EBM Flashcards
What is critical appraisal/evaluation?
the process of carefully and systematically examining research to judge its validity, results and clinical relevance
What do you evaluate in critical appraisal?
validity
results
clinical relevance
What does validity mean?
-how close to the truth (trustworthy) the study is
-OR how well it measures what it’s supposed to measure
(if potential sources of bias have been minimised, it improves the validity of the study)
What are the two parts of validity in critical appraisal?
- the internal validity: integrity of the experimental design (threated by biases)
- the external validity: appropriateness by which results can be applied to non-study patients or population
What question should we be asking with results?
What does the study show?
What are the results?
Are the results statically significant, and what is the size of the effect?
What does clinical relevance mean?
what the results means for a particular patient or context in which a decision is being made (= will the results help you and your patient?)
What is on the Critical Appraisal Checklist?
- Was the study original?
- Who was the study about?
- Was the study design sensible?
- Was bias avoided or minimised?
- Was assessment blind?
- Were preliminary statistical questions addressed?
What is in the hierarchy of evidence?
systematic reviews and meta-analysis randomised controlled trials cohort studies case-control studies cross-sectional surveys ecological studies case series and case reports ideas, editorials and opinions
What does the hierarchy of evidence do?
Gives an indication of the quality of evidence, reflecting reliability and validity
What are other systems for ranking the quality of evidence?
- GRADE (grading of recommendations assessment, development and evaluation)
- SIGN (scottish intercollegiate guidelines network
What is bias?
anything that influences the results of a study (or their interpretation) other than the experimental intervention
What are the different types of bias? (time wise)
pre-trila
during the trial
post trial
what are some potential sources of bias in pre-trial?
- selection bias: bias of selection or assignment of patients for a study that arises from study design rather than by chance, which occurs:
- subject studied are not representative of target population
- study of control groups are chosen so that they differ from each other by one or more farces that may affect the outcome of the study - definition bias
- bias of concepts
- bias due to concurrent disease
How can you minimise selection bias?
by random determination of who will be included in the study + including large sample of participants
what are some potential sources of bias during the trial?
1. information bias: errors in measuring exposure/intervention or outcome: leads to a systematic difference between groups participants in the study in terms of the information that is recorded (e.g. interviewers bias, recall bias, response bias) 2instruction bias 3. lead-time bias 4. attrition bias 4 Hawthorne effect
How can you minimise information bias?
with binding (where observers/assessors do not know which groups participants are in), by using objective assessment measures ans standardising assessment procedures
what are some potential sources of bias in post-trial?
- confounding: when outcome of the study is influenced by factors that are associated with the intervention/exposure(e.g. alcohol related to smoking, age related to amount of exercise)
- statistical bias: when the analysis of the results of the study is conducted in such a way as to lead to misleading conclusions (e.g. due to low statistical power or inappropriate statistical tests))
when is the basic flow chart of statistical tests used?
determine the most appropriate main dorm of statistical analysis to use in different circumstances
(chart is fairly basic/simplified)
What are continuous variables?
(a type of numerical variable) are me on a continuous scale: they can take any valu in a certain range
What are binary variables?
(a type of non-numerical or ‘categorical’ variable) are measured as one of two possible outcomes
What is a dependent variable?
outcome that you can measure and that is affected by other factors in the study (also referred to outcome variable)
What is an independent variable?
a factor thats being investigated to see if it has an effect on the dependent variable (so it is a potential ‘cause’ of the outcome) e.g. the use or non use of a particular drug (intervention via placebo –> binary independent variable)( also referred to ‘manipulated’ or ‘controlled’ variable)
draw out flow chart of statistical tests
(look at one note for answers)
Name two continuous dependent variable statistical with comparable groups.
- T test for difference between the means of 2 groups
- ANOVA (analysis of variance) for more than two treatment groups
Give an example of when ANOVA would be used?
to test the difference in 2 minute walk test outcome between stroke patients with
- no treatment
- low-intensty physiotherapy (1x per week)
- high-intensity physiotherapy (3x per week)
Give an example of when unpaired t-test would be used?
to test difference in 2 minute walk test outcome between stroke patients with and without physiotherapy
when do you use a categorical (e.g. binary) dependent variable and comparable groups?
Chi-square test
Why do you use the chi-square (xsquare) test?
to determine if observed frequency counts differ from expected frequency counts (to determine association between outcome and groups)
What is CAM (complementary and alternative medicine)?
therapies/interventions that are:
- non-standard/unconventional-non prescription
- non-surgical
- (can be pharmacological or non pharmacological)
What is the difference between complementary and alternative?
- complementary: as well as conventional treatment
- alternative: instead of conventional treatment
What is placebo?
any therapy which has no specific activity for the condition being treated (no active ingredient, no direct physiological effect
What is the placebo effect?
any favourable psychological or psychophysiological effect produced by placebos
what is the nocebo effect?
adverse psychological or psychophysiological effects produced by placebos
How does placebo work?
- expectancies (outcome expectancies and patient-related self-efficiency(feeling of control))
- conditioning
- anxiety reduction, social support
- psychophysiological mechanism
what are potential harmful effects of CAM?
- expensive
- unregulated
- can be harmful
- may be used as an alternative
when do you use linear regression?
- if you’re dependent (outcome) and independent variables are continuous
- if your dependent variable is continuous and you’re independent variable is not continuous but the groups are not alike (because no randomised control groups)
can you give a example of linear regression?
distant walked in two minutes and how many steps walked (or having different groups compared but are not randomised into groups i.e. low moderate and high exercise)
what does linear regression allow us to do?
- when 2 variables relate to each there, regression allows us to predict the dependent variable if we know the independent variable
- estimate the effects of confounding variables on the outcome
what is logical regression
same thing as linear regression but but is used when outcome variable is not continuous (i.e. binary outcome)
