In image processing and statistical analysis, to smooth a data sample is to produce an approximate function that tries to accurately capture key structural patterns in a data set, while not necessarily leaving out any fine-scale structure or other fast phenomena. By taking the mean difference between the original data set and the sample, or the difference of the difference between the original data and the mean, a smoothing function can be created that minimize the difference between the original data and the mean of the difference between the original data and the mean. The idea of minimizing the difference between the original data and mean is to reduce the noise level in the sample, and to make it so that the data is still as good as possible. For instance, if you have data from an experiment and a control where you just had ten trials and one control group where you had five trials, then the two data sets can be compared with respect to the amount of noise.

After finding the difference, the smoothing algorithm determines the most effective way to remove the excess noise by removing the smallest values in a sample, or by calculating a curve that reduces the largest values in a sample. The value is then compared to the original data and is adjusted in some manner to make it more similar to the original data. The more similar the value is the more accurately the original data was smoothed and minimized.

If a normal curve is chosen for smoothing the data then the smoother must choose a point on the curve that gives the best result. There are many different ways in which to determine a curve to use in smoothing, including least squares fitting of the curve against the original data. The curve must be chosen such that the mean difference and standard deviation (or variance) of the data and the curve are equal, otherwise the curve may actually minimize the difference and thus will not minimize the variance, resulting in an inaccurate estimation of the average difference. The data must also be linearly independent and the slope of the curve must be not more than about a third of the original data.

A curve is typically chosen using a Monte Carlo procedure, using random data to find the curve to use. The random data used in this procedure is chosen according to the prior assumption that there is no correlation between the data and the curve, that there is no correlation between the control and random data, and that there is no non-stationarity in the curve. {which means that the slope does not change when the sample size changes. {i. If there is a correlation between the two samples then the relationship between the curves cannot be properly determined and therefore the curve can not be chosen as a smoothing curve, or a curve can not be chosen. {, as a smoothing function. at all.

While using Monte Carlo smoothing techniques to calculate the smoothing curve it is important to use the proper choice of the curve, as if the chosen curve has a higher value than the original data then the final smoothed data may contain too much noise. Using a lower value curve will eliminate some of the unnecessary noise that may have accumulated in the data in the process, but will also create a smoother appearance, and a smaller sample size.

It is very important that the data be tested for non-stationarity prior to being used in smoothing, and that the test should be repeatable for other tests, because if there is a large number of repeated tests then the test will become quite costly. Most statistical applications that require smoothing will require the use of multiple smoothing tests and most other statistical tests will also require repeated tests on the same data.