Evidence based paediatrics Flashcards
Describe a crossover study and what is more ‘powerful’ than it.
Variation of RCT. All patients recieve treatments, but order is randomised and blinded.
RCT
Describe a RCT and what is more powerful than it
Subjects are randomly assigned to one of two groups (experimental versus control) with the only expected difference being the outcome studied
Describe a case-control study and what is more powerful than it.
Retrospective. Not conducted over time.
Researchers choose individuals with a particular characteristic (the cases) and compare features of interest with a control group of individuals who do not have the characteristic. This type of study is required for questions around causation.
Cohort, RCTs ,Crossover
Describe a cohort study and what is more powerful than it
follow individuals with a particular condition or who receive a particular treatment and they are compared with another group of people who are not affected by the condition or who did not receive the treatment.
Crossover, RCTs
Describe a cross-sectional study and what is more powerful than it
defined population is observed at a single point in time or at certain time intervals
case-control, Cohort, crossover RCTs
Define Selection bias
is linked to the recruitment of patients; a cohort of individuals deciding not to participate in the study could lead to under- or overestimation of a particular effect or risk. Patients lost to follow-up, self-selection into a study and lack of randomisation are further examples.
Define information bias
Occurs when patients are misclassified, for example, when individuals with a particular disease or exposure are classified as nondiseased or nonexposed due to an inaccuracy of diagnostic tests. Such a problem will invalidate outcomes.
Define confounding variable
are variables that influence both the dependent variable and independent variable, causing a spurious association. Confounding variables are those that may compete with the exposure of interest (e.g. treatment)
in explaining the outcome of a study. For example, in a study about whether a lack of exercise (independent variable) leads to weight gain (dependent variable) in children, the number of calories consumed would be a confounding variable. Identifying possible confounders early on and controlling for them will assist in eliminating bias.
Define number needed to treat
number of patients that need to be treated in order for one to benefit. For example, an NNT of 20 would be interpreted as ‘20 patients need to be treated to avoid one additional death’.
Give an example of when a Chi squared test would be used
Chi-squared tests are commonly performed on 2 x 2 data, for example, to investigate if there is an association between maternal smoking (yes or no) and child’s asthma status (asthmatic or not asthmatic) in a given population
What is the null hypothesis?
That we accept that there is no significant differeence between results. IF P value is <0.05, then we say it is significant and thus we REJECT the null hypothesis.
What does a 95% confidence interval (95% CI) mean?
there is a 5% chance that the ‘true’ population mean lies outside the quoted range.
How do you determine if there is significant result in confidence intervals following a given intervention?
95% CI do not overlap
e.g daily steps undertaken by the teenagers increased from 12.3k (95% confidence intervals (CI) 7.5 to 14.1) to 17.7k (95% CI 15.2 to 20.3) after the exercise programme
When interpreting confidence intervals between means, the confidence interval crossing 0 means what?
the studied effect is not significant as zero indicates no difference between means
When interpreting confidence intervals between means, the confidence interval being entierly negative or positive numbers means what?
the studied effect is significant as the 95% confidence interval does not cross zero
When Interpreting a 95% CI for ratios (OR, RR etc), what does it mean if the CI crosses 1?
There is no difference between arms of the study and the outcome of the study can be interpreted as not statistically significant
When Interpreting a 95% CI for ratios (OR, RR etc), what does it mean if the CI is <1 but does not cross it?
the intervention is likely to be less effective and, as the ratio does not cross 1, the findings are statistically significant
When Interpreting a 95% CI for ratios (OR, RR etc), what does it mean if the CI is >1 and does not cross it?
the intervention is likely to be more effective and, as the ratio does not cross 1, the findings are statistically significant
What does an odds ratio do?
Determine whether a particular exposure is a risk factor for a particular outcome and to compare the magnitude of various risk factors for that outcome.
What does OR = 1 mean?
Observed outcome is the same in the two groups
What does OR = <1 mean?
Intervention provides a poorer outcome
What does OR = >1 mean?
Intervention provides a better outcome
Describe relative risk
the probability that an event will occur, whether it be a desirable or undesirable event. It explains how many times more likely that an event will occur in the treatment/intervention/exposure group, relative to the control group.
What does RR = 1 mean?
No difference in given event occuring between two groups
What does RR <1 mean?
Given even less likely to occur with exposure
What does RR > 1 mean?
Given event more likely to occur with exposure
Define risk difference (RD)
The difference in risk of a condition, such as a disease, between an exposed group and an unexposed group.
If RR1 is the disease risk in an exposed population and RR2 is the disease risk in a nonexposed population then the risk difference (RD) equals RR1–RR2. RD can therefore be a number between -1 and +1.
What does RD = >0 mean?
Increased risk in exposed group
What does RD = 0 mean?
No difference in risk between groups
What does RD =<0 mean?
Decreased risk in exposed group
Define Specificity
Probability test is negative when disease is absent
Define Sensitivity
Probability test is positiive when disease is present
Define positive predicitive value
Probability Test is postitive when disease is absent
Define negative predicitive value
Probability test is negative when disease is absent
