However, in random sampling, these five 20-minute periods may be distributed randomly over the course of the day. That is to say, intervals between observation periods could vary—some longer others shorter. One point I'd like to make is systematic and random time sampling are not always used in isolation. They are often combined in studies.For example, while observation intervals are scheduled systematically, observations within an interval are made at random times. That means the researcher might decide to observe only during 15-second intervals that are randomly distributed within each 20-minute period. Now let's come to situation sampling. Then, what is situation sampling? It involves studying behaviour in different locations and under different circumstances and conditions. By sampling as many different situations as possible researchers can reduce the chance that their observation results will be peculiar to a certain set of circumstances and conditions. Why? Because people or for that manner animals do not behave in exactly the same way across all situations.