PUBHLTH 144 Lecture Notes - Lecture 5: Net Present Value, Unimodality, Multimodal Distribution

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13 Oct 2016

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Definition ability to distinguish between those who have the disease and those who do not. 2 components: sensitivity proportion of truly disease persons who are identified as diseased by the screening test. True positive rate: specificity proportion of truly non-diseased persons who are identified as non-diseased by the screening test. In order to evaluate the validity of a clinical test (sensitivity and specificity), a golden standard for diagnosis is required. Golden standards are definitive and often highly invasive. For assessing the measured of validity, individuals must be administered both the gold standard and screening test: remember: for screening the population, we are not assessing the validity; we only know those who test positive and negative. Tests with dichotomous variables: tests with dichotomous variables have only 2 categorical states, positive or negative (i. e. hiv infection) Step 1: conduct a less expensive or less invasive test. Step 2: conduct a 2nd test among those who tested positive: example: immunoassays for hiv testing.

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)A screening test is available to identify individuals with a genetic mutation that puts them at greater risk for stroke. The test is extremely expensive and is not covered by most insurance plans, so those choosing to have the test usually have to pay for it out-of-pocket. However, it has been determined that the screening test is very valuable because the annual incidence of stroke among those who have been screened is nearly half that of the general population. 7) One major benefit of mammography screening for breast cancer is that the disease is often diagnosed in the presymptomatic phase of the disease, before it is detectable by any other means, and breast cancers diagnosed in such early stages respond better to treatment. Another benefit of screening is that women diagnosed with breast cancer by way of mammography have better survival rates than women diagnosed by other means. 8) The prognosis for neuroblastoma, a tumor that occurs in young children, varies greatly by patient. Some tumors are slow-growing and may even heal spontaneously. Others tumors are fast-growing and aggressive. A urine screening test for neuroblastoma is currently available that detects metabolites produced by the tumor. It has been suggested that such screening is highly valuable PH20001 Essentials of Epidemiology 2 because the case-fatality rate of neuroblastoma among children diagnosed with the urine test is much lower than it is for those who were not screened. 9) Suppose that a new screening test has recently been developed to aid in the early identification of individuals with rheumatoid arthritis. However, the value of the test has not yet been established. In an effort to test the effectiveness of the new test in predicting a future diagnosis of rheumatoid arthritis, investigators enroll a group of volunteer participants, record their test result, and follow them forward for the development of the condition. It is subsequently determined that the new screening test is highly effective in predicting a definitive diagnosis of rheumatoid arthritis because the incidence of the condition among those who screened positive was much higher than that of the general population. 10) There are at least a dozen types of human papillomaviruses (HPV) that are considered high-risk and cause approximately 5% of all cancers world-wide. However, high-risk HPV infections are common and most occur without any symptoms and resolve on their own within 1-2 years. In 2003, cervical HPV screening tests became available and are now approved for use in combination with a Pap test among women over the age of 30. Such tests can detect infection of several high-risk HPV types before cell changes become evident. Some argue that HPV screening tests should be approved for universal use among women of all ages because the incidence of high-risk HPV infections has increased dramatically over the past decade. Identify the bias being described in the scenario

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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

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?

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

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

PUBHLTH 144 Lecture Notes - Lecture 5: Net Present Value, Unimodality, Multimodal Distribution

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