All this while, we assume that we know some of the population proportion p. However, in reality we do not know the population proportion, which is why we conduct experiments to try to find it.

However, conducting experiments is not feasible (refer to 4.1 Concepts of Population and Random Samples). This means that p is unknown, since we cannot conduct experiments to find it out.

Therefore, we use random sample(s) instead, which gives the sample proportion(s) \hat{p}. Value(s) of \hat{p} gives some indication of the value of p, and can be used when we have no other information.

The value of \hat{p} (from a single experiment) can be used to estimate p. Since this is a single-valued estimate, it is called a point estimate of p.