Critical appraisal Flashcards
What is meany by the Number Needed to Treat (NNT)
The NNT measures the number of patients who need to receive a treatment to prevent one additional bad outcome
equation for NNT
In studies it is calculated by 1 / (EER - CER)
i.e. NNT = 1 / ARR
what is meant by relative risk
RR = Probability of an event when exposed/Probability of event in control group
Also called risk ratio.
measure of proportionate increase in exposed group
RR = EER / CER (= (a / a+c) / (b/b+d) )
what is meant by absolute risk?
Absolute risk is likelihood of developing a disease over a time period
what is meant by hazard ratio
A hazard ratio considers your absolute risk to be 1.
If something you do / take doesn’t change your risk, then the hazard ratio is 1.
If something you do lowers your risk by 30% compared to not doing it then that action makes your hazard ratio 0.70 = the risk is 70% of what it was (30% lower).
If something you do triples your risk, then your hazard ratio is 3.0 (risk is 3 times greater than it was before).
Experimental event rate calculation
EER = a/ (a+c)
a = exposed and diseased c = exposed and not diseased
A measure of how often a particular event occurs within the experimental group of a trial.
what is the Absolute risk reduction
ARR (RD) = CER - EER
i.e. (a/a+c) / (b/b+d)
absolute risk reduction is the same as risk difference. Comes from subtracting the risk in one group from the risk in the other group.
High risk patients show a bigger risk difference than low risk patients. Patients who are unlikely to experience the outcome will need more patients to be treated for one outcome to be avoided, and the risk difference is smaller.
what does it mean if the relative risk is 1
no risk difference
no causation
what does it mean if the relative risk is > 1
Increased risk amongst those exposed
i.e. it is a risk factor
what does it mean if the relative risk is < 1
decreased risk amongst those exposed
i.e. it is a protective factor
what is relative risk reduction
Relative risk reduction is the proportional reduction in risk between active and control participants in a trial.
If the relative risk reduction is 10%, the risk in the active treatment group will be 90% of that in the control group.
what makes the NNT larger?
Less effective treatments
i.e. prevent fewer events, so more patients need to be treated to prevent a single event.
what makes NNT smaller?
The NNT gets smaller for longer durations of treatment.
Or for more effective treatments
Which will appear more impressive of the relative risk or the absolute risk?
The relative risk will always be a larger percentage figure than absolute risk, so relative risk seems more impressive.
What impact does the framing of research results have
The framing of results is the way that results are presented and this can influences doctors’ attitudes about a treatment.
what is EER
EER = experimental event rate (incidence in group receiving intervention) EER = a/ (a+b)
what is CER
CER = control event rate (incidence measured outcome in control) CER = c / c+d
What is meant by odds ratio
Odds Ratio is a method of comparing how likely events are between 2 groups.
odds of event occurring in one group divided by the odds of event occurring in the other group.
OR = a x d / b x c
calculation for odds of a positive outcome in exposed patients
odds f a positive outcome in exposed patients = a/b
e.g. odds of rolling a 1 on a dice = 1/5 = 0.2
what is a Student’s t-Test
Students T-test compares two means (averages) and tells you if they are different from each other.
And how significant the differences are.
what is Chi Squared test
Chi Squared test is a
Nonparametric test used to compare numerical or categorical data sets.
what is categorical variable
ategorical variables represent types of data which may be divided into groups.
Examples of categorical variables are race, sex, age group, and educational level.
what is meant by Nonparametric data
Does not fit a normal distribution.
Nonparametric statistics uses data that is often ordinal, meaning it does not rely on numbers, but rather on a ranking or order of sorts.
e.g. a survey conveying consumer preferences ranging from like to dislike would be considered ordinal data.
what is a numerical / quantitative (Non-categorical) variable
Numerical (Non-categorical) variables are usually referred to as range variables and are expressed as numbers within the set of the Reals, usually varying from negative infinity to positive infinity