the United States. The estimated mid-year population of the U.S. in 2003 was approximately 290,809,777. Calculate the incidence rate of AIDS in 2003. Numerator = 44,232 new cases of AIDS Denominator = 290,809,777 estimated mid-year population 10n = 100,000 Incidence rate = (44,232 ⁄ 290,809,777) × 100,000 = 15.21 new cases of AIDS per 100,000 population  

10. Why incidence rate is important   Incidence rate measures are useful when describing how quickly disease occurs in a population. This information can be used to monitor the effectiveness of vaccination schemes or changes in the preventative measures being used to see if they cause a knock-on reduction in disease incidence rate. Equally, if incidence rates rise, it can act as a warning that existing preventative measures are failing and therefore guide remedial action. What is “person-time”? •One person at risk of a disease observed for 1 year = 1 person-year. •One person at risk of a disease observed for 1 month = 1 person-month. •Person-time has units, e.g. year-1 or month-1.  

11. References 1.Williams R, Wright J. Epidemiological issues in health needs assessment. BMJ. 1998;316:1379. 2-Biermans M, Verheij R, De Bakker D, Zielhuis G, De Vries Robbé P. Estimating morbidity rates from electronic medical Records in General Practice: evaluation of a grouping system. Methods Inf Med. 2008;47:98–106. 3-http://www.ncbi.nlm.gov   4- http://core.ac.uk 5- http://www.brusheducation.ca