Stratified Sampling
Robert P. Connolly [1] |
Stratified sampling is a strategy in which a heterogeneous population is divided into smaller, more homogenous subsets (“strata”). Each sampling stratum is then sampled independently using the simple random strategy. For this example, the sampling strata will be the 7 areas of the Poverty Point shown on the map below: the North ridges, Northwest ridges, West ridges, Southwest ridges, South ridges, Outside (the ridges), and the Plaza. Here again you will draw a 6% sample (16 squares). You will select 2 squares each from the North, Northwest, Southwest, South, and Outside sections, and 3 squares each from the West and the Plaza sections (since these two areas are larger). |
Instructions:
- Click on the random number
button to generate a random number between 1 and 247.
- Then find the number on the grid, and click on that
square.
- A star will appear if there are artifacts in that square and dirt will appear if there are no artifacts.
- As you click on a square, you will see the number of objects found in that square appear below the map.
- Record the artifacts foundon the Raw Data Table as the information appears.
- If you are using the excel sheet, save often.
- As you uncover the squares below, only
uncover 2 squares each in the Outside, South, Southwest,
Northwest, North sections, and 3 squares each in the
West and Plaza sections.
- If you generate a number that
you don't need, simply click on the button again to
generate a new random number.
- If you generate a number that
you don't need, simply click on the button again to
generate a new random number.
- Repeat clicking on the random number button
and the matching squares untill you have uncovered
16 squares.
- Continue on to the next page to view the results of a larger sampling rate (12%), and then answer the questions at the end of the activity.
Things to Know:
- Make sure that every time you click within the grey box below you are
clicking on a square in the grid to uncover the artifact. If you click
somewhere else within the grey box before all 16 squares are uncovered,
you will need to hit the reset button to uncover enough squares.
- Hitting the reset button or navigating away from the page will cause all the data on this page to be lost. Make sure you record your data before you do this.
- If for any reason you cannot uncover all 16 squares (i.e. if you accidentally click too many times), simply hit reset and uncover the remaining squares you need.
Time: 20-25 mins.
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