SS - Sampling Methods Lesson

Sampling Methods Lesson

Random Sampling

Random sampling means that an unbiased strategy was used to select the participants in the statistical investigation. Random assignment of treatments means that a strategy was used to determine who gets an active treatment and who gets a placebo or the order in which treatments are given. In both situations, we can use a random number table or generator to select participants. There are several different types of random number generators including your graphing calculator.  Refer to your calculator manual or do an online search for "random number generator."

Read the chart below to learn about the different types of sampling techniques.

An graphic showcasing five types of statistical sampling methods. Simple random sampling with icons of individual figures and text stating ‘members are randomly chosen’; Stratified random sampling with grouped icons by color and text ‘members are first grouped based on members’ shared attributes or characteristics and then each subgroup is randomly sampled from’; Systematic sampling with a line of figures and one highlighted with text ‘members are chosen according to every 3rd person point etc.’; Cluster sampling with groups enclosed in circles and text ‘members are divided into smaller groups (not based on shared attributes) and the whole group is randomly selected’; Convenience Sampling with scattered figures and a hand selecting some, accompanied by text ‘nonprobability samples in which people are sampled simply because they are “convenient” sources of data’

Margin of Error

1Margin of error is information that’s provided alongside the results of a piece of research, such as a poll, survey, or a scientific study. You’ll recognize it because it’s expressed with a plus and minus sign together, e.g. + or -1%

Researchers use this to provide additional information that helps you interpret their results and to understand how the study was carried out. The figure tells you that the true result may differ from the percentage figure provided, and how much more or less than the stated percentage the reality might be.

Margin of error provides a clearer understanding of what a survey’s estimate of a population characteristic means. A plus or minus 2 percentage points means that if we ask this question using a simple random sample 100 times, 95 of those times it would come out at the estimated value plus or minus 2 points.

The larger your random sample (the more responses you get), the smaller your margin of error will be and the more confidence you’ll have that your sample results are reliable.

2As an example, a poll might report that a certain candidate is going to win an election with 51 percent of the vote. Plus, the confidence level is 95 percent and the error is 4 percent. If we assume that the poll was repeated using the same techniques, then the pollsters would expect the results to be within 4 percent of the stated result (51 percent) 95 percent of the time. In other words, 95 percent of the time they would expect the results to be between:

  • 51 – 4 = 47 percent and
  • 51 + 4 = 55 percent

 

Self-Assessment: Billboard Hot 100

Go to Billboard Hot 100 Links to an external site.and select the Hot 100. This list gives the top 100 songs for the week. You will compute statistics on the number of weeks that a random selection of the songs has been on the charts. (If you wish, choose one of the specialized charts such as R&B/Hip-Hop or Country.)

  1. Use your calculator or a random number generator to select 10 of the 100 songs.
  2. Write down the name of each song, its rank on the list, and the number of weeks it has been on the chart. For example, if your random number generator gives you 3, write "No. 3, Mary Had a Little Lamb ̧14 weeks."
  3. Calculate the descriptive statistics for the data set and interpret all statistics.
  4. Use a different tool to select 10 of the 100 songs.
  5. Write down the name of each song, its rank on the list, and the number of weeks it has been on the chart. For example, if your random number generator gives you 3, write "No. 3, Mary Had a Little Lamb ̧14 weeks."
  6. Calculate the descriptive statistics for the data set and interpret all statistics.

What did you discover? What's the average number of weeks that a random selection of the songs has been on the charts.

1Your Guide to Margin of Error (With Calculator). (2022, August 24). Qualtrics. Retrieved October 14, 2022, from https://www.qualtrics.com/experience-management/research/margin-of-error/

2Margin of Error: Definition, Calculate in Easy Steps. (2022, April 18). Statistics How To. Retrieved October 14, 2022, from https://www.statisticshowto.com/probability-and-statistics/hypothesis-testing/margin-of-error/

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