Tham khảo tài liệu 'engineering statistics handbook episode 5 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | . How can I test whether or not the random errors are distributed normally Important One important detail to note about the normal probability plot and the histogram is that they Note provide information on the distribution of the random errors from the process only if 1. the functional part of the model is correctly specified 2. the standard deviation is constant across the data 3. there is no drift in the process and 4. the random errors are independent from one run to the next. If the other residual plots indicate problems with the model the normal probability plot and histogram will not be easily interpretable. NIST SEMATECH HOME I TOOLS AIDS search BACK NEXT http div898 handbook pmd section4 7 of 7 5 1 2006 10 22 15 AM . How can I test whether any significant terms are missing or misspecified in the functional part of the model Testing Model Adequacy Requires Replicate Measurements The need for a model-independent estimate of the random variation means that replicate measurements made under identical experimental conditions are required to carry out a lack-of-fit test. If no replicate measurements are available then there will not be any baseline estimate of the random process variation to compare with the results from the model. This is the main reason that the use of replication is emphasized in experimental design. Data Used to Fit Model Can Be Partitioned to Compute Lack-of-Fit Statistic Although it might seem like two sets of data would be needed to carry out the lack-of-fit test using the strategy described above one set of data to fit the model and compute the residual standard deviation and the other to compute the model-independent estimate of the random variation that is usually not necessary. In most regression applications the same data used to fit the model can also be used to carry out the lack-of-fit test as long as the necessary replicate measurements are available. In these cases the lack-of-fit .
