What's New 2008 Version?
Visual Rx version 3 has several improvements. It is now possible to save and print the graphical displays of faces (now referred to as Cates plots) more easily. The user also has the choice of generating a plot with 100 or 1000 faces, and Visual Rx has two new outputs in the form of a sentence summarising the effect of treatment, and a table of natural frequencies. The table uses the control event rate entered by the user and calculates the expected event rate with treatment. The duration of treatment should also be specified when entering data (as absolute treatment effects are time dependent).
In the 2004 Updated version of Visual Rx the Confidence Interval (CI) for the calculated Number Needed to Treat (NNT) can be generated by entering the upper and lower CI for the Odds Ratio or Relative Risk on the data entry screen. The CI for the NNT will then be displayed on the second smiley face screen. The rounding is always up to the next integer when calculating NNT (so 3.1 will round up to 4).
Using Visual Rx
This programme can change pooled data from Meta-analyses into absolute treatment effects to be applied to individual or groups of patients at known baseline risk. It is designed primarily for use with The Cochrane Database of Systematic reviews, but can also be used with pooled data from any meta-analysis. The data you will need to input into Visual Rx is found in the Forest plots in a particular Cochrane review. This screen can be reached by clicking on the Data & analyses link in the left hand menu for the individual review. Follow the blue hypertext link to the outcome that you want to use and the pooled result (with CI in brackets) is usually shown at the bottom of the screen.
TIP: NNT and other absolute treatment effects can only be calculated from outcomes that have been analysed as data that has counted the number of people who experience the event of interest. NNT cannot be calculated from data measuring the average size of events. For example "Hospital Admission" can be used, but not length of stay in hospital.
How events are recorded in Cochrane Reviews
Visual Rx can be used to calculate NNT from Odds Ratios and Risk Ratios in systematic reviews on the Cochrane Database, but it is designed to analyse data as ADVERSE EVENTS. Most (but not all) Cochrane reviews enter data about bad things that happen to people, but some report how well patients respond,
EXAMPLE: Reviews on smoking tend to report how many patients stop smoking (smoking cessation). This is a good event as smoking is damaging to health.
WARNNG: Visual Rx can convert data from Reviews reporting beneficial events such as smoking cessation, but ONLY USING THE ODDS RATIO. Relative Risks will give different answers when beneficial events are used and the baseline risk varies.
Entering Data into Visual Rx
When you checked that the data from the outcome are recorded as adverse events, then you can proceed to enter the data.
This is a free text field that you can use to label the graphical display of NNT generated by Visual Rx.
The outcome of the intervention should be entered in this box. Please describe the outcome in terms of adverse (not beneficial) terms. If the outcome in the review is beneficial (such as survival or stopping smoking) please enter the adverse event in this box (mortality or continued smoking), and uncheck the adverse events box lower down. This allows the sentence generated by Visual Rx describing the results of the treatment to read correctly.
The absolute effect of treatment varies with the duration of treatment, so a duration should be entered which relates to the risk of the patient under consideration, or to an average duration from the trials (which might be a weighted mean or median duration).
Control Event %
The next data field is for the control event rate (expressed as a percentage risk). This can be entered directly from the data displayed on the Forest plot, or tailored to the risk of an individual patient. Initially you may wish to use the overall risk in the control arms of the trials included in the review. This is the sum of all the events in the control groups (in all trials) divided by the total patient numbers in control groups in all trials. However this may not be the best way to assess the baseline risk of a particular type of patient, as it depends on the size of the included trials and will be heavily influenced by the largest trials.
The percentage risk should be entered into this box on Visual Rx (e.g. a risk of 18% is entered as 18 in the first box).
Note: This pooled CER is dependent on the characteristics of the patients entered in each trial (amongst other things) and you may need to adjust this using other information to estimate the baseline risk of a particular patient group before calculating the absolute treatment effect for that group. If you want to change the baseline risk return to the data entry screen and put in a new control event rate (the Odds Ratio and CI will stay in the boxes), and then click ‘Calculate’ again.
The Odds Ratio is the default method for data entry into Visual Rx, but Relative Risk can be selected on screen if desired. Click on the arrow to the right of the method box on data entry screen and then click on Relative Risk to select it.
See section "Choice of Statistical Methods from a Cochrane Review" for more details on which method to use.
Number of Faces
Version 3 will allow a choice of 1000 or 100 faces to be shown, and this will also determine the natural frequencies shown in the table of results. The addition of 1000 faces is to allow rarer events (such as adverse events) to be displayed in a Cates plot. The default setting is 1000 faces, but for common events click on the drop-down menu and select 100 instead. This can be done after all the other data has been entered, and clicking on calculate will change the table of results and the appearance of the plots.
The pooled Odds Ratio may already be displayed on the Forest Plot on the Cochrane Database at the bottom of the column of results for each trial. You may need to enlarge the Forest plot screen or use the scroll bars to find it. The pooled Odds ratio should be entered into the Odds Ratio box on the data entry screen as a decimal (not as a percentage). For example 0.78 should be typed directly into the box.
The pooled result on the Forest Plot is presented with the 95% confidence limits in brackets and these should be entered into the boxes on the data entry screen for Visual Rx, again using a decimal point as above. When the Odds Ratio is displayed there is a further check box to show that the data has been entered as adverse events. If the data is recorded as beneficial events (such as cure) uncheck this box before proceeding.
To display the Cates plots, click on the Create pictures button. In Version 3 this will display plots showing the event rate in the control group, the sentence describing the effects of treatment, and below the line the changes with treatment.
The option to use Relative Risk can be selected by clicking on the arrow to the right of the Statistical Method box, and a drop-down menu allows Relative Risk to be chosen. The pooled effect can be entered in the same was as for the Odds ratio, as can the upper and lower confidence intervals.
There are two different Relative Risks for any outcome, an adverse event Relative Risk and a beneficial event Relative Risk. For rare events the Relative Risk and Odds Ratio will be similar, but for common events this is not the case. Visual Rx will therefore give different results depending on whether Odds Ratio or Relative Risk is chosen.
Since Odds Ratios give the same result for adverse and beneficial description of the outcome, this is the preferred method to use when entering data into Visual Rx.
Saving or printing the displays
This version makes it much easier to save or print the graphical outputs. By clicking on the blue hypertext link next the picture, a dialogue box opens to save the display picture onto your computer (in .png format). Note, the picture contains the key/legend but no description or title.
You can print both pictures at once and the accompanying descriptions and title by using your web broswers print facility, which is usually accessed by pressing File > Print.
The Graphical Display (Cates plot)
This display represents a total of 100 or 1000 faces that are divided into three categories. These can be thought of as if you were performing triage. The first screen shows faces that are either red or green. The smiling green faces are those patients who are free from harm (such as pain) with the control treatment. The red faces are those in pain with the control treatment. The baseline risk is described as a number out of 100 or 1000 in the first part of the sentence below the picture.
The second plot (shown below the line) demonstrates the effects of treatment. The smiling green faces are those patients who are free from harm (such as pain) with the active treatment. The red faces are those still in pain even with the active treatment. The middle group are the only ones that benefit from the treatment (and are shown as yellow faces). Since it is not possible which patients will benefit, all 100 or 1000 have to be given active treatment for this group to benefit.
If the treatment is harmful over all then there are no yellow faces but instead the crossed-out green faces are those harmed by the treatment for the outcome under consideration.
If you wish to assess the impact of treatment on patients at different baseline risks go back to the data entry screen , which will be open as a separate tab in your web browser, and put in a new control event rate. The results in the OR or RR boxes will stay as previously entered (including the upper and lower confidence intervals).
Visual Rx 3 needs to be used on-line, but the table of results and the summary sentence can be copied and pasted into a document or presentation, and the Cates plots can be saved or printed as described above.
It is envisaged that the programme will continue to be updated so please provide an email address to let you know when the next free update comes out.