Suppose it is your job to monitor the water quality at the local beach and to determine whether it contains high levels of certain bacteria. If there were high levels of bacteria the water may not be safe to swim in. However, the beach is very large and it is not possible to monitor the entire swimmable area of the beach.

[Continued from the previous question]

Suppose it is your job to monitor the water quality at the local beach and to determine whether it contains high levels of certain bacteria. If there were high levels of bacteria the water may not be safe to swim in. However, the beach is very large and it is not possible to monitor the entire swimmable area of the beach.

One day you go down to the beach and collect water samples from 10 randomly selected areas. You estimate that the average level of bacteria is 10 parts per million. On the same day, a colleague of yours conducts an independent data collection and collects her own 10 samples from the same general area. She estimates the level of bacteria to be 12 parts per million.

What would be a likely explanation of the different estimates obtained by you and your colleague?