Just-in-time (JIT) manufacturing is among the most commonly researched topics in the area of operations management. In a recently published paper, my co-author and I examine the relationship between JIT manufacturing practices and performance outcomes by means of meta-analysis of correlations approach. Based on an in-depth analysis of literature spanning from 1992 to 2008, the results of this meta-analytic investigation support a positive relationship between JIT manufacturing practices and aggregate performance. However, the findings suggest that not all individual JIT practices are associated with all types of performance outcomes. This study highlights the JIT practices that have the greatest impact on individual performance outcomes and emphasizes the role of moderating factors in the relationship between JIT practices and performance. The following JIT practices and performance measures were considered for this research investigation:
JIT PRACTICES:
Setup time reduction: Extent to which the plant is reducing setup times in production;
Small lot sizes: Extent to which the plant is utilizing or working towards using small lots in production;
JIT delivery from suppliers: Extent to which the plant is receiving shipments from vendors on a JIT basis;
Daily schedule adherence: Extent to which the plant is producing to schedule as well as utilizing time buffers to guard against unexpected stoppages in production;
Preventive maintenance: Extent of proper maintenance of machinery such that the production machinery downtime is limited;
Equipment layout: Extent of use of cellular manufacturing design including close proximity of machinery;
Kanban: Extent to which operations in the plant utilize the concept of kanban;
JIT link with customers: Extent to which the plant provides JIT deliveries to customers;
Pull system: Extent of existence of a pull production system and the related supporting systems;
Repetitive nature of master schedule: Extent of consistency of production scheduling, as well as the variation in product volumes.
PERFORMANCE:
Quality performance (e.g. scrap rate, rework rate);
Manufacturing cost (e.g. unit cost);
Inventory (e.g. inventory turns, inventory levels), cycle time (e.g. manufacturing cycle time, lead time, and throughput time);
Manufacturing flexibility (e.g. mix, modification, volume, new product, and expansion) and delivery performance (e.g. delivery reliability, delivery speed).
The significant positive association between aggregate JIT and aggregate performance constructs is not surprising given both the widespread adoption of JIT in practice as well as the general support of this relationship found in extant literature. Analyzing the relationship between individual JIT practices and aggregate performance yields several interesting insights. First, all JIT practices are positively associated with aggregate performance. This indicates that each JIT practice results in improved aggregate performance even though the practice may not be positively associated with performance measures, when considered individually. For instance, kanban is significantly associated with aggregate performance but at the individual performance level it is associated with only three performance metrics (i.e. inventory, flexibility and delivery performance). Second, the results indicate that while most of the associations between individual JIT practices and aggregate performance are generalizable (not subject to moderating factors) across contexts, the association of small lot sizes, pull system and preventive maintenance with aggregate performance are subject to moderating factors. This implies that although these three relationships are significant and positive, the context in which these practices are used could influence magnitude of the achieved aggregate performance improvements.
An analysis of the relationships among individual JIT practices and performance outcomes suggest that about one-fourth of the JIT practice to performance relationships are not significant. This outcome indicates that when evaluating JIT practices for their potential impact on various performance outcomes, firms should not assume that all JIT practices improve all aspects of performance. Furthermore, almost half of the relationships among JIT practices and individual performance outcomes are subject to moderating factors suggesting that firms should be cautious in forming performance expectations and tailor JIT implementations by taking the underlying context into consideration. The moderating effects could be manifested in the form of indirect associations of JIT practices with some performance measures. For instance, although small lot sizes were not found to be significantly associated with cycle time performance, it is possible that reduced work in process inventories and organized work environment fostered by small lot sizes may lead to improved cycle time. The level to which this potential indirect association may manifest in certain situations could influence the magnitude of the direct impact of small lot sizes on cycle time performance. Additionally, JIT practices may interact with each other resulting in varying degrees of improved performance. In cases where JIT practices are likely implemented together, such as when equipment layout and pull systems are implemented with other JIT practices, such as small lot sizes and setup time reduction, potential interactions among these practices could influence the magnitude of performance outcomes.
Along with the indirect and interaction effects of various JIT practices, in several organizations some of the impact of JIT practices may be redundant in the presence of other infrastructural practices. This could result in a lack of evidence for significant associations of these practices with various performance outcomes. For example, management support may act as a surrogate for kanban. This could explain the lack of association between kanban and cycle time performance. Potential redundancies also exist between kanban and JIT scheduling systems such that one could replace the other in improving quality performance.
Given the widespread adoption of the various JIT practices in business settings, the managerial implications of this metaanalysis could be far reaching. This meta-analytic investigation enables identification of those JIT practices that positively influence various performance outcomes. This understanding provides a starting point whereby existing and future JIT practice to performance relationships may be evaluated. To aid in this type of evaluation, the study highlights the ‘‘breadth’’ and ‘‘depth’’ of impact for each JIT practice. A JIT practice has a high breadth impact when multiple performance outcomes are significantly improved. The depth impact of individual JIT practices is captured in terms of the magnitude (average correlation) of the significant relationships between individual JIT practices and performance outcomes. In a resource constrained context, as is the case in most real business situations, managers can evaluate their implementation options based on the overall impact (breadth and depth) of a JIT practice on performance. In this regard, the impact factors can act as a guide for the implementation of those practices that will yield the greatest impact.
Our study also informs practice by showing that there could be a wide range in possible performance benefits associated with implementing many of the JIT practices. The performance benefits of several of the significant relationships between JIT practices and performance outcomes are influenced by other unknown factors. Thus, managers implementing JIT practices should be cognizant that the approach for JIT implementation and the environment in which JIT practices are implemented and utilized could impact the effectiveness of the JIT practices in improving performance. It is likely that firms implementing the same JIT practices may see widely varying effectiveness of these practices and therefore mimicking and benchmarking activities, without adequate attention to the context, may turn out to be ineffective in gaining the desired performance outcome.
Source: Mackelprang, A. and Nair, A. 2010. Relationship between Just-in-Time Manufacturing Practices and Performance: A Meta-Analytic Investigation. Journal of Operations Management, 28, 283-302.