| Value | Category | 
                                    
                    
                        | 1 | electricity | 
                                    
                    
                        | 2 | gas | 
                                    
                    
                        | 3 | paraffin | 
                                    
                    
                        | 4 | wood | 
                                    
                    
                        | 5 | coal | 
                                    
                    
                        | 6 | candles | 
                                    
                    
                        | 7 | animal dung | 
                                    
                    
                        | 8 | solar energy | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.