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Activity: Sampling Design

Materials

  • Small colored objects in a bag
  • Sampling tool (e.g. spoon)

Procedure

  1. Write down all of the different colors that are in the bag. If you cannot see into the bag, use your prior knowledge to come up with a list of the possible colors of the objects inside.
  2. Make predictions about the colors of objects in the bag.
    1. Which color(s) do you think are most abundant? 
    2. Which color(s) do you think are least abundant? 
  3. Using your predictions, develop and record a hypothesis about the colors of objects in the bag. 
  4. Each person will be taking a sample of objects from the bag.  Develop a standardized sampling scheme considering the following:
    1. How many objects should each person collect?
    2. What will be used to collect the samples?
    3. How will samples be removed from the bag?
    4. How will you ensure that the sampling is random?
    5. What will you do if a person takes a sample that is larger or smaller than the size determined by the class?
  5. Using the procedure developed by the class, sample the bag.  Each member of the class should take one sample. Complete Table 2 with the colors of objects you sampled, the total number of each color, the total number of all the colors together, the fraction of each color compared to the total, and the percent of each color compared to the total. 
     
    Table 2. Individual sample data table
      Color Total
               
    Number              
    Fraction of Total              
    Percentage of Total (%)             100%

     

  6. Based on your individual sample, 
    1. What can you infer about the colors in the bag?
    2. How do you think your sample may compare to other people’s samples? 
  7. Record three samples from any three class members on a class data table. Table 3 is an example data table; you can modify the number of color columns and rows based on your class. 
  8. Based on the first three samples shared by the class,
    1. What can you infer about the colors in the bag if data collection stops at this point? 
    2. What might you observe as we add more samples to the data table? 
  9. Record the remaining samples on the class data table.  For each color, determine the average, fraction of total, and percentage of total.
Table 3. Class colored object sample data table
  Color Total # of objects sampled
           
Sample Number              
1              
2              
3              
4              
5              
6              
7              
8              
9              
10              
11              
12              
13              
14              
15              
Total              
Average              
Fraction of Total              
Percentage of Total (%)              

 

 

Activity Questions: 

 

  1. What did you learn about the composition of the bag by collecting data on your individual sample?
  2. What did you learn about the composition of the bag by compiling and averaging class data?
  3. How did your individual data, the first three points of class data, and the entire set of class data compare? Explain.
  4. Ask your teacher to share the known proportion of each color of object in the bag. How did the averaged class data proportion of colors compare to the known proportion of colors? Explain why you think this occurred.
  5. What would result in your sample data if you picked your favorite colors out of the bag when sampling? 
  6. What situations in nature might cause individual samples not to reflect the larger area? 
  7. What would happen to your sample data if there were just one or two objects of a particular color in the bag?
  8. Read Practices of Science: Scientific Error.
    1. What are the sources of error in this sampling activity? 
    2. How well do you think your sampling procedure controlled for bias? Explain.
 
 
 
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.