Maximizing Data Accuracy: A Machine Learning Engineer's Guide to Data Cleaning 

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Maximizing Data Accuracy: A Machine Learning Engineer's Guide to Data Cleaning 

Data Cleaning in Machine Engineering: what is it, again? 

Building reliable, high-performance Machine Learning (ML) systems often require access to large amounts of high-quality data. Nevertheless, in practice, data is seldom clean because of noise introduced by human data curation or the unavoidable defects introduced by automation data collection. Examples of such problems include the prevalence of inconsistent or missing data in real-world datasets due to malfunctioning sensors or human error, which may impact the performance of machine learning systems.

When the reliability of the data it contains decreases, the time and effort invested by the end-users in ensuring its correctness slow down the process. When the quantity of dirty records increases, the flaws caused by adding manual procedures become more obvious. Building any machine learning application almost always starts with the cleansing of the underlying data. 

Data cleaning may be broken down into two distinct categories: traditional data cleaning and data cleansing for large data. It is because of this inability to manage massive amounts of data that conventional data-cleaning techniques are considered "traditional." 

Data accuracy: what is it, and why machine-learning engineers should care? 

Data accuracy: definition and examples

There is no consensus on what constitutes data accuracy. The most widely accepted definitions focus on the correctness, precision, and error-free nature of the data or the degree to which an estimated value corresponds to the real value. Hence,  data accuracy is evaluated by considering various metrics, such as the validity of the data, the presence of errors, and the precision of the data. 

Using these metrics, you may assess how reliable the data is. Data accuracy refers to how faithfully and correctly a database represents the facts and figures that matter to a certain field of study or industry. To evaluate the data's accuracy, consider the following factors: 

  • The data must match up with the real world.

  • We must not afford to have some flaws in the data.

  • For the data to live up to the standards set by the users, it has to be very comprehensive.

  • The data must be well-detailed, according to the needs of the project at hand.

Why should ML engineers care about it? 

Let's take a look at some statistics to establish a baseline before discussing why ML engineers should care about Data accuracy:

According to Gartner: “Poor data quality destroys business value. Recent Gartner research has found that organizations believe poor data quality to be responsible for an average of $15 million per year in losses.”

Pragmaticworks mentioned that “77% of companies believe they lost revenue because of inaccurate/incomplete contact data.”

Data accuracy is among the data quality dimensions. It is essential to minimize the analysis-stage uncertainty caused by missing information. If there are errors or missing numbers in the data, the analysis will turn out differently, negatively impacting the business choice. Achieving success depends on having reliable data to stay out of the red and save money. Due to the potential for contamination among the numerous data sources, data accuracy is essential for producing reliable results.


Examples of data labeling errors

In the competition among corporations to be the first to use AI solutions and revolutionize their business procedures, data labeling seems to be the stumbling block that holds everyone back. You will get high-quality results from well-labeled data and poor results from poorly-labeled data. Data annotation is a significant challenge for companies using AI technologies. Hence, let's examine the common errors made while labeling data.

Missing label

A missing label error might occur if the annotator fails to draw a bounding box around every required object in the image. If the annotator isn't paying close enough attention or is in a rush, they may overlook important information. This kind of mistake, along with all others, should be avoided at all costs, as fixing them usually requires starting the data-labeling process over again. It is possible to prevent this mistake by using proper techniques of communication. The supervisor can adopt a review procedure in which the annotators must have their work reviewed to ensure its quality.

Improperly Fit

In this case, the box isn't accurately portraying the object and will produce inaccurate data, which may hurt the result. To avoid wasting time, the supervisor can have many people annotate the same collection of images to reach an agreement (or consensus) on the optimal annotation for each image. Only the annotations that get unanimous approval will be used to train the model.

Annotator Bias

When there are an overwhelming number of annotators who all share the same perspective, this leads to models that are tainted with bias. Our Article Things that Can go Wrong During Annotation and How to Avoid Them provides us with the following example:

“There are less insidious forms of annotator bias, too. If you’re working with annotators who speak British English, they’ll call a bag of potato chips “Crisps.” Your American English speakers will label the same data “Chips.” Meanwhile, your British English speakers will reserve the “Chips” label for fries. That inconsistency will reflect in the algorithm itself, which will arbitrarily mix American and British English into its predictions.” 

To prevent this from happening, it is advised that an annotator has a thorough understanding of the data being labeled. The supervisor can provide guidance on the data type that is most appropriate for the target model and the data type that is less beneficial.

Adding new tags

A potential source of concern for annotators is the discovery, midway in the process, that more tags were needed in the label but had been neglected. This situation can create trouble. To prevent this mistake, supervisors should spend their time compiling a comprehensive list of labels; ideally, they would also have expertise in the relevant area; failing that, they should seek out the assistance of a specialist.

Countless listings of tags

If you have many tags to choose from, it will be much more difficult for your annotator to achieve their job, ultimately leading to a worse quality outcome. You can prevent this by organizing your tags according to their broadest possible themes.

Failure to use appropriate data labeling tools

From the inception of AI, data has expanded dramatically in volume and complexity. If you're working using outdated tools, it's likely that the scope of the job has grown beyond the resources at hand. Poorly collaborative software might be to blame if your annotators are having trouble communicating or forgetting to complete tasks.
Verifying Data Accuracy and Completeness

Validating Data Accuracy

Data quality is ensured by a procedure called "data validation," which involves checking incoming information against a set of criteria that has already been established. From basic checks to more complex checks, there is a wide variety of methods available for guaranteeing data accuracy.

By checking for errors, data validation guarantees reliable results. Failure to use validated data might cause programs to crash, provide erroneous results, or cause other serious problems.

Checks are used in almost every kind of data validation. These tests, which are often executed in chronological order, do nothing more than "test" the validity of the data. When data has been checked and validated, it is either sent on to the next step or stored in a database. 


Ensuring Data Completeness

When evaluating the data quality in a database, completeness is a key metric. The term refers to how well a system captures and stores information pertinent to a certain application domain. This implies that the system should have a complete and accurate representation of all external facts.

There are two components to completeness:

  • The first one is to consider whether a given entity class contains all mandatory entities. This implies that the system contains every component required for a given class.

  • The second factor is checking for the presence of non-empty data values for mandatory attributes. This means that all the necessary attributes of a particular entity should be present in the system and should not be empty.

One facet is referred to as "entity completeness," while the other is "attribute completeness."

Incomplete data might cause discrepancies and mistakes that lower the quality and trustworthiness of the results. For example, to properly target individuals, you need more than a name. Leads that expressed enthusiasm for your company but whose information is missing represent lost opportunities for further communication. Because of this, many possibilities go unexplored due to a lack of information.

Correcting Data Errors and Missing Information

Fixing Data Errors: Structured Data

Learning what causes errors is the first step. Understanding the underlying causes of this recurring issue and the accumulation of useless data in your database is essential before taking any corrective action. If you know the typical causes of erroneous data, you have a higher chance of resolving the problem.

Automation and standardization of the data-gathering process can greatly impact if human error is the main problem in data. The next step is to plan and stick to a regular update cycle for your infrastructure. An orchestration platform can assist those who lack the requisite technical expertise to construct such automated data operations. 

Fixing Data Errors: Review and issue management using the Kili Technology Platform

The occurrence of a missing label can be avoided with the use of well-established channels of communication. The supervisor has the option of initiating a review process in which the annotators are required to submit their work for review. Kili Technology provides two perspectives from which to review assets:

In both circumstances, you can review labeled assets using a review interface that's quite similar to the labeling interface. After that, you can:

Kili Technology's automatic workload distribution mechanism streamlines load management, shortens the time it takes to annotate projects, and eliminates the possibility of errors caused by unnecessary repetition. If multiple users are working together on an annotation project, the Kili Technology application will distribute the data to be annotated so that each annotator works with their unique set of data. Except when using Consensus, data won't be annotated twice.

Reviewers can submit issues as a means of communicating with those responsible for labeling. Both the “issue button” and the Analytics page display the current count of open issues.

When using the Kili Technology platform, It is possible to add issues while reviewing labeled assets:

Note 1: There are two ways to start a new project in Kili: via the GUI and through programming.

Note 2: Using the project Queue page, you can switch to the Explore view. In the Explore view, you can perform the following:

The Transition from Hands-On asset inspection to automatic error detection

Maintaining high-quality data is a major challenge in building an accurate model. Suppose you have to assign labels to a dataset of tens of thousands of documents, but you don't have access to any automated review tools or a way to automatically protect your labeling guidelines while receiving real-time feedback on your work. Kili users in large numbers sometimes run bespoke code in parallel to increase throughput and quality while labeling. Kili Technology's engineers have added a new dimension to their labeling solution by allowing users to integrate third-party plugins into the labeling process.

This increased modularity will strengthen and streamline your labeling procedure. Each time an object is tagged with a plugin, any mistakes will be immediately highlighted. Several applications might be conceived of:

  • If you want to identify just single cells and not groups of cells in a video, you can adjust the bounding box's maximum size using a plugin.

  • The ability to set a lower and upper limit on the number of vertebrae to be labeled in medical imaging.

And there might be much more! If you're interested in trying it, here's a resource to help you to learn the basics.

Completing missing data

There are a number of potential causes for missing data, including errors made during data input or collection. To cope with missing data, you may either remove the partial information or substitute an estimate for the missing value based on the remaining data. This process is called imputation. 

Choosing the most appropriate technique for a specific dataset depends on the data type, the amount of missing data, and the purpose of the analysis. Analysis outcomes may be affected by the method used. For example, mean imputation may be more appropriate for continuous data, while mode imputation may be more appropriate for categorical data. 

The imputation method that is used depends on the cause of the missing data; thus, pinpointing that cause is critical. There might be three possible explanations for why a value is missing:

  • It was lost or never recorded;

  • It doesn't apply to this particular case; 

  • it's irrelevant to this particular instance.

Suppose we are in a medical environment. The variable may be assessed, but for some unknown reason, the data is not stored electronically because: 

  • The sensors may have been disconnected, there could have been a communication fault with the database server, a worker could have overlooked something, or the electricity could have gone out. 

  • There is no need to assess this variable since it has no bearing on the patient's state and would be of little clinical use to the doctor.

As an example, forward fill allows us to infer values based on their predecessor, like in the below example where the data is collected in chronological order:


Transforming Data for Better Results

Normalizing Data for Consistency

The degree to which a data collection satisfies certain integrity criteria is referred to as the level of consistency in that data set. When it comes to protecting the reliability and authenticity of your data, "integrity constraints" are the ground principles you must adhere to. A value in a given field may only be between 2 and 20, depending on the nature of the restriction. Information in that field is deemed inconsistent if it does not conform to the aforementioned specification.

A company's internal teams can only work effectively together if they can access consistent data. If data is normalized, consistency can be maintained amongst departments like R&D, marketing, and sales. Data that is consistent from one department to the next will streamline processes and make it easier to compare data. 

Converting data into the right format

Data conversion refers to the process of shifting data from one data type to another.  The purpose of data conversion is to safeguard the information contained inside and its underlying structures from being damaged or lost in the process. If the target format has the same capabilities and data structures as the original data, the conversion process will be straightforward.

Reducing Data for Better Efficiency

Removing Duplicate Data Points

Data analysis is an integral aspect of the decision-making process in modern businesses. Cleaning it up first is essential before drawing conclusions. 

One crucial step in cleaning data is getting rid of duplicates. At the very least, storing several copies of the same information slows down processing. The worst-case scenario is that duplicate information compromises the reliability of the dataset, skewing the findings of any analyses performed.

Eliminating Irrelevant Data

Machine learning is a branch of AI that allows computers to infer meaning from data, spot patterns, and act autonomously without being explicitly programmed. Data is analyzed by algorithms to draw conclusions and generalize new data. Healthcare, banking, retail, and other sectors use machine learning. Machine learning's predictive abilities and data-driven insights have made it a game-changer for firms wanting to stay ahead of the competition. 

Predicting the future based on data that has not yet been gathered or seen is a common use case for decision-making systems. If the System is trained with poor data, it will make incorrect decisions.

If we want our prediction models to function well, we must exclude irrelevant data from the training process. Improving performance involves reducing the time required to build the model and decreasing the total number of features through feature selection.

Open-Source Solutions for Cleaning Machine Engineering Data


The main objective of ydata-profiling is to provide a consistent and quick solution for online EDA (Exploratory Data Analysis). data-profiling, much like the useful pandas df.describe the () function, provides a thorough examination of a data frame and lets you export the results in several formats, including HTML and JSON. ydata-profiling saves us from having to visualize the distribution of each variable manually. A complete report is generated and made accessible to you with just a click.


Errors in the input data reduce the quality of the resulting models, and this, in turn, leads to erroneous inferences about the models' efficiency.

Cleanlab inspects your ML data for errant labels and repairs them automatically. This aids in training trustworthy ML models on noisy real-world datasets by reducing the amount of human labor required to correct data inaccuracies.

If you're interested in image classification, check out our article on automatic error detection using Kili Technology and Cleanlab.

Great Expectations

When deciding to develop an analytics strategy or build a machine learning model, it is crucial first to verify the accuracy of the data being used. There should be an up-front awareness of and documentation of any redundancies in data. Data quality issues are common throughout the ETL design process, but data validation and quality checks can be performed using Great Expectations, and the results can be documented and displayed in an attractive, straightforward user interface.


With refinery, you can quickly build labeled training data and test out new ideas with little effort. refinery goes much beyond its labeling capabilities. The greatest benefits come from the automation and data management features, albeit it does include a labeling editor built in. It's helpful for both data analysis and labeling management. You will be able to save time and effort while improving the quality of your models through the automation of countless repetitive tasks, gaining a deeper understanding of the data labeling workflow, and receiving documentation for your training data.


Data Cleaning: Best Practices for Machine Engineering Data

Backing Up Data Before Cleaning

It is crucial for cleaning businesses to have a data backup strategy in place so that, should a catastrophe occur, operations can be resumed with minimum downtime. Even though there are cheap data storage alternatives available today, many businesses still lack a backup strategy. If the methods for backing up your data fail, having a backup plan B will increase your odds of a successful recovery.

It is important to find out what kind of backup procedures your company currently has in place and establish such a procedure if there isn't already one. You must:

  • Provide the location of the data copies: If you don't want to lose everything, store backups somewhere other than the original storage site.

  • Determine the files' accessibility (How to get into them)

  • Include details on any data-transfer restrictions or potential changes to the file format.

  • Set a minimum frequency for data backups.

  • Make it very clear who is accountable for making backups.

  • Set up an automated system for backups: Although it's possible to back up individual files manually, doing so on a regular basis and without missing any is much easier with an automated approach.

  • Inspect backup: When a backup is complete, it's important to double-check the files to ensure they open without a hitch.

  • Determine the backup's retention period.

Documenting the Data Cleaning Process

It is critical to document your data-cleaning operations so that you can monitor any changes made to the data. Your hard work will be useful for future data analysis studies if you document it thoroughly. For your document, you may think about:

  • Various forms of noise in the data

  • Strategies for removing useless details

  • Note any data that must be excluded because of background noise.

Verifying Cleaned Data for Accuracy

Accuracy checks rely heavily on starting with clean data. Therefore, that should be your first priority. Whether it's bad information or just too much of it, data cleansing may get rid of it. A single corrupt record in your database may ruin the bunch. Working with low-quality data may be more detrimental than helpful. So it's worth it to filter out the data that isn't useful to your organization.

Implementing a Regular Data Cleaning Schedule

How frequently you should perform a  "data cleaning" is something that should be tailored to the specific demands of your company.

A major company can amass a mountain of data, requiring periodic data cleaning. Data cleansing should be performed at least annually, especially for smaller firms with less data. Nonetheless, a data cleanse should be scheduled if there is any concern that filthy data is lowering profits or reducing efficiency.

The Importance of Data Cleaning for Machine Engineers

Data Cleaning Techniques: Summary

The best possible insights and outcomes can be achieved with proper data, increasing productivity. It is imperative that we take the following actions to clean up our data:

  • Validate Data Accuracy;

  • Ensure Data Completeness;

  • Fix Data Errors;

  • Normalize Data for Consistency;

  • Convert Data into the Right Format;

  • Remove Duplicate Data Points;

  • Eliminate Irrelevant Data.

The Critical Role of Data Cleaning in Machine Engineering

Errors and irregularities in the training data might hinder pattern detection by algorithms. Hence it is critical to clean the data before using it. This procedure requires many rounds to achieve a steady state where the data has been cleaned up to the point that it faithfully represents the real distribution without any biases. 

Data Cleaning for Machine Learning Engineers: Final Thoughts

Lack of data cleaning can result in squandered time and money, a decline in efficiency, and a failure to capitalize on marketing opportunities. AI-powered tools can help identify patterns in large datasets, identify anomalies in the data, and suggest corrections or modifications improve accuracy.


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