Question

Question 16 

Which of the following best describes a lead-time bias? 

Slow-progressing cases of disease with a better prognosis are more likely to be identified than faster-progressing cases of disease with a poorer prognosis 

Screening advances the time of diagnosis, making it difficult to evaluate survival 

Occurs when screening identifies an illness that would not have shown clinical signs before a person's death from other causes 

When the choice of study participants is healthier than the general population, making screening look good 

None of the answers listed 

Question 17 

Consider the following hypothetical findings on the evaluation of a screening test for tuberculosis 

- 40 diseased and positive individuals, 

- 15 diseased and negative individuals 

- 75 not diseased and positive individuals, 

- 1,600 not diseased and negative individuals. 

How would you interpret the specificity of the screening test for tuberculosis? 

About 99% of people without tuberculosis tested negative 

Approximately 99% of the people tested did not have tuberculosis 

Among people without tuberculosis, almost 96% tested negative 

Among people who tested negative, almost 96% did not have tuberculosis 

None of the answers listed 

Answer 1

16)option b, lead time bias it is the screening is intended to improve the prognosis of diagnosed cases , screening is particularly important for chronic disease in which there is a high prevalence of individuals in the presymptomatic phase of the disease however because screening advances the time of diagnosis it may be difficult to evaluate the benefits of early treatment in other words the difference in time between the date of diagnosis with screening and the date of diagnosis without screening is called lead time if lead time is counted in the survival time of patients it will give a misleading picture of the benefits of treatment this inflation of survivial is called lead time bias. 17) option a, , specificity is the proportion of subjects without the disease who have a negative test and specificty is the ability to correctly identified those without disease.