The following diagram illustrates manuscript corruptions in the Biblical texts that are produced, for whatever reason, and copied down to later manuscripts. The purpose of the illustration is to show how errors are copied down from one manuscript to another, how they are counted, and how we can determine which is the correct reading.
In this example of the 26 existing manuscripts (represented by solid black and red sheets), nine of them have a textual problem where a phrase was incorrectly copied. Therefore, in this illustration, we would have a total of nine variants in 26 manuscripts. But, it is really only one.
However, manuscripts can be categorized in family trees by analyzing their location of discovery, jars found in, type of papyri written on, type of ink used, style of writing, etc. Therefore, daughter manuscripts can be matched very accurately to father manuscripts.
In this example, we see that the word "only" was omitted from a 3rd century document and copied in subsequent, daughter documents. All we need to do is to take a look at the manuscripts, and even though we see nine variants here, actually we can tell that there is only one which has been copied. Also, we can accurately determine which is the correct reading by looking at the father document from the 2nd century.
With this type of method, the New Testament documents can be reconstructed with an incredible accuracy. Furthermore, the New Testament is approximately 99.5% textually pure. This means that of all the manuscripts in existence that they agree completely 99.5% of the time. Of the variants that occur, mostly are easily explainable and very few have any effect on the meaning of passages. In all, no New Testament doctrine is affected by any variant reading.