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EBCP > EBCP > Flashcards

EBCP Flashcards

1
Q

What is selection bias?

A

Systematic differences in comparison groups, arising from the selection of participants.

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2
Q

What type of bias this this?

Systematic differences in comparison groups, arising from the selection of participants.

A

Selection Bias

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3
Q

What is considered a more severe form of selection bias?

A

Ascertainment Bias

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4
Q

What is another name for ascertainment bias?

A

Information bias

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5
Q

What type of bias is this?

Subjects belonging to a particular social group have medical records but others have to depend on recall.

A

Ascertainment / information bias

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6
Q

What is length bias?

A

A systematic error due to the inappropriate selection of long-duration cases.

Prevalence is dominated by those who survive for a longer duration. And these patients are qualitatively different from those who die early. Thus the sample may include disproportionately more of those who are healthier and survive longer. The conclusions can not be generalised to those who have less survival time.

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7
Q

What type of bias occurs when you are only measuring cases who survive longer, and you miss out on measuring cases who don’t survive as long (and therefore might posess different characteristics)?

A

Length bias

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8
Q

Which type of non-RCT measures the exposure first?

A

Cohort Study

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9
Q

What type of study measures the outcome first?

A

case-control study

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10
Q

Which type of study is not conducive to calculating incidence, prevelance, risk & risk ratio, and why?

A

Case Control Study

Because the incidence is set by the authors

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11
Q

What is Berkson Bias?

A

A specific form of selection bias when a case control study is performed in a hospital. Bias occurs if the exposure increases one’s chance of admission.

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12
Q

What type of bias occurs if you are performing a case control study in a hospital, and the exposure which you are measuring increases the chance of admission?

A

Berkson Bias

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13
Q

What type of bias can be reduce by blinding the assessors?

A

Detection bias / observer bias

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14
Q

What sort of bias can be reduced by blinding those who select participants?

A

Selection bias

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15
Q

What is observer bias?

A

Occurs when the observer unwittingly (or even intentionally) exercises more care about one type of responses or measurements such as those supporting a particular hypothesis than those opposing this hypothesis.

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16
Q

What type of bias occurs when the observer exercises more care about one type of responses or measurements such as those supporting a particular hypothesis than those opposing this hypothesis?

A

Observer Bias

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17
Q

What type of bias is recall bias?

A

Systematic error due to differences in the accuracy or completeness of recall to memory of past events or experiences.

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18
Q

What type of bias is a systematic error due to differences in the accuracy or completeness of recall to memory of past events or experiences?

A

Recall bias

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19
Q

What type of bias is the systematic error due to differences in characteristics between those who choose to participate in a study and those who do not.

A

Response Bias

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20
Q

What is response bias?

A

Systematic error due to differences in characteristics between those who choose to participate in a study and those who do not.

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21
Q

What type of bias describes the situation when a new or experimental test merely identifies the disease earlier than the previous and thus gives the impression that survival is prolonged?

A

Lead time bias

22
Q

What sort of bias does “Intention To Treat’ reduce?

A

Attrition Bias

23
Q

What is attrition bias?

A

Systematic differences between groups in withdrawals from a study. Withdrawals from the study lead to incomplete outcome data.

24
Q

How can you reduce attrition bias?

A

Intention to treat

25
Q

Describe what ITT analysis is

A

Analysing participants in the groups to which they were randomised, regardless of their compliance.

26
Q

Describe what per protocol analysis is

A

Analysing only those participants who were compliant with the treatment / placebo in the group to which they were assigned

27
Q

What is discrete data and give an example?

A

A type of ordinal data

Whole numbers

eg. number of children (1,2,3,4,>4)

28
Q

What is numerical data?

A

Data consisting of numberical scores

Includes variable and discrete data

29
Q

What is variable data?

A

A type of numerical data

Numbers which involve fractions and can be ranked

Eg. length (1cm, 1.25cm, 1.78cm)

30
Q

What is categorical data?

A

Non-numerical data

31
Q

What are the types of categorical data?

A

Ordinal & Nominal

32
Q

What is nominal data?

What is an example?

A

Nominal data is a type of categorical data

It is non-numerical data which can’t be ordered

Blood groups is an example

33
Q

What is ordinal data?

Give an example.

A

Ordinal data is categorical data which can be ordered

An example is Non-Smoker / Occasional Smoker / Frequent Smoker

34
Q

how do you calculate the relative risk reduction?

A

1 - relative risk

35
Q

how do you calculate the NNT?

A

1 - absolute risk reduction

36
Q

How do you test for publication bias in a systematic review?

A
37
Q

What is publication bias?

A

Publication bias is a systematic over or underestimate of effect due to selective publication of studies in a systematic review.

38
Q

what is used to calculate results in studies which used continuous (not dichotomous) outcomes?

A

Weighted mean difference (used when outcomes are measured on the same scale eg. BP)

Standardised mean difference (when outcomes are measured on different scales eg. pain / depression)

39
Q

What are the types of screenin?

A

Opportunistic Screening

Selective Screening

Mass Screening

40
Q

What is over-diagnosis?

A

A term usually used in the context of breast cancer.

Does NOT mean false +ve

But rather it refers conditions diagnosed by screening that would not otherwise have been diagnosed during a patient’s lifetime.

41
Q

What is interval cancer?

A

Usually used in the context of breast cancer

Cancers diagnosed in the interval between scheduled screening episodes in patients screened and given a ‘normal’ screening.

42
Q

What types of bias are associated with screening tests?

A

Lead time bias

Screening bias

43
Q

What is screening bias?

A

A form of selection bias.

Participants in screening programs tend to be healthier than those who don’t volunteer or comply.

44
Q

Which portoin of the ROC curve should be used to formulate the best “cut off pomt” for a positive / negative result for a test?

A

The top left corner

45
Q

What is on the x axis of a ROC curve?

What is on the y axis?

A

x axis = false +ve rate (1 - specificity)

y axis = true +ve rate (sensitivity)

46
Q

What is attributable risk?

A

The same as Absolute Risk Reduction

Risk (Exposed) - Risk (unexposed)

47
Q

what shape of funnel plot is more likely to show biased results?

A

Asymmetrical

“The more pronounced the asymmetry, the more likely it is that the amount of bias will be substantial.”

48
Q

What is statistical heterogenicity?

A

Identifies whether individual studies within a meta-analysis are similar enough to validate a meaningful interpretation from the meta-analysis

49
Q

How do you measure statistical heterogenicity?

A

Chi squared test

50
Q

How can you tell if a meta-analysis is statistically heterogenic?

A

chi-square statistic is larger than the degrees of freedom then there is evidence of heterogeneity

51
Q
A

EBCP (1 decks)

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