epidemiology of screening

Question 1

what is a screening test ?

Answer 1

a test that is done among apparently well people to identify those at an increased risk of a disease or disorder

Question 2

what are the features of a screening test ?

Answer 2

screening :

1. done to apparently asymptomatic individuals
2. applied to a group of individuals
3. results are based on one criteria
4. results are not conclusive and less accurate

Question 3

what are the features of a diagnostic test ?

Answer 3

1. done to those with suggestive signs and symptoms
2. applied to a single person
3. results are based on evaluation of a number of symptoms, signs and investigations
4. results are conclusive

Question 4

what are the uses of screening programmes ?

Answer 4

case detection
control of diseases
research purposes

Question 5

what are the types of screening programmes ?

Answer 5

1. mass screenning

2. high risk or selective screening

Question 6

what is the difference between mass screening and high risk or selective screening ?

Answer 6

1. mass screening involves the whole population

2. high risk screening involves a selective group of the population

Question 7

what are the four indicies of screening test performance ?

Answer 7

sensitivity
specificity
positive predictive value
negative predictive value

Question 8

what does validity mean ?

Answer 8

how good is the screening test compared with the confirmatory diagnostic test
and how well does it measure what its supposed to measure
all the indicies of a screening test put together is the validity

Question 9

what is a gold standard test ?

Answer 9

a test has been generally accepted, at that moment, as the standard and the best method for definitive diagnosis of that disease

Question 10

what does sensitivity describe ?

Answer 10

the ability to identify correctly those who truly have the disease

Question 11

how is sensitivity calculated ?

Answer 11

true positives
___________
all diseases

all diseased is also = true positives + false negatives

Question 12

what is the formula for sensitivity ?

Answer 12

a
______. x 100
a + c

Question 13

what is specificity ?

Answer 13

the ability of the test to identify correctly those who dont have the disease

Question 14

how is specificity calculated ?

Answer 14

true disease negatives
___________________
all non diseased

Question 15

what is the formulae for specificity ?

Answer 15

d
_____x 100
b + d

Question 16

how is the overall validity calculated ?

Answer 16

true positives + true negatives
_______________________
grand total

Question 17

which values are used to address the probability of the disease ?

Answer 17

positive predicted value

negative predicted value

Question 18

what does the positive predictive value describe ?

Answer 18

the number of people with positive test results who actually have the disease

Question 19

how is the positive predicted value calculated ?

Answer 19

true disease positives 
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
all positives ( by the test)

Question 20

what is the predictive value a reflection off ?

Answer 20

the diagnostic power

Question 21

what are situations that require a test with high sensitivity ?

Answer 21

transfusion-donation safety

cancer

Question 22

how can the rate of false positive results be minimized ?

Answer 22

using a test with high specificity

Question 23

what is the relationship between positive and negative predicted values with the prevalence ?

Answer 23

PPV is directly proportional to the prevalence

NPV is inversely proportional to the prevalence

Question 24

what does reliability in a test mean ?

Answer 24

does the test produce the same result when repeated applications are made on the same individual

Question 25

what factors may affect the reliability of a test ?

Answer 25

intrasubject
intraobserver
interobserver

Question 26

what is the formula for the positive predictive value ?

Answer 26

a
_______ x 100
a + b

Question 27

how is the negative predictive value calculated ?

Answer 27

True disease Negative (TN)
___________________
All Negatives (by the test)

Question 28

what is the formula for the negative predictive value ?

Answer 28

d
____ x 100
c + d