My model fit indices as mentioned above for the sample size of 600 is more than 0.8 but not meeting the rule of thumb of more than 0.9 value can this value be considered and what are the ways to improve the model fit values
Values below .90 for CFI/TLI tend to indicate poor fit. There are general problems with all those indices. My view is that it is best to rely on the chi-square test of model fit and to look at covariance residuals and modification indices to examine sources of model misfit.
Model fit indices provide valuable information about how well your statistical model fits the observed data. While the rule of thumb suggests values above 0.90 for certain fit indices, the interpretation of fit indices should not be solely based on these cutoffs. The choice of fit indices and their acceptable values can depend on the complexity of the model, the nature of the data, and the research context.
Here are some key points to consider:
Complex Models: Complex models may naturally result in slightly lower fit indices. If your model includes many parameters or is testing intricate relationships, achieving very high fit indices might be challenging. In such cases, it's important to focus on the overall interpretability and theoretical soundness of the model.
Consider Multiple Indices: Instead of relying on a single fit index, consider looking at a combination of fit indices. Different fit indices measure different aspects of model fit, and the consensus among them can provide a more comprehensive understanding. Common fit indices include the Comparative Fit Index (CFI), Tucker-Lewis Index (TLI), Root Mean Square Error of Approximation (RMSEA), and Standardized Root Mean Square Residual (SRMR).
Incremental Improvement: Small variations in fit indices might not necessarily indicate a need for substantial model changes. Instead of striving for a perfect fit, aim for incremental improvements while maintaining theoretical justification.
Model Modifications: If your fit indices are significantly below the recommended thresholds and you believe your model has theoretical or practical merit, you can consider making targeted modifications to improve model fit. This might involve adding or removing paths, considering alternative variables, or investigating potential sources of misfit.
Local Misfit and Model Respecification: Fit indices can also provide insight into specific aspects of your model that might not fit well. Investigate modification indices and residual covariances to identify potential areas for model respecification.
Sample Size Consideration: Larger sample sizes can lead to more stringent fit index requirements. If your sample size is smaller, it might be more challenging to achieve very high fit indices.
Replication and Validation: If your model's theoretical framework is supported by existing research or established theories, this can enhance the validity of your model, even if fit indices are slightly below recommended thresholds.
It sounds like you are referring to fit indices used to assess the goodness-of-fit of a statistical model, often in the context of structural equation modeling (SEM) or similar techniques. Fit indices provide information about how well the proposed model fits the observed data. While there are recommended guidelines for fit index values, the decision of whether a value slightly below the threshold can be considered acceptable depends on the specific context and the overall research goals.
Typically, a fit index value greater than 0.90 is considered good, while values greater than 0.80 might be considered acceptable, especially if you have theoretical or practical justifications for why the model might not achieve a higher fit. The decision to accept or reject a model based on fit indices should be made in combination with other factors, such as theoretical reasoning, model complexity, and practical implications.
If your fit indices are not meeting the desired thresholds, here are some strategies to consider for improving model fit:
Simplify the Model: If the model is overly complex, consider removing or combining variables or paths that might not contribute significantly to the overall theoretical framework. Reducing complexity can improve fit.
Modify Model Specifications: Review your model's specifications. Are there logical or theoretical reasons for certain paths to be included or excluded? Make sure your model accurately reflects your theoretical framework.
Include Covariates: Adding relevant covariates that were not initially included in the model can help account for unexplained variance and improve fit.
Respecify Paths or Relationships: Re-evaluate the relationships between variables. Are there paths that should be added, removed, or changed based on theoretical reasoning or prior research?
Consider Measurement Model: If you're using latent variables, assess the measurement model (reflective and formative indicators). Poor measurement models can affect overall fit.
Modify Error Terms: Adjust the error terms based on theoretical considerations or the results of modification indices (if available in your software).
Check for Modification Indices: Many SEM software packages provide modification indices that suggest possible changes to improve model fit. Be cautious with this approach; while modification indices can be helpful, they shouldn't be followed blindly without theoretical justification.
Sample Size: If possible, increasing the sample size can lead to more stable parameter estimates and potentially improve model fit.
Consider Alternative Models: Sometimes the initial model you proposed might not be the best-fitting one. Consider testing alternative models and comparing their fit to see if there's a better representation of your data.
Use Multiple Fit Indices: Rely on multiple fit indices rather than just one, as some fit indices might be sensitive to specific issues in the model.
Remember that improving model fit should be guided by theoretical reasoning and prior research. While achieving high fit indices is desirable, the ultimate goal is to have a model that accurately represents the theoretical framework and provides meaningful insights into the relationships among variables.
Thank you for this question. I often had this problem. I am learning enormously from the comments already made on this question. Following these, I can modestly say that the Model fit indices examine the fit between the model and the data. CFI and TLI indices below 0.95 indicate a mismatch between the model and the data. The analysis of the modification indices indicates the source of the problem and makes it possible to correct the model (as stated by those who commented before me). Similarly, adjustment problems can be related to theoretical relationships between model elements. I could be wrong, but I think that a model or a modeling must be based on theoretically valid relations before being tested statistically. Some problems with model fitting would arise from the fact that the model variables are not logically related. this is a basic theoretical problem that can adversely affect model fit by showing poor fit indices. See Hu and Bentler (1999) for model fit criteria.