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RC: Specialties Woo Hoo > Critical Appraisal > Flashcards

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
Q

Define Null hypothesis

A

no difference between groups being compared.

26
Q

Define P value

A

= probability that difference in observed study simply due to chance (type 1 error)

27
Q

Define Type 2 Errors

A

based on ‘true difference’ what is chance difference not statistically significant

28
Q

Define Power

A

1- type 2 errors

= what’s the strength that I have to find differences in our study

29
Q

How do you critically appraise an article?

A

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
Q

What is an RCT

A

randomized control trials exposure assigned randomly to group and followed over time for outcomes

31
Q

What are experimental design and what are observational:

A

RCT= experiment

Rest= Observation

  • Cohort
  • Case-control
  • Cross-sectional etc.
32
Q

Cross sectional study IS?

A

design that examine pop’n at ONE point in time.

  • selected w/out exposure or dx status in mind
  • measure dx prevalence
33
Q

What is a systematic review? Versus Meta-Analysis

A

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
Q

Study with minimal bias. Cofounder distributed unbiased. Can do cause-effect. =

A

RCT

35
Q

Can study multiple outcome for one exposure. Can look at DIRECTION of cause of effect.

A

Cohort

36
Q

Good for studying rare dx. Can examine multiple exposures. Cost effective.

A

Case-Control

37
Q

Best for getting prevalence of disease or risk factor. Cheap and simple.

A

Cross-sectional survey

= relationship btwn dx (and other traits) as exist in defined pop’n at ONE point in time.

38
Q

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 (-)
A

Without condition who test negative.

**alway think it’s opposite of (+) predictive value.

39
Q

On the true positive and true negative table- what row and column is what?

A

True positive= PPV row; Sensitivity Column

True negative= (-) PV row; Specificity Column

40
Q

100 patients screened for colon CA. 30 (+) screen. 5 found to have colon cancer. What is positive predictive value:

A

True positive/
True positive + false positive

= 5/30

= 16.6%

41
Q

If newborn screen TOO sensitive - unacceptable # of:

  • false (-)
  • false (+)
  • inconclusive test
  • true (+)
  • true (-)
A

False (+) test

42
Q

T or F: (+) screen is dx for condition

A

False.

Require dx testing.

RC: Specialties Woo Hoo (31 decks)

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