Final answer:
It may not be feasible to use a probability sample in public places due to the difficulty in constructing a sampling frame of interactions. Convenience samples can introduce biases and limit external validity, but they are often used due to practical constraints. The use of random sampling is effective for its ability to reduce selection bias, although its feasibility depends on context.
Step-by-step explanation:
It may not be possible to use a probability sample to observe behaviour in public places because it is not feasible to construct a sampling frame of interactions. In public settings, there are challenges in defining and accessing the population of interest for a truly random sample. Situations such as observing behavior in highly private or sensitive contexts, like prisons or clandestine organizations, further complicate the matter. Naturalistic observations in public places may require methods that offer researchers the ability to remain unobtrusive or to use convenience samples that, while not random, are more practical to obtain.
Using convenience samples, like students in Introduction to Psychology courses, has implications such as potential biases and limits to external validity. While convenience samples offer easier access and may be more feasible in terms of cost and time, there's a trade-off in that the sample may not be representative of the population at large. Additionally, observational research can be impacted by observer bias, and it is essential to establish criteria and ensure inter-rater reliability when recording behaviors.
The choice to use a random sample, where each member of the population has an equal chance of being included in the study, is an effective method because it strives to minimize selection bias, thereby enhancing the representativeness and validity of the findings. However, the appropriateness of sampling techniques is heavily dependent on the research question, context, and ethical considerations.