Measurements of Disease Occurrence- Epidemiology (1).pptx
ImranNazeer20
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Jul 29, 2024
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About This Presentation
Nursing ethics is a discipline of medicine that involves ethical principles and core values that guide nursing practice. Some of the core principles include:
Autonomy
The right of patients to make their own decisions based on their values and beliefs, even if they differ from the nurse's
Benefic...
Slide Content
BASIC MEASUREMENTS OF EPIDEMIOLOGY Ms. Sahar Soomro 1
LEARNING OBJECTIVEs Define and discuss incidence and prevalence, and state the relationship between them Calculate and appraise different measures of rates and ratio. Define crude & specific mortality rates, case fatality rate, proportionate mortality ratio 2
Rate, RATIO, and PROPORTION Measurements of Disease Occurrence
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EXAMPLE: PROPORTION A randomized clinical trial was conducted to test the effectiveness of low-dose aspirin in preventing heart attacks. Subjects were randomly assigned to receive either low-dose aspirin or an inactive placebo. There were 11,027 subjects in the aspirin group, and, after 5 years of observation, there had been a total of 10 fatal heart attacks in this group. What was the proportion having a fatal heart attack in the aspirin group? After computing the decimal fraction, convert your answer into the number of subjects having a fatal heart attack per 10,000 subjects. Round off your answer to the number of (whole) subjects per 10,000. Do not include decimals 5
EXAMPLE: PROPORTION A randomized clinical trial was conducted to test the effectiveness of low-dose aspirin in preventing heart attacks. Subjects were randomly assigned to receive either low-dose aspirin or an inactive placebo. There were 11,027 subjects in the aspirin group, and, after 5 years of observation, there had been a total of 10 fatal heart attacks in this group. What was the proportion having a fatal heart attack in the aspirin group ? After computing the decimal fraction, convert your answer into the number of subjects having a fatal heart attack per 10,000 subjects. Round off your answer to the number of (whole) subjects per 10,000. Do not include decimals. 10/11027 = 0.000906864 This can be converted into the number of fatal heart attacks per 10,000 subjects by moving the decimal point 4 places to the right. This gives 9.06864 per 10,000. If we round off to the nearest whole person, the answer is 9 per 10,000. 6
RATE 7
RATE Rates are a special type of ratio that incorporate the dimension of time into the denominator. Familiar examples include measurements of speed (miles per hour ). For example: A mortality rate is the proportion of deaths occurring over a span of time in a population. An attack rate is the proportion of people developing an infectious disease after exposure to a pathogen. A case-fatality rate is the proportion of individuals who die after developing a disease 8
RATIO 9
SIMPLE RATIO Consider a class that has 20 male students and 80 female students. We can think about this in several ways. We could express this simply as the ratio of men to women and write the relationship as 20:80 or 20/80. We can also simplify this by dividing both the numerator and the denominator by a number that divides evenly into both the numerator and the denominator. In this case, we could divide both by 20 to simplify this to a 1:4 ratio (or 1/4 ratio). This indicates that for every man, there are four women. We could also consider this from the inverse perspective, i.e., the number of women relative to the number of men; in this case the ratio of women to men is 80/20 which is equivalent to 4 to 1, i.e., there are four women for every man. 10
COMMONLY USED MEASURES OF DISEASE occurrence: PREVALENCE INCIDENCE 11
PREVALENCE INCIDENCE 12
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INCIDENCE 16
CUMULATIVE INCIDENCE 17
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EXAMPLE PROBLEMS Among those admitted to a psychiatric treatment center there were carriers of hepatitis B in some wards but not in others. To investigate the extent to which this affected the occurrence of hepatitis B among personnel, employees of the treatment center were examined with regard to the presence of serological markers. Of 67 people working on the wards with carriers, 14 had markers for hepatitis B. Of 72 people working on the other wards, 4 had these markers. Which measure of occurrence of markers can be calculated? Calculate this for each of the two personnel groups. 25
EXAMPLE PROBLEMS Among those admitted to a psychiatric treatment center there were carriers of hepatitis B in some wards but not in others. To investigate the extent to which this affected the occurrence of hepatitis B among personnel, employees of the treatment center were examined with regard to the presence of serological markers. Of 67 people working on the wards with carriers, 14 had markers for hepatitis B. Of 72 people working on the other wards, 4 had these markers. Which measure of occurrence of markers can be calculated? Calculate this for each of the two personnel groups. P1 = 14/67 = 0.21 P0 = 4/72 = 0.06 26
Prevalence PROBLEM 2. In a mass screening of 1,000 65-year-old men, 100 were found to have a certain disease. During the following 10-year period another 200 contracted this disease. Which measure (s) of disease frequency can be calculated? Calculate this/these. 27
PREVALENCE PROBLEM 2. In a mass screening of 1,000 65-year-old men, 100 were found to have a certain disease. During the following 10-year period another 200 contracted this disease. Which measure (s) of disease frequency can be calculated? Calculate this/these . Prevalence at the start = 100 / 1,000 = 0.10 Prevalence at the end= 100 + 200 / 1,000 = 0.30 28
PROBLEM 2. In a mass screening of 1,000 65-year-old men, 100 were found to have a certain disease. During the following 10-year period another 200 contracted this disease. Which measure (s) of disease frequency can be calculated? Calculate cummulative incidence 29
PROBLEM 2. In a mass screening of 1,000 65-year-old men, 100 were found to have a certain disease. During the following 10-year period another 200 contracted this disease. Which measure (s) of disease frequency can be calculated? Calculate cumulative incidence Cummulative Incidence = 200 / (1000 − 100) = 0.22 over a 10-year period 30
Problem During a 5-year period, 270 new cases of duodenal ulcer occurred in the male population of a city. The number of men in the city was 18,500 at the beginning of the period and 21,500 at the end. Which measure of disease occurrence can be calculated? Calculate this. 31
Problem During a 5-year period, 270 new cases of duodenal ulcer occurred in the male population of a city. The number of men in the city was 18,500 at the beginning of the period and 21,500 at the end. Which measure of disease occurrence can be calculated? Calculate this . Number of cases = 270 Average population size = (18,500+21,500) / 2 = 20,000 Observation period = 5 years Total person time at risk = 20,000 x 5 = 100,000 person-years Incidence Rate = 270 / 100,000 = 0.0027 per person-years 32
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