HMB342H1 Lecture Notes - Lecture 3: Cohort Study, Cumulative Incidence, Prevalence

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19 Apr 2016

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Fraction or proportion of a group of people initially free of the outcome of interest that develops the condition over a given period of time: cumulative incidence new cases that accumulate over time. Incidence density (person-years) number of new cases emerging in an ever-changing population, one in which individuals are under study and susceptible for varying lengths of time. Prevalence time is assumed to be instantaneous; whereas incidence time is the interval during which susceptible people were observed for the emergence of the event of interest. Prevalence answers: what proportion of a group of people has a condition? ; whereas incidence answers: at what rate do new cases arise in a defined population as time passes? : characteristic. New cases occurring during a period of time among a group initially free of disease. All susceptible people without disease at the beginning of the period. Existing cases at a point or period of time.

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do you agree or disagree and why? + source of the information:

A prevalence proportion differs from an incidence rate by specified cases and time period. A prevalence rate focuses on all kinds of existing cases while incidence rate focuses on new cases of disease. Incidence rate is calculated by dividing the number of new cases over a certain period of time by the population number that is at risk at that same time. The prevalence proportion can be calculated by the number of all existing illness and deaths at a specific time divided by the number of people in that population. There is also point prevalence, which the prevalence is measured at a certain point and period prevalence which measures prevalence over a period of time. To estimate the future risk of breast cancer among women aged 50-65, Incidence rate would be a better indicator since it focuses on the new cases and divides that number by the average population that is at risk at that certain time. It would be better at indicating the risk for women of that specific age group. When estimating the number of surgeons to treat breast cancer a prevalence proportion would be a better indicator. Because a prevalence proportion focuses on all cases and not just new cases, it can measure the ratio of how many surgeons will be needed to treat all people vs just new cases.

1. The risk of acquiring disease is measured by the

a. Incidence rate

b. Incidence rate times the average duration of the disease

c. Incidence rate divided by the prevalence rate

d. Prevalence rate

e. Prevalence rate times the average duration of the disease

2. The strength of an association between a factor and a disease is best measure by .

a. Incubation rate

b. Incidence of the disease in the total population

c. Prevalence of the factor

d. Attributable risk

e. Relative risk

3. Case fatality rate for a given disease refers to

a. The crude mortality rate per 100,000 population

b. Cause-specific mortality rate due to the disease

c. A fatal outcome of any disease

d. The percentage of deaths among cases of the disease

e. The proportion of deaths due to the disease among all deaths from all causes

4. An investigator is interested in etiology of neonatal jaundice. To study this condition, he selected 100 children who were diagnosed with this condition and 100 children born in the same period and in the same hospital who did not have a diagnosis of neonatal jaundice. He then reviewed the obstetrical and delivery records of their mothers to determine various prenatal and perinatal exposures. This is an example of a(n):

a. Cross-sectional study

b. Case-control study

c. Cohort study

d. Clinical trial

e. Experiment

5. Which of the following statements describes the major advantages of a randomized clinical trial?

a. It avoids observer bias

b. It lends itself to ethical justification

c. It yields results replicable in other patients

d. It rules out self-selection of participants to the different treatment groups

d. It enrolls representative patients

a. Correct b.

Incorrect because of failure to distinguish between incidence and prevalence

c. Incorrect because a proportionate ratio is used when a rate is required to support the inference

d. Incorrect because a failure to recognize a possible cohort phenomenon

e. Incorrect because there is no control or comparison group.

7. An investigator determines the correlation coefficient between triglyceride levels and degree of atherosclerosis in sampled blood vessels to be +1.67. On the basis of this you would conclude that:

a. Triglyceride level is a good predictor of atherosclerosis

b. Triglyceride level is not a good predictor of atherosclerosis

c. High triglyceride levels cause atherosclerosis

d. Atherosclerosis cause high triglyceride levels

e. The investigator has incorrectly determined the correlation coefficient

a. The percent of all negative tests that have false-negative results is lower in population A than in population B.

b. Specificity is lower in population A than in population B.

c. Reliability is higher in population A than in population B.

d. The percent of all positive tests that have false-positive results is lower in population A than in population B.

e. Specificity is higher in population A than in population B.

9. Serum cholesterol levels are obtained for four healthy men. The probability that all will fall below the 10th percentile of the distribution of cholesterol for healthy males is:

a. 0.4

b. 1 â (0.1)4

c. (0.1)4

d. (0.9)4

e. Cannot be determined from these data

10. In a diabetes screening program, the screening level for a positive blood sugar level in test 1 is set at 160 mg/dl, and in test 2 at 130 mg/dl. The sensitivity is:

a. Greater in test 1

b. Greater in test 2

c. Equal in test 1 and 2

d. Dependent on the size of the population being evaluated

1. The risk of acquiring disease is measured by the a. Incidence rate b. Incidence rate times the average duration of the disease c. Incidence rate divided by the prevalence rate d. Prevalence rate e. Prevalence rate times the average duration of the disease

2. The strength of an association between a factor and a disease is best measure by a. Incubation rate b. Incidence of the disease in the total population c. Prevalence of the factor d. Attributable risk e. Relative risk

3. Case fatality rate for a given disease refers to a. The crude mortality rate per 100,000 population b. Cause-specific mortality rate due to the disease c. A fatal outcome of any disease d. The percentage of deaths among cases of the disease e. The proportion of deaths due to the disease among all deaths from all causes

5. Which of the following statements describes the major advantages of a randomized clinical trial? a. It avoids observer bias b. It lends itself to ethical justification c. It yields results replicable in other patients d. It rules out self-selection of participants to the different treatment groups d. It enrolls representative patients

6. A survey conducted in England revealed that of 224 families in which there had been a known case of poliomyelitis, 56 maintained parakeets as a family pet. In another British survey, 30 out of 99 poliomyelitis patients questioned kept parakeets. The inference that there is some relationship between the presence of a parakeet in a household and the occurrence of poliomyelitis among household members is a. Correct b. Incorrect because of failure to distinguish between incidence and prevalence c. Incorrect because a proportionate ratio is used when a rate is required to support the inference d. Incorrect because a failure to recognize a possible cohort phenomenon e. Incorrect because there is no control or comparison group.

7. An investigator determines the correlation coefficient between triglyceride levels and degree of atherosclerosis in sampled blood vessels to be +1.67. On the basis of this you would conclude that: a. Triglyceride level is a good predictor of atherosclerosis b. Triglyceride level is not a good predictor of atherosclerosis c. High triglyceride levels cause atherosclerosis d. Atherosclerosis cause high triglyceride levels e. The investigator has incorrectly determined the correlation coefficient

8. A screening test of known sensitivity and specificity is applied to two populations. The prevalence of the disease being screened for is 10% in population A and is 1% in population B. Which of the following is true? a. The percent of all negative tests that have false-negative results is lower in population A than in population B. b. Specificity is lower in population A than in population B. c. Reliability is higher in population A than in population B. d. The percent of all positive tests that have false-positive results is lower in population A than in population B. e. Specificity is higher in population A than in population B.

9. Serum cholesterol levels are obtained for four healthy men. The probability that all will fall below the 10th percentile of the distribution of cholesterol for healthy males is: a. 0.4 b. 1 â (0.1)4 c. (0.1)4 d. (0.9)4 e. Cannot be determined from these data

10. In a diabetes screening program, the screening level for a positive blood sugar level in test 1 is set at 160 mg/dl, and in test 2 at 130 mg/dl. The sensitivity is: a. Greater in test 1 b. Greater in test 2 c. Equal in test 1 and 2 d. Dependent on the size of the population being evaluated

Part II 1.The California Occupational Mortality study data set was employed to assess mortality data for the years 1979-1981. A 2% sample of employed persons from the 1980 census of California was used. It contains the occupation of each person who had died. This study, like any occupation-based study, is restricted to the work life span as far as age of subjects is concerned. This study used ages 16-64 years. Certain persons, because of their source of work, were excluded as subjects: homemakers, retired persons, students, disabled, military personnel, etc. Only main-stream-type employment was used in this study to establish occupations at risk for heavy alcohol drinking. Using the Table below, answer the following:

1.What occupations are most vulnerable to acquiring cirrhosis of the liver from heavy drinking?

2.List several of the occupations identified by the research studies that are more vulnerable to alcohol-induced, cirrhosis related deaths and that have the highest mortality rates.

3. What are possible confounding variables for the research in occupations and heavy drinking that lead to fatal diseases?

4. Based on available research data, develop and construct a web of causation along with the appropriate decision trees for occupational group-related alcohol deaths. Table. Alcohol Related Deaths in California, 1979-1981 Cirrhosis 5.5% Digestive organ cancers 5.7% Injuries 13.7% Suicide and homicide 5.% All other causes 64.9%

Zika and microcephaly Since May 2015, Brazil has experienced a significant outbreak of Zika virus. In recent years, Brazilian officials reported an increase in the number of babies born with microcephaly.

1. Briefly describe what we know and what we do not know about Zika virus.

2. What has been done and what should be done to prevent Zika virus epidemic in US and world-wide?

HMB342H1 Lecture Notes - Lecture 3: Cohort Study, Cumulative Incidence, Prevalence

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