University:
American Career College
Course:
NURS115 | Intermediate Medical
Academic year:

2020
Views:

458

Pages:

40
Author:

olianesmcq

Discussion: Epidemiology I (Health Indicators) Frequency measures •To make comparison between two populations of unequal sizes •To avoid being misled by the increase and decrease of absolute numbers Commonly used frequency measures: Rate Ratio Proportion Ratio •Ratio is a relative magnitude of two quantities •The numerator and denominator are not necessarily related •The formula of the ratio is: •Two different categories of the same variables, e.g. males to females (gender) •The two frequencies from different variables, e.g. doctors to population size •Frequently used in both descriptive and analytic epidemiology (e.g. odds ratio & relative risk ) •Frequently, either the numerator or denominator is divided by the value of either one of them, so it can be expressed as x:1 •A multiplier might be used Example 1 A survey was performed in country A during a specific year to identify diabetic subjects. Among 3000 participants, 200 of them had diabetes mellitus. Calculate the ratio of diabetic to non-diabetic. The number of diabetic participants is 200 The number of non-diabetic participants is 3000 – 200 = 2800 200/200=1, 2800/200 = 14 then ratio of diabetic to non-diabetic = 1 : 14 Example 2 A city with a population of 3,000,000 persons has 500 primary health care centers. Calculate the ratio of centers per person. Divide both quantities by 500 So the ratio becomes 1 center per 6,000 person Or 500/3,000,000 = 0.000166 center per person To be easily understood, we could multiply by a constant, 0.000166 * 10,000 = 1.66 Then the ratio = 1.66 centers per 10,000 Example 3 In a specific year, country A had infant mortality rate was 8 per 1,000 live births, while in country B the infant mortality rate was 4 per 1,000 live births. Calculate the infant mortality ratio in country A to that in country B. Divide both rates by 4, 8/4 = 2 and 4/4 = 1 So the ratio = 2:1 Thus, country A’s infant mortality rate was 2 times as high as country B’s infant mortality rate in that specific year Proportion • It is comparing a part to the whole • Commonly used measure in descriptive epidemiology • The numerator is included in the denominator • Can be expressed as a fraction, a percentage, or a decimal • Can be converted to ratio • The formula of the proportion is Proportions in country A: •The proportion of hypertensive persons is 20% •Half of the population is females. •0.6 of people is younger than 30 years old Previous Example 1 A survey was performed in country A during a specific year to identify diabetic subjects. Among 3000 participants, 200 of them had diabetes mellitus. Calculate the proportion of diabetics. The proportion of diabetics = 200/3000 = 0.066 Could be multiplied by 100 = 6.6% Proportionate Mortality •It is a proportion of fatal cases in a specific population during a period of time due to different causes •It is expressed as a percentage of each cause of death, they add up to 100% Example In country A during a specific year, there were 100,000 deaths. 40,000 caused by cardiovascular diseases, 30,000 caused by malignancies, 10,000 due to accidents and the rest attributed to other causes. The proportionate mortality: Cardiovascular diseases: 40,000/100,000 * 100 = 40% Malignancies : 30,000/100,000 * 100 = 30% Accidents : 10,000/100,000 * 100 = 10% Others : 20,000/100,000 * 100 = 20% They add up to 100% Morbidity Frequency Measures Morbidity is any deviation from the state of psychological and/or physiological well being (disease, injury, and disability) The main measures of morbidity: •Incidence (new cases) •Prevalence (old and new cases) Incidence proportion • It is the proportion of persons with health related condition who were previously free with that condition during a specified period of time • It is also called: Risk Attack rate Cumulative incidence Probability of developing disease Formula to calculate incidence proportion: Example 1 In country A with a population 10,000,000 during a specific year, of whom 1,000,000 had already had cardiovascular diseases. A 50,000 new cases of cardiovascular disease have occurred during that specific year. Calculate the incidence proportion of cardiovascular diseases. The incidence proportion = 50,000/(10,000,000 – 1,000,000) = 0.0055 10,000 * 0.0055 = 55 per 10,000 Example 2 In a study about HIV/AIDS within a specific year, out of 10,000 cases of HIV/AIDS, 50 of them have died. Calculate the risk of death due to HIV/AIDS in this study. The risk = 50/10,000 = 0.005 1,000 * 0.005 = 5 per 1000 Attack rates • Frequently used during outbreaks • (Overall) attack rate: is the number of new cases divided by the total number of people at risk during the period of the outbreak • Example: an outbreak of cholera occurred in town A with a population of 50,000. 120 cases of cholera occurred in the town. The attack rate = 120/50,000 = 0.0024 10,000 * 0.0024 = 24 per 10,000 Secondary attack rate • Sometimes the numerator is: the number of new cases who developed the disease after contacting the primary cases within on incubation period Example Consider an epidemic of influenza in which 20 individuals in 20 different households developed the disease. One incubation period later, 14 more individuals were diagnosed with influenza in the same households. The total number of people in the 20 households is 80. calculate the secondary attack rate. The secondary attack rate = 14/(80-20) = 0.23 100 * 0.23 = 23% Prevalence • Sometimes called “prevalence rate”, it is the proportion of diseased persons in given population during specified period, it includes all cases (new + preexisting) • Point prevalence: it is measured in a particular point of time • Period prevalence: it is measured during defined extended period Example In country B with a population of 20,000,000, during the year of 2019 there were 5,000 new stroke cases. And there had been 17,000 stroke cases before 2019. Calculate in incidence proportion during 2019, and the prevalence of stroke The incidence proportion = 5,000/20,000,000 = 0.00025 100,000 * 0.00025 = 25 per 100,000 The prevalence = (5,000 + 17,000)/20,000,000 = 0.0011 100,000 * 0.0011 = 110 per 100,000 Or (5,000 + 17,000)/ 20,000,000 * 100 = 0.11% •Prevalence depends on incidence and duration of the diseases • incidence prevalence • Duration prevalence •Prevalence is used to measure chronic diseases (e.g. diabetes and hypertension) Prevalence vs. Incidence • Prevalence can be viewed as describing a pool of disease in a population • Incidence describes the input flow of new cases into the pool • Fatality and recovery reflects the output flow from the pool. (from Principles of Epidemiology in Public Health) Mortality Frequency Measures Mortality rate: • It measures the frequency of deaths in defined population within a specific period • The numerator is the number of deaths, while the denominator is the size of population in the middle of the time period • The formula is: Frequently used Mortality Measure (from Principles of Epidemiology in Public Health) Leading causes of Libya Age-specific mortality rate is the mortality rate of a specific age group • The numerator is the number of deaths among a specific age group • The denominator is the total number of people in that specific age group Sex-specific mortality rate is the mortality rate of a specific sex (meals or females) • The numerator is the number of deaths among e.g. females • The denominator is the total number of females Race-specific mortality rate: is the mortality rate of a specific race • The numerator is the number of deaths among a specific race • The denominator is the total number of people in that specific race Case-fatality rate: it measures the severity of the disease