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Paeds Exam Cram > Statistics > Flashcards

Statistics Flashcards

1
Q

Systematic review/meta analysis

A

Most reliable

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2
Q

Randomised control trial

A

Least biased due to randomisation
Can prove causality
Intervention versus placebo

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3
Q

Cohort studies

A

Observational. Association not causality
Exposure versus no exposure
Prospective or retrospective
Relative risk >3

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4
Q

Case control studies

A 
Observational. Association not causality
Disease versus no disease
Good for rare diseases
Can do with small numbers
Most biased
Odds ratio >4
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5
Q

Cross sectional

A

Frequency of disease and risk factors at a particular point in time
Risk factor association not causality
Prevalence

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6
Q

Forest plot

A

Size of square - weight given to the study

Placement of square - mean effect of the intervention (ODDS RATIO)

Horizontal lines - size of the CI (narrower = more precise)

Diamond - meta analysis findings (overall result)

Edges of diamond = CI

if the edges of the diamond crosses the vertical line = NOT statistically significant

if p <0.05 then statistically significant

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7
Q

Clinical trials - phase 1

A

SMALL number, HEALTHY

Is it safe? SAFETY, TOXICITY, pharmacokinetics

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8
Q

Clinical trials - phase 2

A

SMALL number, with the DISEASE

Treatment EFFICACY, optimal DOSING, adverse effects

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9
Q

Clinical trials - phase 3

A

LARGE number, RCT, randomly assigned to treatment under investigation or placebo/best available treatment
Compares new to current/no treatment. SAFETY compared to gold standard, SIDE EFFECTS
EFFICACY of experimental therapy, compare to other treatments

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10
Q

Clinical trials - phase 4

A

Post marketing SURVEILLANCE of patients after treatment is approved
Detects rare or long term side effects

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11
Q

Prevalence

A

All cases = # existing cases/ total # people in population

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12
Q

Incidence

A

New cases = # new cases / # people at risk

Incidence down = PPV down

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13
Q

Normal distribution

A

1 SD = 68%
2 SD = 95%
3 SD = 99.7%

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14
Q

Confidence interval

A

95% CI = p 0.05
If 95% CI includes 1 - NOT statistically significant
CI between 2 groups overlaps - NOT statistically significant
CI between 2 groups don’t overlap - statistically significant difference

Narrower the CI = more precise (less likely due to chance)

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15
Q

Sensitivity Specificity

A

Screening test - sensitivity **
Sensitivity and specificity are independent of prevalence
Prevalence same as PPV but opposite to NPV

(Incidence ~ Prevalence ~ Pretest Probability ~ Positive Predictive Value)

High sensitivity = less false negatives therefore miss less people
POS for disease correctly tests POS

High specificity = less false positives
NEG for disease correctly tests NEG

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16
Q

Positive likelihood ratio

A

Probability of a positive test in a person with the disease compared to a person without disease

= SENSITIVITY / (1 - SPECIFICITY)

17
Q

Negative likelihood ratio

A

Probability of a negative test in a person with disease compared to a person without disease

= (1 - SENSITIVITY) / SPECIFICITY

18
Q

Absolute Risk

A

Rate of occurrence of a disease (incidence in exposed)

19
Q

Absolute risk reduction

A

= CONTROL EVENT RATE - EXPERIMENTAL EVENT RATE

20
Q

Number needed to treat

A

How many patients need to be treated to prevent one event

= (1/ARR) x 100

21
Q

Relative risk

A

RCT/cohort studies

Incidence rate in exposed / Incidence rate if not exposed

RR = 1 then risk A = risk B
RR >1 INCREASED risk of outcome in exposed person
RR <1 REDUCED risk of outcome in exposed person

RCT small RR, cohort RR >3, case control RR >4

e. g. RR 1.36 = risk DISEASE is INCREASED by 36%
e. g. RR 0.8 = risk DISEASE is reduced by 20%

22
Q

Relative risk reduction

A

Population of the baseline risk which was reduced by a given intervention

Absolute risk reduction / Control event rate

e.f. RR 0.39 therefore 61% less likely to get disease

But if baseline population is 20% then what is the likelihood?

61% less than 20%. ~60% of 20% = 12%
So 20-12 = 8. 8% risk of Dx or 0.2 x 0.39 = 0.078 ~8%

23
Q

Odds ratio

A

Case control study

Odds of EXPOSURE in those WITH DISEASE /
Odds of EXPOSURE in those WITHOUT DISEASE

OR = 1 No change in frequency of exposure
OR <1 decreased frequency of exposure among cases
OR >1 increased frequency of exposure among cases

24
Q

Hazard ratio

A

Probability that individual at time t has an event at that time
Similar to RR but takes time into account

HAZARD IN TREATMENT ARM /
HAZARD IN CONTROL ARM

25
Q

Null hypothesis

A

No difference between the same or population being compared, differences due to random variation

26
Q

Type 1 error

A

Picking up significant difference when there ISN’T one
Risk of FALSE POSITIVE result
Reduces with randomising, blinding

27
Q

Type 2 error

A

MISS a difference when there actually is one
Risk of FALSE NEGATIVE
REDUCES with LARGER sample size***

Paeds Exam Cram (19 decks)

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