Lecture 5 Screening

Question 1

What is primary prevention?

Answer 1

Prevents the onset of disease, which may be accomplished through the removal of a risk factor

Question 2

What is secondary prevention?

Answer 2

Reduce the impact of a disease that may or may not be a asymptomatic

Question 3

What is tertiary prevention?

Answer 3

Reduction or prevention of health deterioration once disease is present

Question 4

Define Screening

Answer 4

The practice of investigation apparently healthy individuals with the object of detecting unrecognised disease or its precursors in order that measures can be taken to prevent or delay the development of disease or improve prognosis

Question 5

What is a diagnostic test?

Answer 5

Is used to determine the presence or absence of a disease when a subject shows signs or symptoms of the disease

Question 6

When is the Detectable pre-clinical phase?

Answer 6

The time interval between possible detection by screening and later detection after symptoms

Question 7

What is the pre-clinical phase in screening?

Answer 7

The time between the Biological Onset and the when Symptoms develop

Question 8

What is the clinical phase in screening?

Answer 8

The time between when Symptoms develop and Death(outcome) occurs

Question 9

Why is Screening useful?

Answer 9

Early diagnosis of disease where early intervention improves prognosis

Identification of high risk individuals where intervention improves prognosis

Identification of those posing a risk to others

Question 10

What are the different approaches to Screening?

Answer 10

Mass
Targeted
Systematic
Opportunistic

Question 11

What is Mass approach in screening?

Answer 11

Applies to whole population (usually defines by age or gender)

Question 12

What is the Targeted approach in screening?

Answer 12

Select sub groups though to be at increased risk

Example: TB contacts

Question 13

What is the Systematic approach in Screening?

Answer 13

The population is called for screening using a register

Example: Brest cancer, cervical cancer:

Question 14

What Is the Opportunistic approach in Screening?

Answer 14

The population is approached when they make contact for another reason

Example: HIV in GUM clinics

Question 15

What are the disadvantages of Screening?

Answer 15

Where delaying treatment is no less effective than early treatment

When the prevalence of the condition is low

When the screening test is not accurate

Question 16

What are the characteristics of a good Screening test?

Answer 16

Inexpensive 
Easy to administer 
Minimal discomfort 
Reliable (consistent outcome)
Valid (distinguished diseased & non-diseased people )

Question 17

What are the sources of unreliability (inconsistency)?

Answer 17

Biological variability
Instrument variability
Inter-observer variation

Question 18

What determines the validity of a test?

Answer 18

Sensitivity & specificity

Question 19

What is Sensitivity?

Answer 19

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

Question 20

What is specificity?

Answer 20

The ability of the test to identify correctly those who do not have the disease

Question 21

What is the formula for Sensitivity?

Answer 21

Sensitivity= True Positive/ (True Positive + False Negative)
X 100 for percentage probability
(Left column in contingency table)

Question 22

What is the formula for Specificity?

Answer 22

Specificity= True Negative/ (True Negative + False Positive)

X100 for percentage of probability

(Right column in contingency table)

Question 23

Define Positive predictive value (PPV)

Answer 23

The proportion of patients who test positive who actually have the disease

TRUE POSITIVES

Question 24

Define Negative predictive value (NPV)

Answer 24

The proportion of patients who test negative who are actually free of the disease
(DO NOT HAVE DISEASE)

TRUE NEGATIVES

Question 25

What is the formula for Positive Predictive Value (PPV)?

Answer 25

PPV=True Positive/ (True Positive + False positive)

FIRST ROW IN CONTINGENCY TABLE

Question 26

What is the formula for Negative Predictive value (NOV)?

Answer 26

NPV= True Negative/(True Negative+ False Negative)

SECOND ROW IN CONTINGENCY TABLE

Question 27

What do Predictive values depend on?

Answer 27

The prevalence within the given population

Question 28

What are the two main cons of Screening?

Answer 28

False positives , people who test positive even if they don’t have the disease

False negative, people who test negative but the do have the disease

Question 29

What are the factors that influence screening?

Answer 29

Referral/Volunteer Bias

Selection Bias