Biostatsu

[QUESTION Ratio] What is the definition of a ratio in epidemiology?

[Answer: A ratio is a measure that compares the relative magnitude of two measurements, such as the number of male cases to female cases, without requiring the denominator to be a total population (p. 11).

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[QUESTION Proportion] What is the definition of a proportion in epidemiology?

[Answer: A proportion is a measure that represents the fraction of a population with a specific characteristic or outcome, such as the percentage of literate children, with the denominator as the total group (p. 26).

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[QUESTION Odds Ratio] What is the definition of an odds ratio (OR) in epidemiology?

[Answer: An odds ratio is a measure that compares the odds of an event occurring in an exposed group to the odds in an unexposed group, commonly used in case-control studies to assess exposure-outcome associations (p. 16).

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[QUESTION Natality] What is the definition of natality in epidemiology?

[Answer: Natality is a measure that quantifies the occurrence of births in a population, often expressed through birth rates to assess population growth (p. 34).

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[QUESTION Morbidity] What is the definition of morbidity in epidemiology?

[Answer: Morbidity is a measure that represents the rate of illness or disease in a population, used to track disease spread and identify causative factors (p. 36).

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[QUESTION Mortality] What is the definition of mortality in epidemiology?

[Answer: Mortality is a measure that represents the frequency of deaths in a population over a specified period, often analyzed by cause or demographic group (p. 50).

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[QUESTION Crude Birth Rate] What is the definition of the crude birth rate (CBR) in epidemiology?

[Answer: The crude birth rate is a natality measure that indicates the number of live births occurring in a population per unit of time, typically per 1,000 people, using the total population (p. 34).

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[QUESTION Crude Fertility Rate] What is the definition of the crude fertility rate (CFR) in epidemiology?

[Answer: The crude fertility rate is a natality measure that indicates the number of live births per unit of time, typically per 1,000 women aged 15–44, focusing on the reproductive age group (p. 34).

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[QUESTION Point Prevalence] What is the definition of point prevalence in epidemiology?

[Answer: Point prevalence is a morbidity measure that represents the proportion of a population with a specific disease at a particular point in time, such as a single day (p. 39).

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[QUESTION Period Prevalence] What is the definition of period prevalence in epidemiology?

[Answer: Period prevalence is a morbidity measure that represents the proportion of a population with a specific disease at any time during a defined period, including both new and existing cases (p. 39).

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[QUESTION Cumulative Incidence] What is the definition of cumulative incidence in epidemiology?

[Answer: Cumulative incidence is a morbidity measure that represents the probability or risk of developing a disease over a specified period among the population at risk at the start (p. 40).

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[QUESTION Incidence Rate] What is the definition of incidence rate in epidemiology?

[Answer: Incidence rate is a morbidity measure that represents the rate of new disease cases occurring per unit of person-time at risk over a specified period (p. 40).

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[QUESTION Crude Mortality Rate] What is the definition of the crude mortality rate (CMR) in epidemiology?

[Answer: The crude mortality rate is a mortality measure that represents the rate of deaths from all causes in a population per unit of time, typically per 1,000 people (p. 51).

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[QUESTION Cause-Specific Death Rate] What is the definition of the cause-specific death rate (CSDR) in epidemiology?

[Answer: The cause-specific death rate is a mortality measure that represents the rate of deaths from a specific cause in a population per unit of time, typically per 1,000 people (p. 51).

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[QUESTION Case Fatality Rate] What is the definition of the case fatality rate (CFR) in epidemiology?

[Answer: The case fatality rate is a mortality measure that represents the proportion of individuals with a specific disease who die from it over a specified period (p. 52).

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[QUESTION Proportionate Mortality Rate] What is the definition of the proportionate mortality rate (PMR) in epidemiology?

[Answer: The proportionate mortality rate is a mortality measure that represents the proportion of total deaths in a population that are attributed to a specific cause over a specified period (p. 52).

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[QUESTION Infant Mortality Rate] What is the definition of the infant mortality rate (IMR) in epidemiology?

[Answer: The infant mortality rate is a mortality measure that represents the proportion of babies aged 0–365 days who die per total live births in a specified period (p. 55).

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[QUESTION General Morbidity Rate] What is the definition of the general morbidity rate in epidemiology?

[Answer: The general morbidity rate is a morbidity measure that represents the rate of illness in a population over a specified period, used to monitor disease trends and guide interventions (p. 36).

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[QUESTION Sex-Specific Death Rate] What is the definition of the sex-specific death rate (SSDR) in epidemiology?

[Answer: The sex-specific death rate is a mortality measure that represents the rate of deaths within a specific sex group, such as males or females, over a specified period (p. 53).

]Problem 1: Ratio A study records 150 male cases of a disease and 100 female cases of the same disease. Calculate the simple sex ratio.

[Answer: (150/100) = 1.5 + The simple sex ratio compares the number of male cases to female cases, expressed as 150 males per 100 females, which simplifies to 1.5. This indicates 1.5 times more male cases than female cases (p. 13).

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Problem 2: Proportion In a community of 500 people, 75 are diagnosed with diabetes. What is the proportion of the population with diabetes?

[Answer: (75/500) = 0.15 + The proportion is the fraction of the total population with the condition, calculated as 75 cases divided by 500 people, resulting in 0.15 or 15% of the community having diabetes (p. 26).

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Problem 3: Odds Ratio (OR) A case-control study finds: 60 cases of lung disease (40 exposed to air pollution, 20 unexposed), and 80 controls (30 exposed to air pollution, 50 unexposed). Calculate the odds ratio.

[Answer: ((40×50)/(20×30)) = (2000/600) = 3.33 + The odds ratio is calculated using (a×d)/(b×c), where a = 40 (exposed cases), b = 30 (exposed controls), c = 20 (unexposed cases), d = 50 (unexposed controls). This gives an OR of 3.33, meaning the odds of lung disease are 3.33 times higher with air pollution exposure than without (p. 17).

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Problem 4: Natality – Crude Birth Rate (CBR) A city has a mid-interval population of 20,000 and records 400 live births in 2024. Calculate the crude birth rate per 1,000.

[Answer: (400/20,000) × 1,000 = 20 + The crude birth rate is (Total live births/Mid-interval population) × 1,000, yielding 400/20,000 × 1,000 = 20 births per 1,000 people, reflecting the birth rate using the mid-year population estimate (p. 34).

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Problem 5: Natality – Crude Fertility Rate (CFR) A region has a mid-interval population of 5,000 women aged 15–44 and 150 live births in 2024. Calculate the crude fertility rate per 1,000.

[Answer: (150/5,000) × 1,000 = 30 + The crude fertility rate is (Total live births/Mid-interval population of women aged 15–44) × 1,000, resulting in 150/5,000 × 1,000 = 30 births per 1,000 women, focusing on the reproductive age group (p. 34).

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Problem 6: Morbidity – Point Prevalence On May 16, 2025, at 2:05 PM PST, a town of 1,000 people has 120 individuals with a chronic condition. Calculate the point prevalence.

[Answer: (120/1,000) = 0.12 + Point prevalence is (Persons with disease on a point date/Total persons on a point date), giving 120/1,000 = 0.12 or 12% of the population with the condition at that specific moment (p. 39).

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Problem 7: Morbidity – Period Prevalence Over the past year (May 16, 2024, to May 16, 2025), 150 people in a population of 2,000 had a seasonal illness at some point. Calculate the period prevalence.

[Answer: (150/2,000) = 0.075 + Period prevalence is (Persons with disease within a time period/Total persons within a time period), resulting in 150/2,000 = 0.075 or 7.5% of the population affected over the year (p. 39).

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Problem 8: Morbidity – Cumulative Incidence In a cohort of 500 people followed from January to December 2024, 25 new cases of a disease were identified. Calculate the cumulative incidence.

[Answer: (25/500) = 0.05 + Cumulative incidence is (New cases within a time period/Total persons at the beginning of a time period), giving 25/500 = 0.05 or 5% probability of developing the disease over the year (p. 40).

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Problem 9: Morbidity – Incidence Rate Over 6 months, 30 new cases of a disease occurred in a population with a total person-time at risk of 1,200 months. Calculate the incidence rate.

[Answer: (30/1,200) = 0.025 + Incidence rate is (New cases within a time period/Total person-time at risk), resulting in 30/1,200 = 0.025 or 25 cases per 1,000 person-months (p. 40).

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Problem 10: Mortality – Crude Mortality Rate (CMR) A town with a mid-interval population of 15,000 recorded 225 deaths in 2024. Calculate the crude mortality rate per 1,000.

[Answer: (225/15,000) × 1,000 = 15 + The crude mortality rate is (Total deaths in a time period/Mid-interval population) × 1,000, yielding 225/15,000 × 1,000 = 15 deaths per 1,000 people, using the mid-year population (p. 51).

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Problem 11: Mortality – Cause-Specific Death Rate (CSDR) In a mid-interval population of 10,000, 80 deaths were due to heart disease in 2024. Calculate the cause-specific death rate per 1,000.

[Answer: (80/10,000) × 1,000 = 8 + The cause-specific death rate is (Deaths due to a disease in a time period/Mid-interval population) × 1,000, resulting in 80/10,000 × 1,000 = 8 deaths per 1,000 people from heart disease (p. 51).

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Problem 12: Mortality – Case Fatality Rate (CFR) In 2024, a disease affected 200 people, and 40 died from it. Calculate the case fatality rate.

[Answer: (40/200) = 0.2 + The case fatality rate is (Deaths due to a disease in a time period/Total cases of the disease in a time period), giving 40/200 = 0.2 or 20% of cases resulting in death (p. 52).

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Problem 13: Mortality – Proportionate Mortality Rate (PMR) In 2024, a population had 300 total deaths, with 60 due to cancer. Calculate the proportionate mortality rate for cancer.

[Answer: (60/300) = 0.2 + The proportionate mortality rate is (Deaths due to a disease in a time period/Total deaths in a time period), resulting in 60/300 = 0.2 or 20% of all deaths attributed to cancer (p. 52).

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Problem 14: Mortality – Infant Mortality Rate (IMR) In 2024, a region had 1,000 live births, and 15 babies died before age 1. Calculate the infant mortality rate.

[Answer: (15/1,000) = 0.015 + The infant mortality rate is (Deaths in babies aged 0–365 days in a time period/Total live births in a time period), giving 15/1,000 = 0.015 or 15 deaths per 1,000 live births (p. 55).

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[QUESTION Ratio] What is the formula for a ratio in epidemiology?

[Answer: (X/Y) + This formula compares two distinct measurements, such as the number of male cases (X) to female cases (Y), to show their relative magnitude, as seen in the simple sex ratio example (p. 13).

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[QUESTION Proportion] What is the formula for a proportion in epidemiology?

[Answer: (Part/Total) + This formula measures the fraction of a population with a specific characteristic, such as the number of literate children (part) out of the total children (p. 27).

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[QUESTION Odds Ratio] What is the formula for the odds ratio (OR) in epidemiology?

[Answer: ((a×d)/(b×c)) + This formula calculates the odds ratio, where a is exposed cases, b is exposed controls, c is unexposed cases, and d is unexposed controls, showing the odds of an outcome with exposure versus without (p. 17).

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[QUESTION Natality – Crude Birth Rate] What is the formula for the crude birth rate (CBR) in epidemiology?

[Answer: (Total live births/Mid-interval population) × 1,000 + This formula calculates the number of live births per 1,000 people in the total population over a specified period, using the mid-interval population for accuracy (p. 34).

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[QUESTION Natality – Crude Fertility Rate] What is the formula for the crude fertility rate (CFR) in epidemiology?

[Answer: (Total live births/Mid-interval population of women aged 15–44) × 1,000 + This formula measures the number of live births per 1,000 women aged 15–44, focusing on the reproductive age group (p. 34).

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[QUESTION Morbidity – Point Prevalence] What is the formula for point prevalence in epidemiology?

[Answer: (Persons with disease on a point date/Total persons on a point date) + This formula measures the proportion of a population with a disease at a specific moment, such as on April 1, 2005 (p. 39).

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[QUESTION Morbidity – Period Prevalence] What is the formula for period prevalence in epidemiology?

[Answer: (Persons with disease within a time period/Total persons within a time period) + This formula measures the proportion of a population with a disease (new and existing cases) over a specified period, like 15 months (p. 39).

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[QUESTION Morbidity – Cumulative Incidence] What is the formula for cumulative incidence in epidemiology?

[Answer: (New cases within a time period/Total persons at the beginning of a time period) + This formula measures the probability of developing a disease over a period among the population at risk at the start (p. 40).

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[QUESTION Morbidity – Incidence Rate] What is the formula for incidence rate in epidemiology?

[Answer: (New cases within a time period/Total person-time at risk) + This formula measures the rate of new cases per unit of person-time at risk, accounting for varying follow-up times (p. 40).

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[QUESTION Mortality – Crude Mortality Rate] What is the formula for the crude mortality rate (CMR) in epidemiology?

[Answer: (Total deaths in a time period/Mid-interval population) × 1,000 + This formula measures the rate of deaths from all causes per 1,000 people in the population, using the mid-interval population (p. 51).

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[QUESTION Mortality – Cause-Specific Death Rate] What is the formula for the cause-specific death rate (CSDR) in epidemiology?

[Answer: (Deaths due to a disease in a time period/Mid-interval population) × 1,000 + This formula measures the rate of deaths from a specific cause per 1,000 people in the population (p. 51).

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[QUESTION Mortality – Case Fatality Rate] What is the formula for the case fatality rate (CFR) in epidemiology?

[Answer: (Deaths due to a disease in a time period/Total cases of the disease in a time period) + This formula measures the proportion of individuals with a disease who die from it over a period (p. 52).

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[QUESTION Mortality – Proportionate Mortality Rate] What is the formula for the proportionate mortality rate (PMR) in epidemiology?

[Answer: (Deaths due to a disease in a time period/Total deaths in a time period) + This formula measures the proportion of all deaths attributed to a specific cause (p. 52).

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[QUESTION Mortality – Infant Mortality Rate] What is the formula for the infant mortality rate (IMR) in epidemiology?

[Answer: (Deaths in babies aged 0–365 days in a time period/Total live births in a time period) + This formula measures the proportion of babies under 1 year who die per total live births in a period (p. 55).

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[QUESTION Morbidity – General Morbidity Rate] What is the formula for the general morbidity rate in epidemiology?

[Answer: (Number of events in a time period/Number of people at risk in a time period) × 10^n + This formula measures the rate of illness in a population over a specified period, used to control disease spread and identify causes (p. 36).

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[QUESTION Mortality – Sex-Specific Death Rate] What is the formula for the sex-specific death rate (SSDR) in epidemiology?

[Answer: (Deaths in a sex group in a time period/Total population of the sex group) + This formula measures the death rate for a specific sex group, such as males or females, over a period (p. 53).

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