A Pareto diagram is the most appropriate tool for this task. It is a specialized bar chart that displays the frequency of different categories of problems (in this case, defect types) in descending order. A cumulative frequency line is often included. This format is specifically designed to highlight the most significant factors in a dataset, applying the Pareto principle (the "80/20 rule"). It allows Sheela to clearly and effectively report on the most commonly occurring product defects, thereby helping stakeholders prioritize which defect types to address first for the greatest impact.

A. A cause and effect diagram (or Ishikawa diagram) is used to explore and display the potential causes of a specific effect or problem, not to rank different defect types by frequency.

B. A scatter plot is used to visualize the relationship or correlation between two continuous numerical variables, which is unsuitable for categorical data like defect types.

C. A histogram is used to represent the frequency distribution of a single continuous variable, not discrete categories like "coding errors" or "requirements errors."

1. Pressman, R. S., & Maxim, B. R. (2020). Software Engineering: A Practitioner's Approach (9th ed.). McGraw-Hill. In Chapter 17, "Software Quality Assurance," Section 17.3.2 discusses statistical SQA and the application of Pareto analysis to identify the "vital few" defect causes that lead to the majority of errors (p. 469).

2. Naik, K., & Tripathy, P. (2008). Software Testing and Quality Assurance: Theory and Practice. Wiley. Chapter 16, "Software Quality," describes the seven basic quality tools. Section 16.4.1 specifically details the Pareto chart as a tool for prioritizing problems by arranging them in decreasing order of importance, often based on defect counts (pp. 458-459).

3. Ahmed, A. A. E., Abd El-Gawad, I. A., & El-Wahab, A. A. A. (2016). A proposed approach for analyzing software defects using Pareto principle. 2016 IEEE 7th Annual Information Technology, Electronics and Mobile Communication Conference (IEMCON), 1-6. This paper explicitly states, "Pareto chart is one of the most powerful quality tools. It is a graphical tool to map and rank business process problems from the most recurrent to the least frequent." (Section III.A). https://doi.org/10.1109/IEMCON.2016.7746331