You will find Video 3: Sampling by navigating to the MSL Tools for Success link under Course Home. This video discusses sampling in the context of how estimates of population parameters are obtained. It refers to Video 1: What is an Average? where we obtained an “average of 1.89 feet per person.” It points out that applying this statistic depends on thinking through whom the population is meant to be, and that depends on the study question (i.e., “If you want to understand your answer, you really have to work out carefully what your question is.”).
As the sample statistic was derived from a bunch of kids heading to the playground, plus a one-legged man who we asked to show up, we conclude that the sample was a bad one. We explain that random sampling is generally a good way of obtaining a representative sample such that you can be confident that the sample statistic is a good estimate of the population parameter.
Respond to one of the following questions in your initial post:
- Are all good samples random? This is an opportunity to bring up opinion polling, which typically tries to obtain views from particular groups (e.g., men, women, older, younger, employed, unemployed, Democrat, Republican, etc.) and then “weights” the results by the prevalence in the population.
- Magazines often report surveys giving statistics such as “63% of women expect the man to pay on the first date.” Are these random samples? These surveys are most definitely not random – they are typically click-through from the magazine website – and so can provide an opportunity to discuss the sort of biases that can result from lack of random sampling.
Your initial post should be 150 to 250 words in length. Respond to at least two of your classmates’ posts by Day 7 in at least one paragraph.