## 4 Results and Discussion
### Level 1: Descriptive Statistics  
The general purpose of this Level 1 is to observe 4973 light-duty vehicles from 2017 to 2021 by their fuel consumption and carbon dioxide emissions from different brands, vehicle models, vehicle class, cylinders, engine size, transmission, fuel type, smog rating, and fuel consumption in a city and on a highway. Recall that the CO\({}_{2}\) and smog ratings in the dataset were calculated using manufacturer ratings rather than vehicle testing, and were ranked from worst (1) to best (10) with no unit. Firstly, in order to address RQ1.1 (How do light-duty vehicles compare in terms of fuel consumption and carbon dioxide emission? ), descriptive statistics for all numerical columns in the dataset have been conducted to provide an evaluation of the data distribution. The purpose of descriptive statistics is to provide a statistical understanding of the dataset quality [36]. It can be seen from Table 1 that the average total fuel consumption is 10.86 L/100 km, of which 57.77% (12.36 L/100 km) from the city and 42.22% from the highway (9.04 L/100 km). Additionally, it is clear from the statistics that the average CO\({}_{2}\) emissions of all vehicles are 251.44 g/km, with a standard deviation of 58.85 g/km. Ranking from worst (1) to best (10), the average CO\({}_{2}\) rating is 4.60, and the average smog rating is 4.63. Moreover, dispersion statistics of standard deviation and variance also indicate that the size of the distribution of values expected is reliable enough for prediction. Regarding the fuel consumption and carbon dioxide emission of different brands, their average data are indicated in Table 2.  
In this dataset, the number of vehicles from Ford accounts for the highest with 436 vehicles, and the lowest amount is from Bugatti with 6 vehicles. After the descriptive statistical analysis, a bar chart is created, as presented in Figure 2, to demonstrate the average fuel consumption of different brands. It reveals that Honda consumes fuel the least (8.03 L/100 km), while Bugatti has the highest fuel consumption (22.98 L/100 km). Moreover, from Figures 3 and 4, Honda seems to be the greenest brand as it emits the least CO\({}_{2}\) (187.58 g/km) and attains the highest CO\({}_{2}\) rating (6.65), whereas Bugatti continues to perform poorly in its environmental-friendliness with the highest CO\({}_{2}\) emissions (538.83 g/km) and the worst CO\({}_{2}\) rating (1.00). Considering smog, Figure 5 proves that Volkswagen emits smog the least (6.45), and Bugatti seems to be the worst brand in terms of smog (1.00), fuel consumption, and CO\({}_{2}\) emissions. Figure 3: CO\({}_{2}\) emissions (g/km) of each brand. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Brand** & **Engine Size (l)** & **Cylinders** & **Total Fuel Consumption (L/100 km)** & **CO\({}_{2}\) Emissions (g/km)** & **CO\({}_{2}\) Rating** & **Song Rating** \\ \hline Honda & 2.01 & 4.35 & 8.03 & 187.58 & 6.65 & 4. Regarding fuel consumption and CO\({}_{2}\) emissions of different models, Table 3 explains that the IONIQ BLUE model consumes and emits the least, and in contrast, the CHIRON PUR SPORT model consumes and emits the most. Similarly, when considering fuel consumption and CO\({}_{2}\) emissions, Tables 4-8 showcase that Station wagon (Small) class, Engine Size 1.2L, 3 Cylinders, Transmission Type AV1, and Fuel Type D (Diesel) consume fuel and emit CO\({}_{2}\) the least. Conversely, Van (Passenger) class, Engine Size 8.0, 16 Cylinders, Transmission Type A6, and Fuel Type E (Ethanol E85) seem to be the most consumers and emitters. However, since the Volkswagen emissions scandal emerged, the negative image of diesel has intensified. The actual NO and PM emissions of diesel vehicles, according to recent researchers, are significantly greater than those reported. Because of carcinogenic compounds, diesel particle emissions are also a possible health danger [38]. Therefore, the conclusion that Ethanol E85 emits the most among other fuel types remains the scope of the data in this research.