Screening: lead time and length time

Question 1

describe lead time

Answer 1

• with screening you detect diseases earlier in TIME than if you wait till symptoms present
• lead time is the additional time that you know person has the disease, due to screening

Question 2

describe lead time bias

Answer 2

can look like increase in survival times

Question 3

describe length time

Answer 3

• with screening you detect diseases earlier in their PROGRESSION than if you wait til symptoms present
• length time is the decrease in severity o the disease due to screening

Question 4

describe length time bias

Answer 4

leads to overdiagnosis of less aggressive forms of the disease

Question 5

two consequences of length time bias

Answer 5

apparent increase in prevalence, due to screening
professionals will be compelled to treat the less severe disease, as its progression is unknown. however treatment can be harmful in itself (radiation therapy can cause cancers)