Mutations are an interruption in the normal DNA sequence within an organism's genome. Mutations have occurred naturally over millions of years of development within organisms as they progress historically. These naturally occurring mutations are called spontaneous mutations, meaning they were random, "luck of the draw" changes in the genome of specific organisms. The frequency, or how often these mutations occur, is spread out over a long period of time.
Scientists wanting to study mutations in a specific genome may induce mutations, using a controlled lab setting, which will cause the number of mutations per unit of time, or frequency, to increase. Scientists induce mutations so they can study more effects in a shorter period of time. They induce these mutations by using a mutanizing agent, such as radiation, chemical, or transposon insertion. Any of these techniques will cause a point substitution, deletion, or addition in the normal genome of an existing organism's genetic sequence.
So the frequency of scientific induced mutations is higher than that of natural spontaneous mutations because induced mutations are generated by scientists in laboratories for scientific purposes and therefore can occur at an accelerated rate.