# Trials

A trial (or experiment) is a series of runs of the simulation, performed with the same settings for all parameters other than “random numbers”. As the simulation is intended to resemble real life scenarios (i.e. with variability), it is important to run a simulation more than once. A trial gives you more rounded results and improves accuracy in terms of proposed performance measures (results).

The purpose of a trial is to check the reliability of results. At the end of just one run you have simulated one week in your organization. You have a result that is from one week. Just like real life, that could have been an average week, or a bad week, or a good week. We have no way of knowing what sort of week it was unless we run a few more of them.

A trial is a run of several weeks and the trial results summarize the results of these several weeks.

### Confidence Intervals

When you run a trial your KPI summary results are displayed as confidence intervals rather than just single numbers.

The central column of figures gives the result averaged across the weeks in the trial. This gives a guide as to what we expect the long term average to be (if we had time to do 1000's of runs).

The left and right columns give you some indication of how reliable the central (average) figure is. In some cases the average figure may be very reliable because, perhaps, there is little variation from week to week, on the other hand, it may be less reliable, and you need to know if this is the case. For example, an average of 50 when alternate weeks swing from 0 to 100 is very different from an average of 50 when they vary only between 49 and 51!.

The left and right columns give a prediction of the range that the average figure will be. Because simulation is a predictive method, that includes the variability that is in real life, if is never possible to be 100% accurate. These left and right figures give the range that the long term average will be on 95% of times the prediction is made. 80%, 90%, 98%, 99.8% and 99.9% limits are available by right clicking the mouse on where it says either Low 95% Range or High 95% Range

The more runs you do in a trial, the more accurate the predictions will become.

Although providing a range for a result may seem more vague than providing a single number it's actually far more accurate. Any simulation professional would advise you to always use trials to be certain.