Lecture 26: Screening; A Special Type Of Prevention Strategy Flashcards Preview

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Flashcards in Lecture 26: Screening; A Special Type Of Prevention Strategy Deck (47)
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1

What is an example for primary prevention screening?

Screening women for alcohol intake to prevent breast cancer

2

What is an example of secondary prevention screening?

Breast cancer screening (detects early stage of disease and aims to prevent more serious disease

3

What is the screening test like?

Less expensive, less invasive (so effective on large population)

4

What's the diagnostic test like?

It's called a gold standard
Often invasive
Expensive
Impractical for large populations

5

What happens after the gold standard diagnostic test?

Disease positive get the intervention or treatment
Disease negative get rescreened after a specific period

6

What happens to test negative after first screen?

They get rescreened after a specific period

7

What are the 4 screening criterion?

1. Suitable disease
2. Suitable test
3. Suitable treatment
4. Suitable screening time

8

Two features of a suitable disease?

1. An important public health problem
2. Knowledge of the natural history of the disease (or relationship of risk factors to the condition)

9

Is a suitable disease common or uncommon?

It can be either- if it's effective and easy, uncommon screenings can occur (eg babies screened for pku)

10

Why do we screen for uncommon disease too?

Because if we have an early detection and intervention we can get a better outcome

11

Why is knowledge of the disease important for screening?

So we know it's detectable early with a detectable risk factor/disease market and needs an increased duration of preclinical phase (after biological onset, before clinical diagnosis)

12

Examples of screening?

Breast cancer, cervical cancer, diabetes

13

What are the key aspects of a suitable test?

1. Reliable
2. Safe
3. Acceptable
4. Simple
5. Cheap
6. Accuracy

14

What is accuracy?

The ability of a test to indicate which individuals have the disease and which don't

15

Two measures of accuracy?

Specificity
Sensitivity

16

What two types of tests are used?

Screening test
Gold standard test

17

What is the gold standard?

Is in effect the ideal diagnostic test (example: colonoscopy). Is expensive and invasive

18

What is a general screening test?

(A less expensive diagnostic test) eg faecal occult blood test (for colon cancer)

19

Describe the gate frame screening SQUARE

Top left: true positive
Bottom left: false negatives
Top right: false positives
Bottom right: true negatives

20

What is sensitivity?

The ability to identify correctly those who have the disease (a) from all individuals who have the disease (a+c)

The likelihood of a positive test in those with the disease

21

What is specificity?

The ability of the test to identify correctly those who do not have the disease (d) from all individuals who don't have the disease (b+d)

22

Sensitivity calculation?

True positives/all with disease x100

A/(a+c) x100

"X% of those with the disease will test positive in the new test"

23

Specificity calculation?

True negatives/all without the disease
= b/(b+d) x 100

"X% of those without the disease will have a negative result in the new test"

24

How do we evaluate test accuracy?

- the sensitivity is high if the proportion of true positives are high
- the specificity is high if the number of true negative are high

25

What are the fixed characteristics of a new test?

Sensitivity and specificity

26

What are the two predictive values?

Positive predictive value
(PPV)
Negative predictive value (NPV)

27

Why are sensitivity and specificity different between populations?

Because the prevalence of disease is different in different populations

28

So what is a predictive value?

How well a new screening test works in a specific population

29

What does the positive predictive value measure?

Out of everyone who tests positive (false and true), how many truly have the disease?

Or the probability of having disease if the test is positive

30

Calculation for the positive predictive value?

True positives/all who test positive x100

Or

A/(a+b) x100