Surveys that use sampling only gather data from a small part of the total population. If the sampling is truly random, then the data gathered is usually representative of the larger population. This means that if there are 10 times as many bluegill as walleye in the lake, then a representative sample will find 10 times as many bluegill as walleye in the nets.

But sampling is not a perfect way to gather representative  data. Depending on the day, weather, and location of the nets, the types of fish caught may change—and those changes may affect the data analysis.

Look at the two pictures on the left. Each lake contains the same population of blue and red fish, but the two samples are slightly different. This shows that population sampling is good for estimating, but not always a good way to gather complete data.

Which sample is more representative of the whole population of red and blue fish in the lake? How do you know? And what does this example tell you about random samples? Explain your answer in three to four sentences.

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