What is Visual Rx?
Visual Rx is designed to calculate Numbers Needed to Treat (NNT) from the pooled results of a Meta-analysis and produce a graphical display of the result.
The idea was born out of empirical work which I presented at the Seventh annual Cochrane Colloquium in Rome in October 1999. There are many different statistical methods which can be used in calculating a summary estimate from the results of individual clinical trials and NNT can be calculated in different ways from each of these. Since the results are not always identical Visual Rx is designed to allow a variety of methods to be used. In order to try to make the concept of NNT more understandable to clinicians and patients Visual Rx produces a graphical display representing the likely outcomes for a theoretical group of 100 patients who are given a particular treatment.
Please note that the display will not represent fractions of a patient so is not suitable to demonstrate treatments where the NNT is greater than 100. The calculated NNT will still be correct however.
Visual Rx is particularly useful in relation to the results of Cochrane Systematic Reviews which are presented on the Cochrane Library. The summary of analyses can be reached for an individual review on the Library by clicking on the Outline button above the text of the review and selecting Summary of Analyses from the drop-down menu. Follow the blue hypertext link in the text of the review by clicking on it and then the data can be found for each outcome by double-clicking on the individual lines on the summary screen.
NNT can only be calculated for dichotomous outcomes (marked on the summary screen as a blue box) and initially the results are presented as a Peto Odds ratio which is shown at the bottom right corner of the display with its 95% confidence interval in brackets. This pooled Peto Odds Ratio can be entered into Visual Rx, together with the desired control event rate. This may be the total at the foot of the control arms of the included trials (which is the pooled control event rate) or may be a different figure from other studies to represent specific groups of patients.
Other statistical methods are available in the Cochrane Library and can be selected by clicking on the Statistics heading on the toolbar at the top of the Metaview screen. To use other summary statistics click on the arrow to the right of the Peto Odds Ratio box and then select from the drop-down menu. Not all methods are equally reliable and you may wish to consult the help files before deciding which summary statistic to use.