Precision estimates of treatment effects Flashcards
What is evidence based practice?
Treatment decisions based on:
- Clinical expertise
- Preferences of the patient
- The best available evidence
How do we use samples for research?
We use samples to provide estimates of population parameters
Most research is done on a snap-shot of population:
- Sample is drawn from a larger population of interest
- Sample tells us something about the population (ie all people to whom were are trying to make inferences about)
What is sampling bias?
Sample is selected in such a way that the individuals chosen are not representative of the whole study population
How do you work out the 95% reference range on a data graph?
Data within 2 SD of the mean
Why do we use it/need it? - tells us about the ‘typical range’ as there is only 2.5% at the top and the bottom that isn’t included
Need to understand that there is uncertainty in everything we estimate from data / measurement, a confidence interval is a measure of statistical uncertainty or “precision”.
What is the connection between accuracy and precision?
Accuracy is to do with getting the right answer – avoiding bias
Precision is to do with inherent error associated with any estimate
What are confidence intervals?
The spread of ‘estimates’ or ‘means of something of interest’ is defined by the 95% confidence interval
**reference range is usually large, it is 95% of the data. Confidence interval is a very small range ie. 132-133mmHg
How do you work out the standard error of a study sample?
SE = SD / square root of the number of samples
Therefore the confidence interval is = mean +/- 2 x SE
…and this is what tells us is the TRUE MEAN compared to the reference range
- eg. it gives us a guide as to how precise we are about the probibility
How are confidence intervals useful in medicine?
Evidence in medicine relies on research data that is precise
- confidence intervals are a measure of precision
How do you compare groups using a ratio estimate?
- generally used to compare risks between groups
How do you compare groups using absolute difference?
what is the difference between a 95% reference range and 95% confidence interval?
