An increasingly important aspect of public health is the safety of
the food supply.
A research team studied the effect of irradiation on the
bacterial content of raw beef. The beef was irradiated for a certain
length of time, and then the bacterial content measured either 3 days
or 7 days after irradiation. Ten batches of ten-pound portions of beef
shoulder meat were obtained, and each batch was then divided
into ten one-pound portions. Within each batch, each one-pound portion
was randomly allocated to one of the ten treatments: the combination
of irradiation duration (0, 15, 30, 45, or 60 seconds) and
days after irradiation (3 or 7) for measurement of bacterial content.
The portions were refrigerated at 35 degrees F during the 3 or 7 days.

Bacterial content units are counts divided by 10^2.
Columns are batch, days, duration, and bacteria.