## 4 Exploratory Data Analysis
\begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt}} \hline
**Data Description** & **Variables Relevant to the Main Description** \\ \hline Data characteristics & Age of participants is represented as a continuous variable. \\  & Gender: A categorical variable that is successively represented by the digits 0 and 1 for male and female. \\  & Pack history: A pack of twenty cigarettes that was smoked every day for a year is the continuous variable for the pack history. \\  & Smoking: The categorical variables for smoking and not smoking are represented by 1 and 2, respectively. \\ \hline Disease status & COPDSEVERITY is a categorical variable used to describe COPD severity at its advanced stages. GOLD from 1 to 4 are considered mild, moderate, severe, and the last GOLD is considered extremely severe, respectively. \\  & CAT: The data collection contains an unknown variable. \\ \hline Ability to walk & MWT1: Continuous variable to indicate the patient’s initial attempt at a measurement of the number of meters they cover in six minutes. \\  & MWT2: Continuous variable used to reflect the patient’s second attempt at measuring the number of meters covered in six minutes. \\  & MWT1 Best: The patient’s best effort to cover the distance in meters in six minutes is represented by the continuous variable MWT1 Best. \\ \hline Lung function & FEV1: A constant that represents lung function. It measures how much air, measured in liters, may be expelled from the lungs in one second. \\  & FEV1 PRED: Predicted FEV1 \\  & FVC: Constant is a measure of lung function that represents the maximum volume of air a person can exhale in a single breath, expressed in liters. \\  & FVCPRED: “FVC” prediction \\ \hline Mental health conditions & HAD: HAD categorical variable. For consecutively experiencing anxiety, depression, or neither, the scale accepts values between 0 and 1. \\ “Anxiety and Depression” & SGRQ: The quality-of-life index is represented by the continuous variable SGRQ. \\ \hline Quality of life & Higher life quality is associated with lower value. \\ \hline \end{tabular}
\end{table} 
Table 1: Variables for dataset. Figure 2 complements Table 2 by visually reinforcing the summary statistics, confirming the observed distribution, and emphasizing the age concentration around the mid-60s to mid-70s range. Table 3 summarizes the descriptive statistics for FEV1, a continuous variable representing the volume of air (in liters) that an individual can forcibly exhale in one second--a key indicator of lung function. The analysis revealed a mean FEV1 value of 1.6 L, with a SD of 0.67 L, suggesting moderate variability around the mean. The distribution of FEV1 values ranged from a minimum of 0.45 L to a maximum of 3.18 L. The 25 th percentile (Q1) was 1.1 L, the median (Q2) was 1.6 L, and the 75 th percentile (Q3) was 1.96 L, indicating a moderately right-skewed distribution with the bulk of observations concentrated between 1.1 and 1.96 L.  
The data showed 100% validity with no missing values, ensuring that the results are robust and reliable. The density plot illustrated in Figure 3 complements the statistical summary by visually depicting the distribution of FEV1 values. The smooth curve reflects the frequency of observations across the range of values, highlighting the central tendency and spread, while aligning closely with the calculated mean and quantile ranges. \begin{table}
\begin{tabular}{c c c} \hline Validity & 100\% \\ \hline Missing values & 0\% \\ \hline Mean & 70.1 \\ \hline Standard Deviation & 7.86 \\ \hline Quantiles & 44 & min \\ \hline  & 65 & 25\% \\ \hline  & 71 & 50\% \\ \hline  & 75 & 75\% \\ \hline  & 88 & max \\ \hline \end{tabular}
\end{table} 
Table 2: Age variable descriptive statistics. Figure 2: Density plot–age. Table 4 summarizes the statistical description of a sample of observations for a variable of interest. The sample had a mean value of 2.95 and a SD of 0.97.