Data Cleaning: What It Is, Why It Matters & How to Do It

What is Data Cleaning?

Data cleaning, sometimes referred to as data cleansing or scrubbing, involves revising, rectifying, and organizing information in a dataset to make it consistent and ready for analysis. This step entails identifying and addressing errors, inconsistencies, duplicates, or incomplete entries within the data. The main objective of data cleaning is to enhance the data's quality and usefulness, thereby leading to more dependable and precise findings.

Ensuring optimal performance in data analysis involves the crucial step of refining and optimizing datasets. This includes addressing and amending incorrect, inconsistent, improperly formatted, redundant, or incomplete entries within the data. The primary goal of data cleaning is to improve the quality and usability of the data, which ultimately leads to more accurate and reliable insights.

How Is Data Cleaning Different from Data Transformation?

Separately from data cleaning, data transformation is the process of converting data from one format or structure into another. This process is a fundamental aspect of data integration and data management tasks, such as data wrangling, data warehousing, and application integration. Data transformation can involve various techniques, such as normalization, attribute construction, and filtering. The goal is to make the data more accessible and easier to handle. Where data transformation deals with the changing of types and structure of data, data cleaning is focused on taking data and ensuring its accuracy and reliability are of a high enough standard for businesses to rely on.

Why Is Cleaning Data Important?

Cleaning data is vital for organizations seeking to foster a culture focused on quality and data-driven decision making. This process of data cleaning involves rectifying or eliminating incorrect, flawed, improperly formatted, duplicated, or incomplete information within a dataset. This ensures that the conclusions and analyses drawn from the data remain consistent and precise. When data from various sources are merged, it opens up numerous chances for duplication or mislabeling of data, resulting in outcomes and algorithms that might be unreliable, even if they seem correct on the surface. By ensuring uniformity within a single dataset or among several datasets, data cleaning assists organizations in steering clear of the "garbage in, garbage out" dilemma.

Data cleansing also plays an integral role in the overall data management strategy and is a crucial part of the data preparation phase, setting the stage for datasets to be used in business intelligence (BI) and data science endeavors. Through pinpointing data inaccuracies and modifying, refreshing, or deleting data to rectify them, data cleansing enhances data quality, delivering more precise, coherent, and trustworthy information for organizational decision making. This procedure is commonly performed by data quality experts, engineers, or other data management specialists—although data scientists, BI analysts, and business users may also engage in data cleansing tailored to their particular applications.

What Kind of Data Errors Does Data Cleaning Fix? 

Data cleaning addresses a wide range of errors in datasets, ensuring that the data is accurate, reliable, and suitable for analysis and decision making. Some common data errors often found while cleaning data include:

• Duplicate records: These occur when the same data entry is mistakenly repeated in a dataset, leading to redundancy and potential inaccuracies in analysis.
  
  
• Inaccurate data: This refers to data entries that contain incorrect values, such as typographical errors, wrong numerical entries, or syntax errors. Inaccurate data can lead to misleading or erroneous insights and conclusions.
  
  
• Missing or incomplete data: This occurs when certain data fields are left blank or contain null values, which can affect the overall quality and reliability of the dataset. Missing or incomplete data can result in biased or incomplete analysis and decision making.
  
  
• Inconsistent data: Inconsistencies can arise when data is formatted differently across various sources or systems, leading to discrepancies in values, units, or terminology. Inconsistent data can make it difficult to accurately analyze and interpret the information, potentially causing confusion and misinterpretation.

By identifying and addressing these common data errors, data cleaning ensures that the dataset is of high quality and suitable for use in various applications, such as business intelligence, analytics, and decision making.

Characteristics of Quality Data

Quality data is essential for making informed decisions and driving business success. To ensure that data is of high quality, it should meet five key characteristics. When cleaning data before using it for analysis or decision making, consider the following aspects:

• Validity: Valid data adheres to the rules and constraints set for the specific data type or field. Ensuring validity means checking that the data falls within the acceptable range of values and follows the correct format.
  
  
• Accuracy: Accurate data is free from errors and closely represents the true value. To ensure accuracy, data cleaning should involve identifying and correcting any incorrect or misleading information.
  
  
• Completeness: Complete data contains all the necessary information and does not have any missing or null values. Data cleaning should involve filling in missing values or addressing incomplete records to ensure a comprehensive dataset.
  
  
• Consistency: Consistent data maintains the same format, units, and terminology across the dataset. Data cleaning should involve identifying and resolving any discrepancies or inconsistencies to ensure uniformity and comparability.
  
  
• Uniformity: Uniform data follows a standard format, making it easier to analyze and compare. Data cleaning should involve converting data into a common format or structure, ensuring that it is consistent and easy to work with.
  

By addressing these five characteristics during the data cleaning process, you can ensure that your dataset is of high quality and suitable for use in various applications, such as business intelligence, analytics, and decision making.

How to Clean Data

By following a systematic approach to cleaning data, professionals in analytics, data engineering, and data science can eliminate errors, inconsistencies, and inaccuracies, ultimately leading to better decision making and more valuable insights.

For this section, we will use the example of an online e-commerce and retail store looking to clean its data to actively get better insights from its analytics tool.

1. Identify data discrepancies using data observability tools

Before diving into the data cleaning process, it is crucial to identify the discrepancies that must be addressed. Data observability tools can help you monitor your data for inconsistencies, errors, and anomalies. These tools can provide valuable insights into the health of your data, allowing you to prioritize areas that require cleaning. 

For instance, if you are working with a dataset containing customer information and notice inconsistencies in the "email" field, data observability tools can help you quickly identify these issues and determine their extent. Imagine your dataset comprises customer information for an online retail store. The system may reveal that some customers have provided phone numbers instead of email addresses in the "email" field. By focusing your data cleaning efforts on resolving this specific problem, you ensure that your dataset is accurate and reliable for further analysis.

2. Remove unnecessary values

Datasets may sometimes contain irrelevant or redundant information that is unnecessary for your analysis. In such cases, it is essential to identify and remove any records or fields that do not contribute to the insights you are trying to derive. For example, the online retail store dataset might have a "preferred store location" column for physical pickups. However, if your analysis solely focuses on online purchases, this column becomes irrelevant and can be removed. By eliminating unnecessary values, you can streamline your dataset, making it more manageable and focused on the relevant data points, thus leading to more accurate and reliable insights.

3. Remove duplicate data

Duplicate data can skew your results and lead to inaccurate insights. It is essential to identify and remove any repeated records in your dataset. For instance, a customer might have accidentally submitted their information twice in the online retail store dataset. This duplication could lead to an overestimation in customer counts. Eliminating duplicate data ensures your analysis is based on unique and accurate information, leading to more reliable insights and better decision making.

4. Fix structural errors

Structural errors refer to issues with the layout and format of your data, such as inconsistencies in units, date formats, or misaligned fields. Correcting these errors is crucial to ensure your data is consistently structured and easily interpretable. For example, in the online retail store dataset, you may find that some dates are in the format MM/DD/YYYY while others are in DD/MM/YYYY. Standardizing these date formats ensures consistency and prevents errors during analysis. Additionally, you may need to align mislabeled fields, such as correcting a customer's ZIP code that has been mistakenly entered in a phone number field.

5. Address any missing values

You need to include values to ensure the results of your analysis. To address this issue, you may fill them using interpolation or regression techniques or remove records with missing values altogether. For example, if the dataset from the online retail store has absent values in the "purchase amount" field, you might use regression techniques to estimate what these values might have been based on other data points. Handling missing values effectively ensures that your dataset is as complete and accurate as possible, leading to more reliable insights.

6. Standardize data entry and formatting

To ensure consistency in your dataset, enforce standards for how data is entered and formatted. This might involve creating conventions for naming, units of measure, or categorization. For example, you could standardize the format in which names are entered in the retail dataset, such as always using a title case. By standardizing data entry and formatting, you can minimize errors and inconsistencies, making your dataset more reliable and easier to analyze.

7. Validate and correct values against a known list of entities

Ensuring that your data adheres to expected values or formats is crucial for maintaining data integrity and accuracy. One way to achieve this is by cross-checking your data against a predefined list or dataset. For instance, in the online retail store dataset, you can cross-check the ZIP codes against a known list of valid ZIP codes to ensure accuracy. By validating and correcting values against a known list of entities, you can identify and rectify any discrepancies or inconsistencies in your dataset. This process helps to maintain the quality and reliability of your data, ultimately leading to more accurate insights and better decision making for analytics users, data engineers, analytics engineers, and data scientists.

Data Cleaning Best Practices

To maintain a clean and healthy database, consider implementing the following best practices:

Develop a data quality strategy

Developing a data quality strategy is essential for aligning data cleaning efforts with overall business objectives. A well-defined strategy ensures that data management processes are in line with the organization's goals, leading to more accurate analysis and informed decision making. By focusing on data quality, organizations can maintain a clean and reliable database that supports their business needs effectively.

Correct data at the point of entry

Ensuring data is entered correctly at the point of entry is a crucial aspect of maintaining a clean and reliable database. By focusing on accuracy and attention to detail during the initial data entry process, organizations can save valuable time and resources that would otherwise be spent on cleaning and correcting errors later on. Implementing data entry best practices  can help minimize the risk of errors and improve overall data quality. Those best practices include: establishing accuracy goals and standards, using validation tools, and staying up-to-date with the latest technology. By prioritizing correct data entry from the start, businesses can maintain a more efficient and accurate database that supports their objectives and decision making processes.

To ensure accuracy in data entry, consider implementing the following best practices:

• Establish goals and standards for data entry: Set accuracy goals and standards based on your business expectations and the type of data entry project.
  
  
• Leverage labels and descriptors: Organize data collection by sorting it into different fields or categories, ensuring that it is complete and well-formatted based on your needs.
  
  
• Detect errors early: Implement validation tools and processes to identify and correct errors in the early stages of data entry.
  
  
• Make use of automation in data entry: Utilize data entry software and tools to minimize the risk of human error and improve overall data quality.
  
  
• Double key entry verification: Implement a double key entry verification process. That’s where two individuals independently enter the same data and any discrepancies are flagged for review and correction.

Validate the accuracy of your data

Consistent validation checks play a crucial role in maintaining data integrity within an organization. By regularly verifying the accuracy of your data, you can identify and correct errors, inconsistencies, and discrepancies that may have been introduced during the data entry process or through system updates. Implementing validation checks, such as data validation rules, data profiling, and data quality audits, can help ensure that your data remains accurate and reliable over time.

To ensure the accuracy of your data, it is essential to implement various data validation techniques. Some best practices for data validation include:

• Use a combination of validation techniques: Employ both client-side and server-side validation methods to improve the accuracy and security of the data validation process.
  
  
• Perform data type and format checks: Verify that the data entered has the correct data type and follows the predefined format, such as date columns being stored in a fixed format like "YYYY-MM-DD" or "DD-MM-YYYY."
  
  
• Implement field-specific and cross-field checks: Conduct field-specific checks, such as checking for the presence and uniqueness of fields, formatting, and numerical bounds, as well as cross-field checks to ensure the consistency of values within a given time snapshot where there are dependencies.
  
  
• Use data validation tools: Utilize tools with self-validating sensors for effective data analysis and validation checks. Employ multiple tools for better results and consistency.
  
  
• Double-check for outliers: Identify and rectify any outliers in your data to maintain its accuracy and consistency.

Create a Data Entry Standards Document (DES) and share it across the organization

Creating a Data Entry Standards Document (DES) and sharing it across your organization is an essential step in ensuring uniformity and accuracy in data entry processes. A DES serves as a guideline for how data should be entered and maintained, providing clear instructions and expectations for employees involved in data entry tasks. By establishing and adhering to a well-defined set of data entry standards, your organization can minimize errors, improve data quality, and maintain a consistent and reliable database.

To create an effective DES, consider including the following elements:

• Data entry goals and standards: Define accuracy goals and standards based on your organization's expectations and the type of data entry project.
  
  
• Formatting and data type requirements: Specify the required formats and data types for each field or category, ensuring consistency across the organization.
  
  
• Validation and error detection: Outline the validation tools and processes to be used for identifying and correcting errors during data entry.
  
  
• Automation and technology: Encourage the use of data entry software and tools to minimize the risk of human error and improve overall data quality.
  
  
• Training and documentation: Provide training and resources for employees to ensure they understand and adhere to the established data entry standards.

Regularly audit and monitor data quality

Periodic audits and monitoring of data quality are essential for maintaining a clean and reliable database. Regular audits help identify new issues and evaluate the effectiveness of the data-cleaning process. By consistently assessing the quality of your data, you can detect errors, inconsistencies, and discrepancies, allowing you to address them promptly and maintain the integrity of your database.

To effectively audit and monitor data quality, consider the following steps:

• Establish data quality metrics: Define clear metrics for measuring data quality, such as the number of incomplete or redundant entries or the amount of data that cannot be analyzed due to formatting incompatibilities.
  
  
• Perform data quality assessments: Conduct regular assessments of your data using various techniques, such as data profiling, data validation rules, and data quality audits.
  
  
• Track changes over time: Monitor the progress of your data quality improvement efforts by comparing the results before and after data cleaning and identifying trends and patterns in data quality issues.
  
  
• Implement data quality monitoring tools: Utilize tools and software to automate the monitoring process and detect errors in data more efficiently.
  
  
• Evaluate the impact of data cleaning: Perform a cost-benefit analysis to determine if the effort and cost associated with data cleaning are worthwhile. Compare the potential gains in data quality, model performance, and decision-making capabilities against the resources invested.
  

Data Cleaning Tools & Software

There are several data cleaning tools and software available that can help streamline the process of cleaning and preparing data for analysis. Here are some popular options:

• Sigma AI - Input Tables: Sigma's AI product, Input Tables, can clean, classify, extract, and autofill table data effortlessly. This tool is particularly useful for those already using Sigma's platform for data analysis.
  
  
• OpenRefine: Formerly known as Google Refine, OpenRefine is a powerful open-source tool for working with messy data. It allows users to clean, transform, and extend data with web services and external data sources.
  
  
• WinPure: WinPure is an affordable data cleaning tool that can handle large datasets, remove duplicates, as well as correct and standardize data. It supports various data sources, including databases, spreadsheets, and CRMs.
  
  
• Melissa Clean Suite: Melissa Clean Suite is a data cleaning solution that enhances data quality in CRM and ERP platforms like Oracle CRM, Salesforce, Oracle ERP, and Microsoft Dynamics CRM. It offers features such as data deduplication, data verification, contact autocompletion, data enrichment, and real-time and batch processing.
  
  
• Trifacta Wrangler: Trifacta Wrangler is a data cleaning tool that helps users explore, clean, and prepare data for analysis. It offers features like data profiling, transformation, and validation, making it easier to work with messy data.

These tools can help you maintain high-quality data, ensuring that your datasets are suitable for use in various applications, such as business intelligence, analytics, and decision making.

The Value of Data Cleaning

In conclusion, data cleaning is a vital process that enables organizations to maintain a high-quality database, which is essential for accurate analysis and decision making. By implementing data cleaning best practices and regularly auditing and monitoring data quality, businesses can ensure that their data remains accurate, reliable, and valuable for their needs. Investing in data cleaning not only helps organizations avoid the negative consequences of dirty data, but also unlocks the potential for improved productivity, customer acquisition, and overall business success.