sampling

• what is an opportunity sample?


  when participants are chosen because they are available eg. university students selected because they are around at the time
• what is a self-selected sample?

  when participants are invited to participate eg. through advertisements via email or notices - those who reply become the sample
• what is a snowball sample?

  from a very small number of participants, more are contracted through the initial group
• what is a random sample?


  when all members of the population (possible participants) are allocated numbers and a fixed amount of these are selected in an unbiased way eg. taking numbers from a hat
• what is a stratified sample?

  when all types of members of the population are represented by deliberately selecting participants in proportion to their existence in the population
• strengths of an opportunity sample?

  quicker + easier than other methods as participants are readily available
• strengths of a self selected sample?

  relatively easy as participants come to you and are committed which decreases drop out rate
• strengths of a random sample?

  relatively easy as you only have to find the first few + is a convenient way to find a sample of a particular kind of participant
• strengths of a random sample?

  should be representative as all types of people in the population are equally likely to be chosen
• strengths of a stratified sample?

  should be representative as all types of people in the population are represented
• weaknesses of an opportunity sample?

  non representative as the kind of people available are likely to be limited and therefore similar - making the sample biased
• weaknesses of a self-selected sample?

  non representative as the kinds of people who respond to requests are likely to be similar eg. have free time
• weaknesses of snowball sample?

  non representative as they are likely to be similar in ways other than any other common characteristics needed for the study
• weaknesses of a random sample?

  hard to ensure everyone is equally likely to be chosen due to lack of information or access + sample may be biased eg. if only girls are selected - especially if the sample is small
• define instantaneous scan sampling?


  when the action performed at the start of each interval is recorded
• define one-zero sampling?


  observer records whether behaviour occurs during the time period