REVISION GUIDE: CRITICAL NUMBERS Flashcards Preview

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Flashcards in REVISION GUIDE: CRITICAL NUMBERS Deck (34)
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1

what is prevalence probability?

probability of having a disease at a given point in time

2

what is incidence probability?

probability of getting a disease during a specified point in time

3

what is the incidence rate?

average rate of change over time

4

what is the hazard rate?

the instantaneous rate of change

5

what are the 2 equations that can be used to calculate probability?

p = no. favourable outcomes / all possible outcomes
p = no. of cases / total population

6

what is conditional probability?

the probability that something will happen, given an event has already happened

7

how would you calculate odds ratio?

odds = cases / non-cases

8

what are the ranges for probability and odds ratios?

probability = 0-1
odds = 0 to infinity
- more than 1 = positive association
- 1 = no association

9

what are the problems with prevalence probability?

- length-time bias - conditions with a longer duration are more likely to be captured in prevalence
- a difference in prevalence can simply indicate shorter/longer average duration of disease or a different treatment success

10

what are the problems with incidence probability?

- issues with competing risk - ie death due to another cause
- ignores time to event

11

how can you avoid problems with incidence probability?

use incidence rate instead

12

how would you calculate absolute risk difference?
drug A = 0.6 drug B = 0.2

absolute risk difference = A - B
= 0.6 - 0.2
= 0.4 = 40%

13

how would you calculate risk ratio?
drug A = 0.6 drug B = 0.2

risk ratio = A / B
= 0.6 / 0.2
= 3

14

how would you calculate relative risk difference?
drug A = 0.6 drug B = 0.2

relative risk difference = (A - B / B) x 100
= (0.6 - 0.2 / 0.2) x 100
= (0.4 / 0.2) x 100
= 2 x 100 = 200%

15

what is relative risk?

exaggerates risk
they do not indicate a baseline

16

what is risk difference?

gives an absolute measure of the association of exposure on disease occurrence
gives a clearer sense of public health impact

17

what is risk ratio?

gives a relative measure
give a clearer sense of strength of effect

18

what is the definition of number of people needed to treat/harm?

it is the number of people you need to treat in order to prevent one outcome
it indicates the potential benefit of a clinical intervention

19

how do you calculate the number of people needed to treat/harm?

NNT = 1 / Risk Difference

20

what is a cohort study?

- forward prospective study
- population-based
- onset of study -> follow-up

21

what are the strengths of a cohort study?

- useful for demonstrating causal effects
- multiple diseases can be studies
- multiple exposures can be studied

22

what are the weaknesses of cohort studies?

- expensive and time consuming
- not suitable to rare diseases
- need to deal with confounding factors

23

what are cross-sectional studies?

- investigates what is happening at a certain point in time
- outcome and exposures are measured simultaneously

24

what are the strengths of cross-sectional studies?

- relatively fast and inexpensive
- rapid feedback on current events
- multiple outcomes and exposures can be studied

25

what are the weaknesses of cross-sectional studies?

- not suitable for rare diseases
- very limited potential to establish disease aetiology
- can be affected by selection bias and confounding factors

26

what are case-control studies?

- retrospective - past exposures are measured
- sample is taken based on a disease

27

what are the strengths of case-control studies?

- quick and inexpensive
- suitable for rare diseases
- multiple exposures can be studied
- suitable for transient exposures eg outbreaks

28

what are the weaknesses of case-control studies?

- only a single disease can be studied
- not suitable for rare exposures
- exposure data needed before start of study
- can be affected by selection bias and confounding factors

29

what are randomised control trials (RCTs)?

- have an entry criteria and split randomly into groups
- this prevents confounding problems
- trials can be double blinded
- prevents bias

30

what are the strengths of RCTs?

- they give the most convincing evidence for cause and effect
- gold standard for evaluating interventions