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CAT Flashcards

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Sociology 101 flashcards
1
Q

What is heterogeneity?

A

Means variability in data - estimates how effective Tx different between studies

Clinical - differences in participants, interventions or outcomes
Methodological - differences in study design, risk of bias
Statistical - variation in intervention effects or results

Forest plot - overlapping CI’s

I^2 - 0% to 40%: might not be important
30% to 60%: moderate heterogeneity
50% to 90%: substantial heterogeneity
75% to 100%: considerable heterogeneity

Can’t do meta-analysis if heterogeneity is too high

Explore heterogeneity - done by subgroup analysis or meta-regression

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2
Q

Causes of publication bias?

A

Failure to publish/include results from valid studies, often because they show a negative or uninteresting result

Important in meta-analyses and SRs where studies showing negative results may be excluded

E.g., abstract not included

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3
Q

What is intention to treat analysis?

A

Analysis based on the initial treatment intended from allocation, not the treatment eventually given (e.g., if patient dropped out)

Keep individual in group, even if not treated

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4
Q

What is concealment of allocation?

A

The person randomising the patients does not know what the next treatment allocation will be, preventing selection bias

Prevent prediction

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5
Q

What is blinding?

A

Where some of the participants of trial (patient/clinicians/researchers) are prevented from knowing certain information that may lead to conscious or subconscious bias

Prevent conscious/unconscious bias

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6
Q

What is meta analysis?

A

Research process used to systemically synthesis or merge findings of single, independent studies, using stat. methods to calculate an overall or ‘absolute’ effect

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7
Q

Cohort studies are prone to…

A

Dropouts and non-completion > lack of follow > bias

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8
Q

Benefits of using medical records?

A

Objective information

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9
Q

Problems of rating scales

A

Tendency to overdiagnose mood disorders

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10
Q

How do studies try to tackle confounding

A

Excluding pt’s from sample

Measuring factors and adjusting

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11
Q

What is Zelens procedure

A

participants are randomly allocated and then approached and offered the group to which they were allocated

used firstly, to reduce disappointment bias in the conventional consent-randomization process, and secondly, to remove subjective bias in the recruitment process.

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12
Q

What is bias?

A

Systematic error in measurement

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13
Q

Methods of randomisation

A

Simple - allocated 1:1 or within each block of 6

Stratified - allocate randomly, often testing characteristics (i.e., severity of condition)

Minimisation - uses a computer algorithm to create balance in groups, according to characteristics

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14
Q

Why do SR?

A

single study may not provide definitive answer

combine single studies and may provide new evidence (may be unethical to do new primary research)

promotive a scientific (not subjective) approach to summarising information

reduce inaccuracies from bias and enhance replication

provide reliable and ‘speedier’ evidence

more statistical power

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15
Q

What is confounding?

A

variable that has relationship between both the exposure and outcome

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16
Q

How can confounding be addressed in design + analysis?

A

restriction (to entry of study)

matching (participants to study)

stratification (according to variable)

multiple variable regression (predict one variable from another)

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17
Q

What can go wrong in cohort study?

A

misclassification of exposure

differential follow-up between exposed/non-exposed

outcome assessment not blind to exposure category

failure to recognise and address possibility of confounding

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18
Q

What is treatment fidelity?

A

how accurately the intervention is reproduced from a protocol or model?

19
Q

What is internal validity?

A

accuracy - how well the study was conducted, taking confounders into account and removing bias

20
Q

What is external validity?

A

generalisability - how well the study can be applied to different scenarios

21
Q

What is selection bias?

A

Error in assigning individuals to groups leading to differences that may influence the outcome. The subjects are not representative of the population

Sampling bias - selected subjects are not representative of the population
Volunteer bias - the volunteer subjects are not representative of the population
Non-responder bias - the respondents are not representative of the population

Particular problem in cohort studies

22
Q

What is recall bias?

A

Difference in the accuracy of recollection of study participants, possibly due to whether they have the outcome or not

Problem in case-control studies

23
Q

What is publication bias?

A

Failure to publish/include results from valid studies, often because they show a negative or uninteresting result

Problem in meta-analyses and SRs

24
Q

What is work up bias?

A

Verification bias

Seen in studies trying to validate a new diagnostic test

Refers to the gold-standard test being performed more frequently in patients who already had a positive result from the new test

25
Q

What is expectation bias?

A

Pygmalion effect

Only a problem in non-blinded trials

Observers may subconsciously measure or report data in a way that favours the expected study outcome

26
Q

What is Hawthorne effect?

A

Group changing its behaviour due to the knowledge that it is being studied

27
Q

What is procedure bias?

A

Subjects in different groups receive different treatment, others than just the interventions

28
Q

What is length time bias

A

Screen over represents less-aggressive disease

e.g., aggressive tumours have a shorter asymptomatic period, so screening less likely to detect aggressive tumours, but more likely to detect slow-growing tumours with long asymptomatic periods. Slow growing tumour has greater survival, so appears screening improves survival

29
Q

What is lead time bias

A

Early diagnosis appears to prolong survival

30
Q

What is late-look bias

A

Gathering information at an inappropriate time

e.g., studying fatal disease many years alter when some patients may have died

31
Q

Advantages of cohort studies

A

Best information about causation of disease, can work out incidences

Able to examine a range of outcomes from a particular exposure

Good for rare exposures - can select those exposed to certain things

32
Q

Advantages of case control study

A

Simple/easy to conduct, do not require long follow up as outcome is already present

Good for rare outcomes - can select all patients with certain disease

Good for long latent periods - finding patients after disease developed, not waiting for it after exposure

33
Q

Disadvantages of case control study

A

Bad for rare exposures - would require enormous sample size

Controls may not represent the population where the sample is from

Cases don’t represent full disease spectrum

Recall bias - different reporting of exposure from different groups

Confounders - not recognised/addressed

34
Q

What is equipoise?

A

Where the researchers have no preference between the two interventions

35
Q

Underpowered trials lead to…

A

insufficient no of participants so real effect cannot be established from random variation

Causes T2 statistical error - accepting null hypothesis when it is false

36
Q

Why combine data in meta analysis

A

^ number of patients being analysed (increases sample size)

Improves precision and reduces the width of CIs

Can demonstrate a statistically significant result when none of the trials could do this individually

37
Q

Challenges to measuring exposure in case controls

A

Recall bias

Variable exposure - patients environment may have changed (e.g., moved house)

Unavailable data - pt. can’t remember, medical records unavailable, incomplete, inaccurate

38
Q

Limiting confounding in cohort study

A

Restriction - limit participants

Matching and stratification - make comparison groups (with and without confounder) - used for things like age and sex

Multiple variable regression - coefficients are established for the confounder groups, allows for better adjustment

39
Q

What is likelihood ratio for a positive test result

A

How much the odds of the disease increase when a test is positive

40
Q

What is likelihood ratio for a negative test result

A

How much the odds of the disease decrease when a test is negative

41
Q

What is PPV

A

The chance that the patient has the disease if the test is positive

42
Q

What is NPV

A

Chance the patient does not have the disease if the test is negative

43
Q

What is sensitivity

A

Proportion of patients with the disease who get a positive test result

44
Q

What is specificity

A

Proportion of patients without the disease who get a negative test result

Health and Society (4 decks)

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