POPM 3240 Lecture Notes - Lecture 14: Rare Disease, Odds Ratio, Relative Risk

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27 Mar 2018

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Can do it only in the exposed group. Do both exposed and not exposed in the population. Relative risk = (risk of disease in exposed group) / (risk of disease in non-exposed group) This is a ratio, meaning that the numerator is a part of the denominator. Risk in e+ = a / (a+b) Risk in e- = c / (c+d) Rr = p(d+|e+) / p(d+|e-) = [a / (a+b)] / [c / (c+d)] Rr = 2 means that the risk of disease in the exposed group is two times the risk of disease in non-exposed group i. e. not significant. The exposed are 2x as likely to be diseased as non-exposed. If rr=1, that means there is no association between the e and o. If rr > 1 , positive association between e and o. If rr < 1 , negative association between e and o. For example rr = 0. 25, e is flu vaccine, o is influenza.

Related Questions

Compute the Person-Years of smoking exposure using the tablebelow. (Hint: add the years at risk of throat cancer (TC) â seeexamples).
Once they develop TC they are no longer at risk and their yearsin the study canât be counted.
Add each personâs years of exposure in the right column andenter the value in the box next to âTotal P-Y at Risk of ThroatCancerâ.
Then count the P-Y at risk for the Current/Former Smokers(exposed) and the P-Y at risk for the Never-Smokers (notexposed)
Using the Person-Years for each exposure group as thedenominator and the number of TC recorded for each exposure group;compute the Incidence Density for TC risk in current/former smokers(exposed) (ID_E) & compute the incidence density forTC risk in never smokers (not exposed) (ID_NE).
The compute the Incidence Density Ratio (also call RR), dividethe ID_Eby the ID_NE. This value is interpretedthe same as the Relative Risk.

		Years in the Study at Risk of Developing ThroatCancer								Years at Risk
Person	Smoker	1	2	3	4	5	6	7	8	Years at Risk
A	Yes	at risk	at risk	TC	No longer at risk of throat cancer					2
B	No	at risk	at risk	at risk	at risk	at risk	at risk	at risk	at risk	8
C	No
D	Yes						TC
E	Yes				TC
F	No
G	No					TC
H	No								TC
I	Yes		TC
J	Yes							TC
	Total P-Y at Risk of Throat Cancer

Sum the Person-Years of Exposure for each exposure group? (1point)

Former/Current Smoker (1/2 point)

Never Smoker(1/2 point)

How many of the exposed & not exposed participantsdeveloped throat cancer (1 point)?

Former/Current Smoker (1/2point):

Never Smoker(1/2point):

What is the Incidence Density for the exposed (ID_E)and non-exposed (ID_NE) groups? (1 point)

Former/Current Smoker (1/2point):

Never Smoker (1/2 point):

Compute the Incidence Density Ratio (IDR). Is the IDRprotective or hazardous? (1 point).

10. Using the interpretation for Relative Risk onpage 120 of your text, interpret the meaning of the IncidenceDensity Ratio (1 pt):

rubyjellyfish692

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

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

POPM 3240 Lecture Notes - Lecture 14: Rare Disease, Odds Ratio, Relative Risk

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