Show:
Validity
Predictive Value
Reliability of Tests
Disease X
Screening Programs
100
The ability of a test to distinguish between who has a disease and who does not.
What is validity?
100
If the test results are positive in a patient, what is the probability that this patient has the disease?
What is positive predictive value
100
What occurs when there is variation between two or more readings of the same test results made by the same observer?
What is intraobserver variation
100
A new screening program was instituted in England. The program was a screening test that is effective in detecting cancer X at an early stage. Assume there is no effective treatment for this type of cancer. Assume that the rates are calculated from all known cases of cancer X. What will happen to the incidence rate of cancer X during the first year of the screening program?
What is increased incidence rate?
100
The best index for concluding that an early detection program for breast cancer truly improves the natural history of disease, 15 years later would be: a.) A smaller proportionate mortality for breast cancer 15 years after its intitiation of early detection program compared to the proportionate moratlity prior to its initiation b.) Improved long-term survival rates for breast cancer patients c.) A drecrease in the incidence of breast cancer d.) A decrease in the prevalence of breast cancer e.) None of the above
What is b?
200
The ability of the test to identify correctly those who have the disease.
What is sensitivity?
200
If the test result is negative, what is the probability that the patient does not have the disease?
What is negative predictive value
200
What measures the extent to which the observed agreement exceeds that which would be expected by chance alone?
What is kappa statistic
200
A new screening program was instituted in England. The program was a screening test that is effective in detecting cancer X at an early stage. Assume there is no effective treatment for this type of cancer. Assume that the rates are calculated from all known cases of cancer X. What will happen to the prevalence rate of cancer X during the first year of the screening program?
What is increased prevalence rate?
200
In general screening should be undertaken for the diseases with the following feature(s): a.) Diseases with a low prevelance in indentifiable subgroups of the population? b.) Diseases for which the case-fatality rates are low c.) Diseases with a natural history that can be altered by medical intervention d.) Diseases that are readily diagnosed and for which treatment efficacy has been shown to be equivocal in evidence from a number of clinical trials e.) None of the above
What is c?
300
The ability of the test to identify correctly those who do not have the disease.
What is specificity?
300
1,000 people are screened and 200 of them have positive tests. Of these 200 people, 90 have the disease. What is the positive predictive value?
What is 90/200 or 44%
300
What is variation between observers?
What is interobserver variation
300
A new screening program was instituted in England. The program was a screening test that is effective in detecting cancer X at an early stage. Assume there is no effective treatment for this type of cancer. Assume that the rates are calculated from all known cases of cancer X.
What is decreased case fatality rate?
300
Which of the following is not a possible outcome measure that could be used as an indicator of the benefit of screening programs aimed at early detection of disease? a.) Reduction of case-fatality rate in screened individuals b.) Reduction of mortality in population screened c.) Reduction of incidence in the population screened d.) Reduction of complications e.) Improvement in the quality of life in screened individuals.
What is c?
400
A physical examination was used to screen for high blood pressure in 1000 men. 100 have tested positive, and 900 have tested negative. Of the 100 positives, 80 have been correctly identified. Of the negatives, 800 have been correctly identified. What is the sensitivity of this test?What is the specifity of this test?
Sensitivity: (80/100)=80% Specificity: (800/900)=79%
400
A screening test is used in the same way in two similar populations, but the proportion of false positive results in population A is lower than population B. What is the likely explanation for this finding?
What is the prevalence of disease is higher in population A
400
What is variation in results for the same individual?
What is intrasubject variation
400
A new screening program was instituted in England. The program was a screening test that is effective in detecting cancer X at an early stage. Assume there is no effective treatment for this type of cancer. Assume that the rates are calculated from all known cases of cancer X. What will happen to the mortality rate of cancer X during the first year of the screening program?
What is mortality rate remaining constant?
400
Give an example of a type of selection bias that can occur in a study designed to evaluate the benefits of screening?
What is referral bias (volunteer bias) or what is length-biased sampling (prognostic selection)?
500
What happens when two sequential tests are used and those who test positive by the first test are brought in for the second test?
There is a net loss in sensitivity, but a net gain in specificity, compared with either test alone.
500
A physical examination was used to screen for breast cancer in 2,500 women with biopsy-proven adenocarcinoma of the breast. There were also 2,500 women who showed no evidence of cancer at biopsy who acted as the control group. The results of the physical examination were positive in 1,800 cases and in 800 control women. What was the positive predictive value of the physical examination?
What is 1800/2600 or 69.2%
500
Abnormal Normal Total Abnormal 40 20 60 Normal 10 30 40 Total 50 50 100 What is the percent agreement between the two physicians?
What is 70%
500
What outcome measures of screening programs does the screening program does Cancer X meet?
What is reduction of case-fatality rate in screened individuals? What is increase in percent of cases detected at earlier stages?
500
Assume early detection of disease X thorugh screening improves prognosis. At which point in the natural history of disease X would a screening program be most effective?
What is betwen biologic onset of disease and earliest possible detection of disease by any screening technique?