LCL (Lower Control Limit)

The Lower Control Limit (LCL) is a threshold in statistical process control charts, typically set a fixed number of standard deviations below the process mean. When a process measurement falls below the LCL, it indicates that the process may be out of control on the lower side.
See also: UCL (Upper Control Limit), Control Charts

LTPD (Lot Tolerance Percent Defective)

LTPD stands for Lot Tolerance Percent Defective. It represents the worst acceptable quality level for a lot in acceptance sampling. The LTPD defines the percentage of defective items in a lot that is tolerable with a specified confidence level, helping to decide whether to accept or reject a lot.
See also: Acceptance Sampling, Quality Control

LSS (Lean Six Sigma)

LSS stands for Lean Six Sigma and refers to a methodology that integrates Lean principles (focusing on waste reduction) with Six Sigma techniques (focusing on reducing variability and defects). This approach aims to streamline processes and enhance quality and efficiency throughout an organization.
See also: Lean, Six Sigma

Lack of fit

Lack of fit is a term used in statistical modeling and experimental design to describe the degree to which a proposed model fails to capture the underlying trend of the data. When a model exhibits significant lack of fit, it means that the systematic variations in the data are not adequately explained by the model.
See also: Model Adequacy, Residual Analysis

Latin square design

A Latin square design is an experimental design that arranges treatments in a square grid so that each treatment appears exactly once in each row and once in each column. This design is effective at controlling for two extraneous sources of variability (e.g., time periods, locations) simultaneously.
See also: Experimental Design, Randomized Block Design

Lead time

Lead time is the total elapsed time from the initiation of a process to its completion. In manufacturing and supply chain management, it typically refers to the time from receiving a customer order to delivering the final product, including production and transit times.
See also: Cycle Time, Throughput Time

Lean

Lean is a management philosophy and toolset that focuses on creating maximum value for customers by reducing waste and optimizing processes. By eliminating non-value-added activities, lean systems aim to improve efficiency, quality, and customer satisfaction.
See also: Kaizen, Continuous Improvement

Lean Six Sigma

Lean Six Sigma is a comprehensive process improvement methodology that combines the waste-reducing principles of lean manufacturing with the defect-reducing focus of Six Sigma. It employs structured problem-solving frameworks such as DMAIC (Define, Measure, Analyze, Improve, Control) to drive measurable improvements in quality and efficiency.
See also: LSS, Process Improvement

Least squares method

The least squares method is a statistical approach used to determine the best-fitting line or curve for a set of observations. It works by minimizing the sum of the squared differences (errors) between observed values and the values predicted by the model, making it a cornerstone technique in regression analysis.
See also: Regression Analysis, Curve Fitting

Levene’s test

Levene’s test is a statistical procedure used to assess the equality of variances across different groups. This test is particularly useful as a preliminary step before conducting analyses like ANOVA, where the assumption of equal variances is crucial.
See also: Homogeneity of Variance, ANOVA Assumptions

Lower control limit (LCL)

Refer to the definition for LCL (Lower Control Limit) above.

Lower specification limit (LSL)

The Lower Specification Limit (LSL) is the minimum acceptable value for a product characteristic or process variable as defined by design or quality standards. Measurements below the LSL indicate nonconformance to required specifications, potentially leading to product rejection or the need for rework.
See also: Upper Specification Limit (USL), Tolerance Limits