Critical Appraisal Flashcards

1
Q

List the hierarchy of research design

A
RCT double blind
> Randomized Controlled Studies
> Cohort Studies
> Case Control Studies
> Case Series
> Case Reports
> Ideas, editorials, opinions
 > Animal research
> In vitro ('test tube') research
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2
Q

RCT considered ‘best’ study design to confer causality b/c of:

A

Cofounders assigned equally to all groups.

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3
Q

How do you assess exposure status:

Case control, Cohort or RCT?

A

Case control

  • you start w/ the outcome (dx) and assess exposure status
  • less time, good for rare dx
  • less$ but introduces bias
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4
Q

What is a strength of the cohort design? Con?

A

start w/ exposure (exposed vs. unexposed)
assess outcome over time

(+): Tx not withheld , compare risks/rate in both groups
(-): introduce bias, time, expense

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5
Q

What is the “gold standard” in research design?

A

RCT

- assign to groups randomly and compare rates of outcomes

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6
Q

Pro and Con of RCT:

A

(+)

  • best evidence for causality
  • minimize cofounder
  • greater chance of blinding

(-)

  • $$/ time consuming
  • difficult for rare events
  • may be unethical
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7
Q

How do you calculate relative risk?

A

Incidence (intervention group)/ incidence (control)

RR> 1= incidence higher in tx group
RR= no difference
RR< 1= incidence lower in tx group

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8
Q

Does the course help pass the exam. 2/20 fail in PR. 10/20 if cooking. Calculate relative risk?

A

incidence intervention= 2/10= 0.1

Incidence control= 0.5

0.1/0.5= 0.2

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9
Q

Relative risk reduction (RRR)

A

1- RR

‘attending the course decreases relative risk by failing by x.’

If RR= 0.2
1-0.2= 0.8
80%.

Course decreases relative risk of failing by 80%

AKA how many times intervention or exposure increase/decrease risk of outcome.

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10
Q

Number needed to treat=

A

NNT= inverse of ARR

ARR= Incidence in Control - Incidence in Intervention

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11
Q

Absolute risk reduction (Risk Difference)

A

Difference in incidence between tx and control

ARR= Incidence in Control - Incidence in Intervention
= Or risk of control x RRR

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12
Q

New drug. Ad states drug decreases failure rate by 25%. Baseline failure rate in control 40%. How many needed to tx to prevent one failure.

A

NNT= inverse of ARR

ARR= risk of control x RRR

ARR= 0.4 x 0.25 = 0.1
NNT= 1/0.1= 10
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13
Q

Explain what RR, RRR, ARR are.

A

RR= incidence higher or lower in intervention after tx= DIVIDE incidence (intervention/control)

RRR= doing tx reduces relative risk by %.= 1- RRR

ARR= diff in risk btwn tx and control = SUBTRACT incidence (control- intervention)

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14
Q

New drug. Ad states drug decreases failure rate by 25%. Baseline failure rate in control 40%. What is the 25% and what is the 40%?

A

40%= risk in control group.

RRR= 25%

ARR= risk control x RRR

NNT= 1/ ARR

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15
Q

Which is adv. of case control study over cohort?

  • retrospective
  • ideal for short lag btwn exposure and outcome
  • accurately estimate RR
  • ideal for rare dx/outcome
A

Ideal for rare dx/ outcomes

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16
Q

List two pro and con of cohort study:

A

Pro:

  • tx not withheld
  • generally cheaper than RCT
  • can estimate RR (incidence)

Con:

  • control hard to get
  • does not deal with anticipated cofounders
  • blinding more a challenge
  • $$
  • challenge for rare dx
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17
Q

T or F: Case control is the reverse of Cohort studies?

A

True.

  • Start with group based on OUTCOME and then go back in the to look at historical rates of exposure
  • can match potential cofounders
  • give ODDS RATIO
18
Q

List (+) and (-) of case control design?

A

Pro:

  • cheap, quick
  • good for RARE dx or long-lag from exposure to outcome

Con:

  • recall bias
  • choice of control can be issue
  • does not deal w/ anticipated cofounders
  • can’t tell prevalence
  • no RR or incidence
19
Q

You are studying population of 100 people of which 30 have dx. What is the incidence?

A

Don’t know.

But can say prevalence is 30%

20
Q

Define sensitivity + specificity=

A

SNOUT

  • SeNsivity high
  • Negative test
  • rule OUT dx

i.e CX for UTI

SPIN

  • Specificity high
  • Positive test
  • rules IN dx

i.e. bx CA

** remember columns!

21
Q

Write are the equations for sensitivity and specificity?

A

THINK COLUMN OF TABLE

Sensitivity
= True +/ (True+ and False (-))

Specificity = True (-) / True (-) + False (+)

22
Q

Define positive and negative productive value.

A

(+) Predictive value= if test positive likely dx presents.

(-) predictive value= if test negative, likely dx absent

23
Q

T or F: (+) and (-) predictive values vary with prevalence.

A

True.

Versus . SNOUT and SPIN do not .

24
Q

What are the equations for positive and negative predictive value?

A

THE ROWS!

PPV= True positive/ (true positive + false positive)

Negative PV= true negative/ (true neg. + false negative)

25
Define Null hypothesis
no difference between groups being compared.
26
Define P value
= probability that difference in observed study simply due to chance (type 1 error)
27
Define Type 2 Errors
based on 'true difference' what is chance difference not statistically significant
28
Define Power
1- type 2 errors | = what's the strength that I have to find differences in our study
29
How do you critically appraise an article?
Results Valid - trial address focused issue - design consistent w/ question (i.e. RCT if want cause-effect, versus rare dx case-cohort) - i.e. blinded well versus cases recruited well - cofounders considered What are Results - measure really measure what they should (i.e. imperfect proxy) - how large is the effect - how precise (p interval, confidence interval) Will they help = External validity - help locally? - can study be generalized?
30
What is an RCT
randomized control trials exposure assigned randomly to group and followed over time for outcomes
31
What are experimental design and what are observational:
RCT= experiment Rest= Observation - Cohort - Case-control - Cross-sectional etc.
32
Cross sectional study IS?
design that examine pop'n at ONE point in time. - selected w/out exposure or dx status in mind - measure dx prevalence
33
What is a systematic review? Versus Meta-Analysis
Systematic = literature reviewed prepared using systematic approach to minimize bias and random error - ID and critique relevant research studies - discuss factors that may explain heterogeneity - synthesize info - May or may not include meta-analysis Meta-analysis: - statistical pooling of results of individual studies via defined protocol - statistic goal to produce signal estimate of tx effect
34
Study with minimal bias. Cofounder distributed unbiased. Can do cause-effect. =
RCT
35
Can study multiple outcome for one exposure. Can look at DIRECTION of cause of effect.
Cohort
36
Good for studying rare dx. Can examine multiple exposures. Cost effective.
Case-Control
37
Best for getting prevalence of disease or risk factor. Cheap and simple.
Cross-sectional survey = relationship btwn dx (and other traits) as exist in defined pop'n at ONE point in time.
38
The specificity of a screening test best described as proportion of person: - condition who test (+) - condition who test (-) - without condition who test (+) - without condition who test (-)
Without condition who test negative. **alway think it's opposite of (+) predictive value.
39
On the true positive and true negative table- what row and column is what?
True positive= PPV row; Sensitivity Column | True negative= (-) PV row; Specificity Column
40
100 patients screened for colon CA. 30 (+) screen. 5 found to have colon cancer. What is positive predictive value:
True positive/ True positive + false positive = 5/30 = 16.6%
41
If newborn screen TOO sensitive - unacceptable # of: - false (-) - false (+) - inconclusive test - true (+) - true (-)
False (+) test
42
T or F: (+) screen is dx for condition
False. Require dx testing.