Why is the frequency of induced mutation higher than in spontaneous mutation?

Mutations are an interruption in the normal sequence of DNA within an organism.  Mutations have traditionally been of the spontaneous variety, occurring naturally in nature over the vast expanse of time.  The normal time line can be quite long, so spontaneous mutations occur at a much reduced rate than do induced mutations.  Induced mutations are those caused by scientists in a controlled laboratory setting.  They occur at the direction of the scientist, when and where...

Mutations are an interruption in the normal sequence of DNA within an organism.  Mutations have traditionally been of the spontaneous variety, occurring naturally in nature over the vast expanse of time.  The normal time line can be quite long, so spontaneous mutations occur at a much reduced rate than do induced mutations.  Induced mutations are those caused by scientists in a controlled laboratory setting.  They occur at the direction of the scientist, when and where he or she directs.  So the frequency at which the induced mutations occur would naturally be higher than that of the spontaneous mutations, which might take a very long time to occur.  Mutations may be a substitution, where a nitrogenous base is substituted for another, or an addition, where an extra base is inserted within the genetic code.  A deletion is where a base is pulled from the existing DNA sequence, without inserting another.