# Simple Random Sampling ✓¶

Selecting a sample by simple random sampling requires you to specify the study area and a sample size.

- Start by running the Sampling Design script in the Scripts pane.
- In the first entry box
*Specify an image ID and sampling scheme*, specify a map that defines the study area. Because you are not using strata or clusters, the contents of the map does not matter. - Under
*Specify band if a multi-band map (if not, specify 1)*: if you are using a map that contains multiple bands, specify which band you want to use to define the study area. Otherwise, just specify “1”. - If the map has a no-data value or if you want to exclude a certain value in the map when defining the study area, specify the value in
*Specify no data value*. - Click
*Load image*– the map should be displayed in the image pane. - Under
*Select a sampling scheme*, select*Simple Random* - Under
*Determine sample size*, you can either specify an arbitrary sample size or determine the sample size by specifying a target standard error of the anticipated overall accuracy of the map that is being assessed.

- If specifying arbitrary sample size
- If choosing to specify an arbitrary sample size, simply add a number under
*Specify sample size*. - Click
*Create sample*.

- If choosing to specify an arbitrary sample size, simply add a number under
- If specifying a target precision
- To determine the sample size required to meet a certain target standard error of the overall accuracy, first specify the anticipated overall accuracy of the map you are assessing under
*Specify anticipated overall accuracy (0-1)* - Then
*Specify target standard error of overall accuracy (0-1)*and click*Calculate sample size*– the sample size is calculated using Equation 12 in [1] which is derived from Equation 4.2 in [2]. - Click
*Create sample*.

- To determine the sample size required to meet a certain target standard error of the overall accuracy, first specify the anticipated overall accuracy of the map you are assessing under

- To view, the sample in the Display pane, click
*Add to map* - To export the sample, click
*Export sample*and select the desired file format.

[1] | Olofsson, P., Foody, G. M., Herold, M., Stehman, S. V., Woodcock, C. E., & Wulder, M. A. (2014). Good practices for estimating area and assessing accuracy of land change. Remote Sensing of Environment, 148, 42-57. |

[2] | Cochran, W. G. (1977). Sampling techniques. John Wiley & Sons. |