Following introduction of a screening program in a population, the mean survival time after diagnosis of breast cancer increased by 18 months.
The major problem in assessing the effectiveness of the program is:
Correct Answer B:
Lead time bias is the overestimation of survival duration among screen-detected cases when survival is measured from diagnosis. In the figure below (representing one patient) there is a 10 year survival at the point of the clinical diagnosis (old), but a 15 year survival from the early diagnosis (new). This is simply a reflection of earlier diagnosis, however, as the overall survival time of the patient is unchanged.
When a screening test identifies a cancer earlier, thereby increasing the time between diagnosis and death without prolonging life, this is called:
Lead-time bias is when a screening test identifies a cancer earlier, thereby increasing the time between diagnosis and death without actually prolonging life. Length-time bias is when a screening test finds a disproportionate number of cases of slowly progressive disease and misses the aggressive cases, thereby leading to an overestimate of the effectiveness of the screening. A false-positive test is one that suggests cancer where no cancer exists. The positive predictive value is the proportion of positive test results that are true positives. Attributable risk is the difference in risk of a disease that can be accounted for by a specific risk factor.
Lead-time bias is when a screening test identifies a cancer earlier, thereby increasing the time between diagnosis and death without actually prolonging life. Length-time bias is when a screening test finds a disproportionate number of cases of slowly progressive disease and misses the aggressive cases, thereby leading to an overestimate of the effectiveness of the screening. A false-positive test is one that suggests cancer when no cancer exists. The positive predictive value is the proportion of positive test results that are true positives. Attributable risk is the amount of difference in risk for a disease that can be accounted for by a specific risk factor.
A physician resident wished to determine the relationship between an ear infection in young children and parental history of the same infection. From the records of a large pediatric practice, he identified 100 children between one and three years of age who had experienced at least three ear infections in the past year. 100 children in the same age group, treated by the same practice for other illnesses, were also identified. The physician interviewed the parents of subjects in both groups to determine their history of the target illness as young children.
Which of the following study types is being used by this physician?
Correct Answer C:
A case control study is a study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called a retrospective study.
A total of 10,000 Vietnam veterans, with and without cancer were asked to give a history of their exposure to Agent Orange.
This scenario best illustrates which one of the following?
A case-control study is a study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). Researchers study the medical and lifestyle histories of the people in each group to learn what factors may be associated with the disease or condition. For example, one group may have been exposed to a particular substance that the other was not. Also called a retrospective study.
[A retrospective study looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is established at the start of the study. Case-Control studies are usually but not exclusively retrospective, the opposite is true for cohort studies.]
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