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Step 4. Validating ANOVA Assumptions
As stated in Example #1, there are three assumptions in ANOVA analysis: normality, constant
variance, and independence. The normality plot of the residuals is used to check the normality of the
treatment data. If the distribution of residuals is normal, the plot will resemble a straight line. The
constant variance assumption is checked by the plot of residuals versus fitted values. If the plot of residual
vs. fitted values (treatment) does not show any pattern, the constant variance assumption is satisfied. If
the plot of residual vs. run order (time order of data collection) does not reveal any pattern, the
independence assumption is satisfied. It seems that there is nothing unusual about the residuals in
Example #2.
P value
None of the P values was below 0.05.
Thus, we cannot reject the null
hypothesis, which is the lead-free solder
joint shear strength of 0402 is same at
different reflow profile.

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