## 3 Results
### Package Characteristics  
The R packages in our review can be assigned to one of three categories:  
1. Packages that combine descriptive features with targeted DQ checks (Figure 5A);
2. Packages that focus on statistical overviews and on data exploration (Figure 5B);
3. Packages that perform highly focused checks based on an input of rules (Figure 5C). The first category comprises packages that combine a wide range of descriptive features with the possibility to perform targeted checks. They explicitly focus on DQA and are mostly suitable for users with limited programming skills. dataquieR, dataReporter, DQstats, MOQA, and pointblank belong to this category, with the latter being the most popular package (Figure 5A). pointblank offers two different types of reports: a descriptive report, which can be produced through a single function, and a report on DQ checks, which have to be defined by the user first. The latter approach is similar to the rule-checking packages (in category 3) and enables customized DQ reports creation. The reports generated by dataReporter can be compiled in different formats (R Markdown, PDF, HTML, and MS-Word) and, with additional programming, extended to include further checks and visualizations. dataquieR can automatically generate reports in the form of an interactive dashboard, but manual reports of varying scope may also be generated using R Markdown. For reporting, dataquieR uses a large set of helper functions to ensure its robustness with deficient study data and metadata. MOQA produces a separate PDF report for each variable, potentially resulting in many files. Only DQstats and dataquieR enable users to import metadata from a separate file (i.e., a CSV file with a specific structure). dataquieR and MOQA allow users to specify missing value codes. However, these implementations differ: in MOQA, only one general missing threshold for numerical variables and only one list of valid categories for categorical variables can be defined, while in dataquieR, these can be variable-specific. MOQA crashed if inadmissible categorical values exist in the data, but manual pre-processing can circumvent this issue. In this group, the packages pointblank and dataquieR cover the largest number of domains. Most packages belong to the second category (Figure 5B). Two of them offer a GUI: ExPanDaR and explore. The former exports reports as R Markdown Notebooks, while the latter generates HTML reports using R Markdown. The package dlookr offers two different types of reports with detailed information on DQ issues and exploratory data analysis, in the form of PDF or HTML files. In contrast, summarytools generates a brief but concise HTML report, which can be triggered by a single function. DataExplorer has a similar feature, but produces a more comprehensive report than summarytools, including  
Figure 4: General feature comparison across the 27 packages included in this review (Section 2.2.2). a wider range of figures, such as correlation heat maps. The package SmartEDA produces reports comparable to that of DataExplorer, but includes pairwise scatter plots instead of a correlation heat map and a more extensive data overview. The packages clickR, mStats, skim, StatMeasures, and xray mainly give a descriptive variable overview, but do not include stand-alone reports. The package visdat is similar in this regard, but follows a unique approach by providing mainly graphical output. While the package inspectdf equips each of its functions with a matching plot, it differs from visdat in providing the output also in a tabular format. Regarding additional functionalities for packages in the second category, inspectdf and visdat are able to compare two datasets, but inspectdf offers more functionalities in this regard. The largest collection of functions is provided by DesCTools, which includes descriptive data overviews, data cleaning, visualizations, and statistical tests. It has no function to generate a complete report automatically, but it offers functions to export R output to MS Word and PowerPoint.