CRITICAL APPRAISAL AND STUDIES

Question 1

what are advantages of systematic reviews?

Answer 1

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

Question 2

what makes a search strategy on a data base strong?

Answer 2

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unpublished studies also included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

Question 3

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

Answer 3

studies with

weaker designs will be less valid and can overestimate effects.

Question 4

why are RCTs less prone to bias?

Answer 4

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

Question 5

what is a meta analysis?

Answer 5

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

Question 6

what is a 95% confidence interval?

Answer 6

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

Question 7

what is an odds ratio?

Answer 7

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

Question 8

why is random allocation important?

Answer 8

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

Question 9

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

Answer 9

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.

Question 10

what will make baseline characteristics similar?

Answer 10

if randomisation process worked and the trial is big enough

Question 11

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

Answer 11

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

Question 12

what should loss to follow up be?

Answer 12

<20%

Question 13

what does loss to follow up mean?

Answer 13

not

providing follow-up data at a particular time point.

Question 14

why is it important to use intention to treat analysis?

Answer 14

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

Question 15

why is blinding important?

Answer 15

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

Question 16

in what situation is blinding unimportant?

Answer 16

if the outcome is objective e.g death

Question 17

what is relative risk?

Answer 17

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

Question 18

how do you calculate relative risk?

Answer 18

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

Question 19

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

Answer 19

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.

Question 20

what is the absolute risk reduction/risk difference?

Answer 20

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

Question 21

how id absolute risk difference calculated?

Answer 21

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

Question 22

what is the relative risk reduction?

Answer 22

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

Question 23

how do we calculate relative risk reduction?

Answer 23

absolute risk reduction / risk of outcomes in control group

Question 24

what is number needed to treat?

Answer 24

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

Question 25

how do we calculate number needed to treat?

Answer 25

1/ absolute risk reduction

Question 26

what is a point estimate?

Answer 26

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

Question 27

what are some appropriate techniques to reduce confounding?

Answer 27

restriction, stratification, matching and multiple regression techniques

Question 28

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

Answer 28

risks missing a real association

Question 29

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

Answer 29

wastes money and is arguably unethical

Question 30

how do you calculate an odds ratio>

Answer 30

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

Question 31

what is an odds ratio?

Answer 31

a measure of association between an exposure and an outcome.

Question 32

how can you tell if evidence is precise?

Answer 32

small CI because of a large cohort

Question 33

how do you know if a CI is statistically significant?

Answer 33

it doesnt include 1.0

Question 34

what is a type 1 error?

Answer 34

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

Question 35

what is a type 2 eror?

Answer 35

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

Question 36

whats the difference between a random and systematic error?

Answer 36

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.

Question 37

what is selection bias?

Answer 37

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

Question 38

what is information bias?

Answer 38

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

Question 39

whats an observational study?

Answer 39

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.

Question 40

what is risk?

Answer 40

the probability that an event will occur during a specific time

Question 41

what is odds?

Answer 41

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

Question 42

which studies use odds ratios?

Answer 42

case-control mostly | cohort and cross-sectional can too

Question 43

which study uses relative risk?

Answer 43

cohort studies

Question 44

what is prevalence and how do you calculate it?

Answer 44

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

Question 45

what is incidence and how do you calculate it?

Answer 45

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

Question 46

what are some problems with historical studies?

Answer 46

has the standard care changed? | are the groups of people you are comparing similar?

Question 47

whats the main problem with before and after studies

Answer 47

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

Question 48

why do we randomise?

Answer 48

to eliminate systematic bias in allocation of interventions | to ensure balance across comparative groups for any confounding variables that could affect the outcome

Question 49

what are some ethical considerations given to RCTs?

Answer 49

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

Question 50

what is stratification? whats the purpose?

Answer 50

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

Question 51

what is ascertainment bias?

Answer 51

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

Question 52

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

Answer 52

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.

Question 53

what are some ways to randomise in an RCT?

Answer 53

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.

Question 54

whats the best method of allocation concealment?

Answer 54

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

Question 55

what does a vertical line on a forest plot represent? 2. what does it mean if the confidence intervals for individual studies overlap with this line? 3. what does it mean if the meta analysed measure of effect (big diamond) overlaps this line?

Answer 55

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.

Question 56

what does a forest plot do?

Answer 56

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.

Question 57

why are forest plots useful?

Answer 57

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

Question 58

what are the 3 discrete steps in critical appraisal?

Answer 58

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

Question 59

what is study validity?

Answer 59

the believability or credibility of the results

Question 60

whats the intention to treat analysis?

Answer 60

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.

Question 61

what is an RCT?

Answer 61

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

Question 62

what is randomisation?

Answer 62

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

Question 63

what is relative risk?

Answer 63

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

Question 64

what is the relative treatment effect?

Answer 64

The effect of a treatment relative to another treatment or control

Question 65

what is reliability?

Answer 65

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

Question 66

what is a cohort study?

Answer 66

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.

Question 67

what are the advantages of cohort studies?

Answer 67

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

Question 68

what are disadvantages of cohort studies?

Answer 68

expneisve time consuming confounding factors problems with loss to follow up

Question 69

what is a case control study?

Answer 69

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!

Question 70

what are the advantages of case-control studies?

Answer 70

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

Question 71

what are the disadvantages of case-control studies?

Answer 71

recall bias

Question 72

what should systematic reviews have in their inclusion criteria?

Answer 72

papers that have not been published | papers not in English

Question 73

what are the benefits of systematic reviews?

Answer 73

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

Question 74

what study should be used for an aetiology question type?

Answer 74

cohort study -> case control

Question 75

what study should be used for a prognosis question?

Answer 75

cohort study -> case control

Question 76

what study should be used for a diagnosis question?

Answer 76

cross-sectional

Question 77

what study should be used for a treatment question?

Answer 77

RCT -> cohort -> case control

Question 78

what is confounding?

Answer 78

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

Question 79

how can you reduce confounding?

Answer 79

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

Question 80

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

Answer 80

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

Question 81

which studies often have confounding?

Answer 81

observational

Question 82

what is the subjective expected utility?

Answer 82

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

Question 83

what are normative decisions?

Answer 83

the most ideal decision for a given situation

Question 84

what is evidence?

Answer 84

any factor that can and should influence clinical decision making

Question 85

what is a critical appraisal?

Answer 85

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

Question 86

what are some pros of cortical appraisal in practice?

Answer 86

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

Question 87

what are some cons of using critical appraisals in practice?

Answer 87

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

Question 88

what is blinding?

Answer 88

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.

Question 89

what is power?

Answer 89

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

Question 90

what are confidence intervals?

Answer 90

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

Question 91

whats the difference between risk and odds?

Answer 91

“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.

Question 92

what is absolute risk?

Answer 92

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

Question 93

what are baseline characteristics?

Answer 93

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.

Question 94

what is a meta analysis?

Answer 94

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

Question 95

what is validity?

Answer 95

the extent to which something measures what it claims to measure

Question 96

what is reliability?

Answer 96

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

Question 97

what is the difference between internal and external validity?

Answer 97

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

Question 98

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

Answer 98

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

Question 99

how can you calculate the power of a study?

Answer 99

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

Question 100

how can the power of a study be increased?

Answer 100

increasing the sample size

Question 101

what are the properties of normal distribution?

Answer 101

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

Question 102

what is standard deviation?

Answer 102

a measure of how much dispersion exists from the mean

Question 103

what is the null hypothesis?

Answer 103

states that two treatments are equally effective

Question 104

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

Answer 104

the results of the study generalise well to other populations

Question 105

what is the power of a study?

Answer 105

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

Question 106

what is validity?

Answer 106

the extent to which something measures what it claims to measure

Question 107

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?

Answer 107

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.

Question 108

what is selection bias?

Answer 108

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

Question 109

what is recall bias?

Answer 109

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

Question 110

what is publication bias?

Answer 110

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

Question 111

what is expectation bias?

Answer 111

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

Question 112

what is procedure bias?

Answer 112

Occurs when subjects in different groups receive different treatment

Question 113

what is lead time bias?

Answer 113

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

Question 114

what is lead time?

Answer 114

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

Question 115

what is length time bias?

Answer 115

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

Question 116

What is an adjusteD odds ratio?

Answer 116

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.

Question 117

What would an adjusted odds ratio of 1.04 mean?

Answer 117

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

Question 118

What is stratification for?

Answer 118

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]

Question 119

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

Answer 119

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

Question 120

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

Answer 120

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