Cross-validation can be done once (10 times, or simply
10), or done ten times (10 times done 10 times, or
10 x 10). For clarity, let's change these values to
5 x 20. Here's how this works:
- The training set is randomly partitioned into five chunks.
- Five models are built out of these five. Each model is built using four of the chunks as a training set, and one as a testing set.
- The five models are averaged to create a single model balanced for randomness.
- To account for the initial choice of the five partitions, we repeat steps one through three 20 times. The resulting 20 models are averaged.
Steps 1-3 constitute cross validation, which is the
10 you're asking about, or the
5 in the example. Step 4, which repeats steps 1-3, is repeated portion of repeated cross-validation and the
x 10 you're asking about, or the
x 20 in the example.