Measurements were taken on almost 200 chicks in these rooms. It is possible to think of the experiment as having chicks (or eggs) randomly assigned to the rooms, and to consider the sample in each room as a random sample from a population of chicks exposed to that environment (combination of temperature and presence or absence of mycoplasma bacteria). This experiment on bird development was conducted in two runs separated by several weeks. Several things could have changed in that time, including the mycoplasma culture, seasonal changes of chick growth and food or water conditions. The scientist inoculated eggs in the first run, but decided to switch to inoculating young chicks in the later run. Earlier analysis in the text has assumed that inoculation could be just considered as another factor. Here it is viewed as a blocking factor with no replication. That is, strictly speaking it is not possible to assess the main effect of inoculation method since there is no replication of runs. However, it would be possible to assume that interactions with run were interactions with inoculation.