To ensure that your results are valid, consider the following guidelines when you collect data, perform the analysis, and interpret your results. 
 
 
 
- The response should be numeric
  
- To calculate the mean response at different factor levels, variability charts require numeric response data.
 
 
 
- You can have up to  8 factors
  
- You can have up to eight numeric, text, or date/time factors. Each factor should have at least 2 levels.