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YEAR 2 H&S > CRITICAL APPRAISAL AND STUDIES > Flashcards

CRITICAL APPRAISAL AND STUDIES Flashcards

1
Q

what are advantages of systematic reviews?

A

its a rigorous summary of all the research evidence that relates to a specific question
by bringing together all the relevant evidence, disadvantages of single studies can be gaurded against e.g. larger sample size, less false negative results and increases power
able to see if effects are consistent across different clinical populations
identifies all available evidence rather than cherry picking evidence

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2
Q

what makes a search strategy on a data base strong?

A

look at multiple data bases
look at publications in all languages
use grey literature
unpublished studies also included
no date or publication type restrictions applied
manual searches were done too by contacting the author

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3
Q

why is it important to assess the quality of a study in a systematic review?

A

studies with

weaker designs will be less valid and can overestimate effects.

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4
Q

why are RCTs less prone to bias?

A

groups are likely to be similar with respect tp known and unknown determinants of outcome so we can be confident that any observed differences in outcome are due to the intervention
randomisation of allocation of groups which means any observed differences in outcome are due t the intervention not baseline characteristic differences

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5
Q

what is a meta analysis?

A

a statistical technique for combining the results of multiple studies that measure the same outcome into a single summative estimate

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6
Q

what is a 95% confidence interval?

A

the range between two value within with it is 95% probable that the true value lies for the whole population of patients from which the study patients are selected

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7
Q

what is an odds ratio?

A

a ratio of the odds of an event in an exposed group to the odds of the same event in a group not exposed

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8
Q

why is random allocation important?

A

to eliminate selection bias and balance known and unknown confounding factors in order to create a control group that is as similar as possible to the treatment group

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9
Q

why is it important that baseline characteristics are similar at the start of the study?

A

If the groups are different at the start of the study (i.e. baseline), then it will be unclear whether
any effect of the intervention was because of this original difference or because the actual
intervention had an effect.

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10
Q

what will make baseline characteristics similar?

A

if randomisation process worked and the trial is big enough

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11
Q

why is it important that groups are treated the same, other than the intervention?

A

If the groups were treated differently (e.g. one group had more consultations with a doctor, or
more tests) then it could be that it was the different treatment one group received that has
caused a differences in outcome, rather than the intervention itself. The strength of the RCT
design is the element of control (hence the name); that is, changing something about a patient’s
treatment while controlling other things

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12
Q

what should loss to follow up be?

A

<20%

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13
Q

what does loss to follow up mean?

A

not

providing follow-up data at a particular time point.

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14
Q

why is it important to use intention to treat analysis?

A

to preserve the value of randomisation
If the trial loses a lot of patients during the intervention, it reduces the sample size and weakens
the findings. If patients are lost from one group more than another in a trial, this can bias the
results

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15
Q

why is blinding important?

A

This is necessary to avoid the patient’s reporting of symptoms or the clinician’s interpretation of
them being affected by whether they know which group the patients is in, and whether or not
they think the treatment is effective

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16
Q

in what situation is blinding unimportant?

A

if the outcome is objective e.g death

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17
Q

what is relative risk?

A

how many times more likely it is that an event will occur in the treatment group relative to the control group.

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18
Q

how do you calculate relative risk?

A

risk of outcome in treatment group / risk of outcome in control group

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19
Q

what does a relative risk of <1 mean? what does a relative risk of >1 mean?

A

An RR <1 means that the treatment decreases the risk of an outcome. An RR >1 means that the treatment increased the risk of an outcome.

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20
Q

what is the absolute risk reduction/risk difference?

A

the difference between the risk of an outcome in the exposed group and the unexposed group.

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21
Q

how id absolute risk difference calculated?

A

risk of the outcome in control group - risk of outcome in treatment group

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22
Q

what is the relative risk reduction?

A

It tells us the reduction of the rate of the outcome in the treatment group relative to that in the control group.

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23
Q

how do we calculate relative risk reduction?

A

absolute risk reduction / risk of outcomes in control group

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24
Q

what is number needed to treat?

A

s the number of patients we need to treat with the experimental therapy (rather than the control group therapy) in order to prevent one bad outcome over a stated period of time

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25
Q

how do we calculate number needed to treat?

A

1/ absolute risk reduction

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26
Q

what is a point estimate?

A

the use of sample data to calculate a single value which is to serve as a “best guess” or “best estimate” of an unknown population parameter

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27
Q

what are some appropriate techniques to reduce confounding?

A

restriction, stratification, matching and multiple regression techniques

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28
Q

whats the issue with having a follow-up period that is too short?

A

risks missing a real association

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29
Q

whats the issue with having a follow-up period that is too long?

A

wastes money and is arguably unethical

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30
Q

how do you calculate an odds ratio>

A

dividing the odds of the first group by the odds in the second group

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31
Q

what is an odds ratio?

A

a measure of association between an exposure and an outcome.

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32
Q

how can you tell if evidence is precise?

A

small CI because of a large cohort

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33
Q

how do you know if a CI is statistically significant?

A

it doesnt include 1.0

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34
Q

what is a type 1 error?

A

when you mistakenly reject the null hypothesis when it is actually true (false positive)

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35
Q

what is a type 2 eror?

A

mistakenly accept the null hypothesis when the alternative hypothesis is actually true (false negative)

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36
Q

whats the difference between a random and systematic error?

A

Random error mainly affects precision, which is how reproducible the same measurement is under equivalent circumstances. In contrast, systematic error affects the accuracy of a measurement, or how close the observed value is to the true value.

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37
Q

what is selection bias?

A

systematic error in creating intervention groups, such that they differ with respect to prognosis due to baseline characteristics and are not representative of the population

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38
Q

what is information bias?

A

the bias that occurs during data collection and causes a systematic error

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39
Q

whats an observational study?

A

where researchers observe the effect of a risk factor, diagnostic test, treatment or other intervention without trying to change who is or isn’t exposed to it.

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40
Q

what is risk?

A

the probability that an event will occur during a specific time

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41
Q

what is odds?

A

the probability that an event will or will not happen (likelihood or a particular outcome)

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42
Q

which studies use odds ratios?

A

case-control mostly

cohort and cross-sectional can too

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43
Q

which study uses relative risk?

A

cohort studies

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44
Q

what is prevalence and how do you calculate it?

A

proportion of persons who have a condition at or during a particular time period
number of individuals having the disease at a specific time/number of individuals in the population at the point in time

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45
Q

what is incidence and how do you calculate it?

A

proportion of persons who have a condition at or during a particular time period
sum of all new episodes of disease / total population in a specific time period

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46
Q

what are some problems with historical studies?

A

has the standard care changed?

are the groups of people you are comparing similar?

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47
Q

whats the main problem with before and after studies

A

regresson to the mean - the tendency of results that are extreme by chance on first measurement to move closer to the average when measured a second time

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48
Q

why do we randomise?

A

to eliminate systematic bias in allocation of interventions

to ensure balance across comparative groups for any confounding variables that could affect the outcome

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49
Q

what are some ethical considerations given to RCTs?

A

treatment is not decided by the person and we do not know which intervention is better

50
Q

what is stratification? whats the purpose?

A

the arrangement or classification of something into different groups
prevents imbalance between treatment groups for known factors that influence prognosis or treatment responsiveness - often used when randomisation cant balance baseline factors alone

51
Q

what is ascertainment bias?

A

systematic distortion of the results of a randomised trial as a result of knowledge of the group assignment by the person assessing the outcome

52
Q

how would bias affect results depending on if the healthiest or sickest patients were chosen for the intervention?

A

If there is bias in allocation due to the healthiest patients being chosen, the effect of the intervention would be exaggerated. If the bias is the other way, i.e. the sickest patients need the intervention, then the effects of the intervention would be diluted.

53
Q

what are some ways to randomise in an RCT?

A

simple - Randomization based on a single sequence of random assignments e.g. flipping a coin
block - randomizing participants within blocks such that an equal number are assigned to each treatment
stratified - a two-stage procedure in which patients who enter a clinical trial are first grouped into strata according to clinical features that may influence outcome risk. Within each stratum, patients are then assigned to a treatment according to separate randomization schedules
covariate adaptive - first stratify according to baseline covariates and then assign treatment status so as to achieve “balance” within each stratum.

54
Q

whats the best method of allocation concealment?

A

using an independent organisation to centrally organise randomised allocation via a computer programme

55
Q

what does a vertical line on a forest plot represent?

  1. what does it mean if the confidence intervals for individual studies overlap with this line?
  2. what does it mean if the meta analysed measure of effect (big diamond) overlaps this line?
A
  1. no effect
  2. It demonstrates that at the given level of confidence their effect sizes do not differ from no effect for the individual study - any study line which crosses the line of null effect does not illustrate a statistically significant result
  3. if the points of the diamond overlap the line of no effect the overall meta-analysed result cannot be said to differ from no effect at the given level of confidence.
56
Q

what does a forest plot do?

A

is take all the relevant studies asking the same question, identifies a common statistic in said papers and displays them on a single set of axis.

57
Q

why are forest plots useful?

A

allows you to compare directly what the studies show and the quality of that result all in one place.

58
Q

what are the 3 discrete steps in critical appraisal?

A

are the results of the study valid
what are the results
can I apply the results to this patients care

59
Q

what is study validity?

A

the believability or credibility of the results

60
Q

whats the intention to treat analysis?

A

all participants who are randomized are included in the statistical analysis and analyzed according to the group they were originally assigned, regardless of what treatment (if any) they received.

61
Q

what is an RCT?

A

A study in which a number of similar people are randomly assigned to 2+ groups to test a specific drug, treatment or other intervention. One group has the intervention being tested, the other has an alternative intervention, placebo or no intervention at all. The groups are followed up to see how effective the experimental intervention was. Outcomes are measured at specific times and any difference in response between the groups is assessed statistically

62
Q

what is randomisation?

A

Assigning people in a research study to different groups without taking any similarities or differences between them into account.

63
Q

what is relative risk?

A

The probability of an event occurring in the study group compared with the probability of the same event occurring in the control group, described as a ratio

64
Q

what is the relative treatment effect?

A

The effect of a treatment relative to another treatment or control

65
Q

what is reliability?

A

The ability to get the same or similar result each time a study is repeated with a different population or group.

66
Q

what is a cohort study?

A

An observational study with 2 or more groups of people with similar characteristics. One group has a treatment, is exposed to a risk factor or has a particular symptom and the other group does not. The study follows their progress over time and records what happens.

67
Q

what are the advantages of cohort studies?

A

good for rare risk factors
can assess multiple risk factors at once
prospective

68
Q

what are disadvantages of cohort studies?

A

expneisve
time consuming
confounding factors
problems with loss to follow up

69
Q

what is a case control study?

A

An observational study to find out the possible cause of a disease or condition. This is done by comparing a group of patients who have the disease with a group of people who do not have it but who are otherwise as similar as possible. This means the researcher can look for aspects of their lives that differ to see if they may have caused the condition.
retrospective!

70
Q

what are the advantages of case-control studies?

A

good for rare diseases
good for tracing source of an outbreak
can look at multiple risk factors

71
Q

what are the disadvantages of case-control studies?

A

recall bias

72
Q

what should systematic reviews have in their inclusion criteria?

A

papers that have not been published

papers not in English

73
Q

what are the benefits of systematic reviews?

A

include all the available evidence to answer a question
includes research that is unpublished or published in non-english
increases the total sample size which increases certainty and precision
indicates heterogeneity in findings
permits sub-group analyses
permist sensitivity analyses

74
Q

what study should be used for an aetiology question type?

A

cohort study -> case control

75
Q

what study should be used for a prognosis question?

A

cohort study -> case control

76
Q

what study should be used for a diagnosis question?

A

cross-sectional

77
Q

what study should be used for a treatment question?

A

RCT -> cohort -> case control

78
Q

what is confounding?

A

a variable that influences both the dependent variable and independent variable, causing a spurious association

79
Q

how can you reduce confounding?

A

restriction - Restriction eliminates variation in the confounder (for example if an investigator only selects subjects of the same age or same sex then, the study will eliminate confounding by sex or age group
matching - Create a comparison group matched on the possible confounder.
stratification

80
Q

whats the problem with restriction in an effort to reduce confounding?

A

it means you have less data and there may be confounding variables you have not thought about

81
Q

which studies often have confounding?

A

observational

82
Q

what is the subjective expected utility?

A

the attractiveness of an economic opportunity as perceived by a decision-maker in the presence of risk

83
Q

what are normative decisions?

A

the most ideal decision for a given situation

84
Q

what is evidence?

A

any factor that can and should influence clinical decision making

85
Q

what is a critical appraisal?

A

process of systematically examining research evidence to assess its validity, results and relevance before using it to inform a decision.

86
Q

what are some pros of cortical appraisal in practice?

A

its a systematic way of assessing validity, results and usefulness of published research paper
a route to closing the gap between research and practice
stops us from accepting the voice of authority
allows us to handle a great deal of evidence

87
Q

what are some cons of using critical appraisals in practice?

A

time consuming initially
doesnt always provide an easy answer
can be disappointing if it highlights a lack of good evidence

88
Q

what is blinding?

A

where study participants are prevented from knowing certain information that may somehow influence them
A way to prevent researchers, doctors and patients in a clinical trial from knowing which study group each patient is in so they cannot influence the results.

89
Q

what is power?

A

the likelihood that a researcher will find a significant result in a sample if such an effect exists in the population being studied

90
Q

what are confidence intervals?

A

a range of values so defined that there is a specified probability that the value of a parameter lies within it

91
Q

whats the difference between risk and odds?

A

“Risk” refers to the probability of occurrence of an event or outcome. Statistically, risk = chance of the outcome of interest/all possible outcomes. The term “odds” is often used instead of risk. “Odds” refers to the probability of occurrence of an event/probability of the event not occurring.

92
Q

what is absolute risk?

A

The likelihood of an event or outcome occurring (for example, an adverse reaction to the drug being tested) among the group being studied

93
Q

what are baseline characteristics?

A

demographic, medical and other information, particularly prognostic variables. Researchers collect this information about each participant at the beginning of a study, before they have received the treatments that are going to be compared in a treatment comparison.

94
Q

what is a meta analysis?

A

A statistical technique for quantitatively combining the results of multiple studies that measure the same outcome into a single pooled or summary estimate.

95
Q

what is validity?

A

the extent to which something measures what it claims to measure

96
Q

what is reliability?

A

the extent to which an experiment, test, or any measuring procedure yields the same result on repeated trials

97
Q

what is the difference between internal and external validity?

A

Internal validity refers to the degree of confidence that the causal relationship being tested is trustworthy and not influenced by other variables
External validity refers to the extent to which results from a study can be applied

98
Q

what is a type 1 error? how is it linked to P value?

A

null hypothesis is rejected when its true.

As the p value decreases the chance of a type 1 error decreases
as p value increases, chance of type 2 error decreases

99
Q

how can you calculate the power of a study?

A

Power - the probability of correctly rejecting the null hypothesis when it is false ( 1- probability of type 2 error).

100
Q

how can the power of a study be increased?

A

increasing the sample size

101
Q

what are the properties of normal distribution?

A

its symmetrical i.e. mean=mode=median
68.3% of values lie within 1SD of the mean, 95.4% of values lie within 2SD of the mean and 99.7% of value lie within 3SD of the mean

102
Q

what is standard deviation?

A

a measure of how much dispersion exists from the mean

103
Q

what is the null hypothesis?

A

states that two treatments are equally effective

104
Q

what does it mean when a study has good external validity?

A

the results of the study generalise well to other populations

105
Q

what is the power of a study?

A

the probability of correctly rejecting the null hypothesis when it is false

106
Q

what is validity?

A

the extent to which something measures what it claims to measure

107
Q

There were 60 participants taking the new medication of which 20 had an improved PHQ-9 score. In the placebo group, there were 100 participants with 20 of this group going on to have an improved PHQ-9 score.

What is the odds ratio for this study?

A

there were 20 participants with an improved PHQ-9 in the medication group and 40 who did not which is an odds of 0.5. In the placebo group, 20 participants had an improved score whereas 80 did not which is a odds of 0.25. The exposure odds are divided by the odds in the group without exposure so 0.5 is divided by 0.25 which is 2.

108
Q

what is selection bias?

A

Error in assigning individuals to groups leading to differences which may influence the outcome

109
Q

what is recall bias?

A

Difference in the accuracy of the recollections retrieved by study participants, possibly due to whether they have disorder or not.

110
Q

what is publication bias?

A

Failure to publish results from valid studies, often as they showed a negative or uninteresting result.

111
Q

what is expectation bias?

A

Observers may subconsciously measure or report data in a way that favours the expected study outcome
(only a problem in non blinded trials)

112
Q

what is procedure bias?

A

Occurs when subjects in different groups receive different treatment

113
Q

what is lead time bias?

A

when survival time appears longer because diagnosis was done earlier, irrespective of whether the patient lived longer.

114
Q

what is lead time?

A

duration of time between detection of a disease and its usual clinical presentation and diagnosis.

115
Q

what is length time bias?

A

screening tends to detect less aggressive diseases (because of slower onset) which have a better prognosis so this overestimates survival time

116
Q

What is an adjusteD odds ratio?

A

useful for telling us how changes in one predictor variable affect the odds of a response variable occurring, after controlling for other predictor variables in a model.

117
Q

What would an adjusted odds ratio of 1.04 mean?

A

That you are 4% more likely to have that outcome when all counfounding variables are accounted for

118
Q

What is stratification for?

A

Stratification can be used to ensure equal allocation of subgroups of participants to each experimental condition. This may be done by gender, age, or other demographic factors. Stratification can be used to control for confounding variables (variables other than those the researcher is studying), thereby making it easier for the research to detect and interpret relationships between variables.[1] For example, if doing a study of fitness where age or gender was expected to influence the outcomes, participants could be stratified into groups by the confounding variable. A limitation of this method is that it requires knowledge of what variables need to be controlled.[1]

119
Q

why is it beneficial to include non-english articles in a systematic review?

A

as statistically significant results are more likely to be translated into English than non-significant results but they are equally important when conducting a systematic review - language bias

120
Q

why is it good for two authors to discuss disparities within studies of a systematic review?

A

assessing quality is important because studies with weaker designs will be less valid and can overestimate effects
using 2 independent reviewers to assess quality makes it less likely errors will be made
using pre-agreed criteria helps to make the process objective and transparent

YEAR 2 H&S (6 decks)

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