Hi every one!
Do you know that what is this error in General Linear Model in Minitab 18?
''The following terms cannot be estimated and were removed: A*B''
Why some times Minitab can't calculate some interactions of parameters?
And how can I fix this problem?
because I need to calculate the P-value of interaction of this parameter!
Interaction effects occur when the effect of one variable depends on the value of another variable. Interaction effects are common in regression analysis , ANOVA, and designed experiments. In this post, I explain interaction effects, how to interpret them in statistical designs, and the problems you will face if you don’t include them in your model.
In any study, whether it’s a taste test or a manufacturing process, many variables can affect the outcome. Changing these variables can affect the outcome directly. For instance, changing the food condiment in a taste test can affect the overall enjoyment. In this manner, analysts use models to assess the relationship between each independent variable and the
dependent variable . This kind of an effect is called a main effect. However, it can be a mistake to assess only main effects.
In more complex study areas, the independent variables might interact with each other. Interaction effects indicate that a third variable influences the relationship between an independent and dependent variable. This type of effect makes the model more complex, but if the real world behaves this way, it is critical to incorporate it in your model. For example, the relationship between condiments and enjoyment probably depends on the types of food .Example of Interaction Effects with Categorical Independent Variables
I think of interaction effects as an “it depends” effect. You’ll see why! Let’s start with an intuitive example to help you understand these effects conceptually.
Imagine that we are conducting a taste test to determine which food condiment produces the highest enjoyment. We’ll perform a two-way ANOVA where our dependent variable is Enjoyment. Our two independent variables are both categorical variables : Food and Condiment.
Our ANOVA model with the interaction term is:
Satisfaction = Food Condiment Food*Condiment
To keep things simple, we’ll include only two foods (ice cream and hot dogs) and two condiments (chocolate sauce and mustard) in our analysis.
Another possible problem is sample size. Since you are doing a factorial experiment your model requires that the experiment must be replicated to have enough data to estimate all of your parameters. For full details see:
https://www.amazon.com/Design-Analysis-Experiments-Douglas-Montgomery/dp/1119589061/ref=sr_1_1?keywords=Montgomery+Design+of+Experiments&qid=1565029798&s=books&sr=1-1
Good luck, David Boot
It is most probably because you do not have replicas of your experimental data. Sometimes, in order to have the interaction effects of your factors on your response, you need to have multiple responses for each combination of your factors by repeating the experiments for each combination.
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