Time sampling means that researchers choose various time intervals for their observation. Intervals may be selected systematical

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问题     Time sampling means that researchers choose various time intervals for their observation. Intervals may be selected systematically or【T1】______. Suppose we want to observe students’ classroom behaviour. Then in systematic time sampling, our observations might be made during five 20- minute periods,【T2】______. The first observation period could begin at 9 am, the second at 10 am and so forth. 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 【T3】______—some longer others shorter. One point I’d like to make is systematic and random time sampling are【T4】______. They are often combined in studies. For example, while observation intervals are scheduled systematically, observations within an interval are made 【T5】______. That means the researcher might decide to observe only during 【T6】______that are randomly distributed within each 20-minute period.
【T6】

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答案15-second intervals

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