resid vs fitted plot

[smorkoc]

                                      Plot of resid*Flux1.  Legend: A = 1 obs, B = 2 obs, etc.                                      
                                                                                                                                    
       resid |                                                                                                                      
             |                                                                                                                      
         0.4 +                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                  A                   
             |                                                                                                                      
         0.3 +                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                         A            
         0.2 +                                                                                A                                     
             |                                                                                                                      
             |                                                                                                      A               
             |                                                                     A                                                
             |                                                                                   A                                  
             |                                 A                                                                                    
         0.1 +              A                                                                 A                                     
             |                  A                   A      A   A         A              A          A         A                      
             |      A                                       BA                                                                      
             |       BA   A      A                 A   A       B       A                                                            
             |      A  A     A BA    AAB   A  A                    A                                                                
             |       AAAA    A A       B  AA           AA          A              A                                                 
         0.0 +      AC   B A             AAA                                         A           A                                  
             |       AA A AA   A              A                                            A                                        
             |       DA     A B A                  A A    B                                                                         
             |           A     A   B  A A A     A   AA  A                                   A                                       
             |                       A                                                                                              
             |         A A                  A    A                  A    A                                                          
        -0.1 +                                                    A                 A                                               
             |                                                     A                                                                
             |        A                                       AA                 A                                                  
             |                                                                                                                      
             |                                                              A                                                       
             |                                                                                                                      
        -0.2 +                       A                    A      A                                                                  
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                 A                                                    
             |                                                                                                                      
        -0.3 +                                                                                                                      
             |                                                                                                                      
             ---+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--        
              0.00           0.20           0.40           0.60           0.80           1.00           1.20           1.40         
                                                                                                                                    
                                                                  Flux1                                                             

here is my resid vs fitted plot, i was not sure it seems ok, could you help me? what should do next, if I face this type of plot.

[Reeza · Accepted solution]

What you're looking for:

• The residuals "bounce randomly" around the 0 line. This suggests that the assumption that the relationship is linear is reasonable.
• The residuals roughly form a "horizontal band" around the 0 line. This suggests that the variances of the error terms are equal.
• No one residual "stands out" from the basic random pattern of residuals. This suggests that there are no outliers.

Source: https://onlinecourses.science.psu.edu/stat501/node/277/

What you have:

• Residuals that are not bouncing randomly. They are lower around the lower values of flux and more spread out towards the higher end.
• No horizontal band, it's more of a funnel shape. 
• There are several residuals that seem problematic, one high up and one low down. 

Next steps:

1. Attempt to refit the model to see if another variable reduces the error. 
2. Transformation on variables to reduce variance
3. Something else, that makes sense given the contact of your problem which we only know a few things about. 

---

@smorkoc wrote:

                                      Plot of resid*Flux1.  Legend: A = 1 obs, B = 2 obs, etc.                                      
                                                                                                                                    
       resid |                                                                                                                      
             |                                                                                                                      
         0.4 +                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                  A                   
             |                                                                                                                      
         0.3 +                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                         A            
         0.2 +                                                                                A                                     
             |                                                                                                                      
             |                                                                                                      A               
             |                                                                     A                                                
             |                                                                                   A                                  
             |                                 A                                                                                    
         0.1 +              A                                                                 A                                     
             |                  A                   A      A   A         A              A          A         A                      
             |      A                                       BA                                                                      
             |       BA   A      A                 A   A       B       A                                                            
             |      A  A     A BA    AAB   A  A                    A                                                                
             |       AAAA    A A       B  AA           AA          A              A                                                 
         0.0 +      AC   B A             AAA                                         A           A                                  
             |       AA A AA   A              A                                            A                                        
             |       DA     A B A                  A A    B                                                                         
             |           A     A   B  A A A     A   AA  A                                   A                                       
             |                       A                                                                                              
             |         A A                  A    A                  A    A                                                          
        -0.1 +                                                    A                 A                                               
             |                                                     A                                                                
             |        A                                       AA                 A                                                  
             |                                                                                                                      
             |                                                              A                                                       
             |                                                                                                                      
        -0.2 +                       A                    A      A                                                                  
             |                                                                                                                      
             |                                                                                                                      
             |                                                                                                                      
             |                                                                 A                                                    
             |                                                                                                                      
        -0.3 +                                                                                                                      
             |                                                                                                                      
             ---+--------------+--------------+--------------+--------------+--------------+--------------+--------------+--        
              0.00           0.20           0.40           0.60           0.80           1.00           1.20           1.40         
                                                                                                                                    
                                                                  Flux1                                                             

here is my resid vs fitted plot, i was not sure it seems ok, could you help me? what should do next, if I face this type of plot.

---

[smorkoc]

Thanks for the help. I will consider transformations for the variables.

[PaigeMiller]

Is flux1 truly the fitted value (which can also be called the predicted value), or is it actually the X value used in the regression? 

[smorkoc]

It is fitted value (predicted value).