DOE augmentation help with an already blocked design

[#1]

Hi there,

I was hoping I could get some help with an experiment I am currently running?

It is a custom design with 3 factors in total. 2 continuous variables and 1, 2-level categorical variable. This is ran on JMP 15.2

Lets call them

Continuous factor 1 = A (Range 25-75), Continuous factor 2 =B (Range 10-180) and Categorical factor= C( Acid, Neutral)

I was interested in collecting information in the middle of the range of the continuous variables as well as any 2nd order interactions so the model contains the main effects, 2nd order interactions and the quadratic terms for the continuous variables.

The default design suggested a 18 run design which was too many runs for one day so I selected to group the design into two blocks of 9 runs.

Block 1 of testing has now been completed and it is clear from eyeballing the data that Factor A appears to be the most important factor by far and that optimal results are only going to be found around the midpoint of this factor.  Block two of testing will proceed as planned but I am already thinking of how best to fix Factor A to its midpoint while seeing what impact varying factor B and C will have.

Would it be possible to augment the design while locking Factor A to its mid point or would this be difficult as the design already contains a blocking factor and augmentation would add a third blocking factor to the mix?

[#2]

Hi @Students_Tea,

Welcome in the Community !

When creating a design using blocking like you did, you group experimental runs into blocks that are similar to each other. The repartition of factors levels should be similar between blocks 1 and 2, so if you can't run experiments of block 2, the situation is similar to using a fraction of the full design. Using only half of the experiments planned in this situation will however results in :

•  High reduction of power to detect significant main effects and higher order effects:
  
• Higher prediction variance :
  
• Higher uncertainty for parameters estimates :
  
• Increase correlations between effects :
  

So you may already have detected a significant effect for factor A, both statistically and with a large effect size, but since you're degrading the ability to detect effects (and particularly higher order effects in which you seem to be interested) when using only the first block of your complete design, I would recommend running the other planned experiments from block 2 to better estimate effect from factor A and give you the ability to detect other effects (main effects and higher order effects).

You could also augment the design and changing the ranges of the factors : if A has a predominant effect on your response, you could augment your initial set of experiments from block 1 and restrict the levels/range of A to narrower values centered around the intermediate level (if you had good results in this area). This could help reduce the relative importance of factor A on the response. You could also expand ranges from factor 2, if it makes sense, to enable an easier detection of an effect.

I wouldn't fix a factor at this stage, you have a limited number of factors to study and very low power to detect effect when using only a fraction of your complete design. Fixing a factor so early in the experimentation stages could prevent you from detecting possible interaction between A and B, as well as a more precise estimation of possible quadratic effect of A and its main effect. Maybe the detection of interactions and quadratic effects (not yet detected at this stage) could lead you to a better optimum and a better overview and understanding of your system.

I attached a design similar to the one you seem to have so that you can reproduce the design comparison (full and subset with block 1 only) with the Compare Designs platform.

Hope this answer may help you,

[#3]

Hi @Victor_G 

Thanks very much for the follow up. I may have been a little unclear with how I plan to follow up the work from today.

My intention is to run Block 2 of the experiment as originally planned as I realise that it would mess up the design and the ability to glean information from the work performed so far if I did not do that.

"You could also augment the design and changing the ranges of the factors : if A has a predominant effect on your response, you could augment your initial set of experiments from block 1 and restrict the levels/range of A to narrower values centered around the intermediate level (if you had good results in this area). This could help reduce the relative importance of factor A on the response. You could also expand ranges from factor 2, if it makes sense, to enable an easier detection of an effect."

I think what you wrote above seems like the right idea. Expanding ranges for factor 2 doesn't really work in this case as the limits are essentially up against a practical wall so while we could make them wider any value derived beyond those limits just isn't practically useful.

I imagine it must be possible to Augment the experiment once the Block 1 and Block 2 parts are done but my knowledge of DOE's is not great. When I go to use the Augment Design (As a test) the existing Blocking factor in the design comes in as a choice. Should the existing blocking factor be included as an X-factor? When I do that, restrict the value of Factor A around the intermediate value and then then group new runs into a separate Block I end up with a design that's now 26 runs long in total and contains three separate random blocks and 2 Blocks. It appears its blocked the first two blocks into 1 block and then the augmented runs into a second block. It also doesn't contain any additional center points for A which I'm not sure if that's an issue. I do suspect the optimal values is at the midpoint of A so it would be nice to get some additional data at that point but maybe the design doesn't need it?

Please see attached for the design that comes up when I augmented the existing design as described above.

[#4]

Hi @Students_Tea,

Thanks for the clarification and sorry for my misunderstanding.

If you try to include your Random Block in the panel of the factors in the Augment Designs platform, then the random block factor will be removed in the next window :

 In your situation, what you could do is enter your factors A, B and C in the Augment Designs platform, modify the levels (if needed) for factor A, and check the option "Group new runs into separate block".

With the same assumed model (main effects, 2-factors interactions and quadratic effects), the number of added runs recommended by JMP would be 8, so you can increase this number to 9 (to match the number of runs in previous random blocks from the original design), and you'll get this design (note that I changed min level of factor A to 40 and max level to 60):

As you say, you will have three random blocks, and two blocks.

You could proceed with the analysis by using the 3 random blocks to check that the experimental variance in your experiments remains stable/constant (using a random effect through a Mixed model to assess its statistical significance). If you detect a statistical significance, check the effect size and where is the significant difference between the random blocks.

Hope this answer may help you, 

[#5]

Hi @Victor_G,

Thanks for you previous response. It's very helpful. The second day of data has just come in from the other half of the original design.

At first glance it appears that Factor A indeed has the biggest effect size looking at the response and so I was thinking of augmenting the design like you mentioned with a narrower range around Factor A. It appears that the quadratic effect of A (if I'm getting that right) is the biggest effect by far and this is obvious in the profiler from essentially a large curve with the minima in the center of the curve. One concern I have is that the raw data in its current form may not be great for telling me about Factors B and C.

For example it should be the case that at around the midpoint of Factor A, an increase in Factor B will result in the response lowering. The response can be a positive integer including zero but never less than zero. This is actually shown in the data but due to the large absolute values involved with the lowest and highest ranges of Factor A I think this is somewhat masked. When using the profiler for example and maximizing the desirability, Factor B is set to the lowest value 10, even though we know its capable of giving lower responses at the highest number 180.

I think another reason could be that the data is heteroscedastic? Part of me is wondering if it would be better to do some sort of transformation on the raw data (log or square root) to equalize out some of that variance so that the model can more easily distinguish the magnitude of the other factors? Does this sound like a good idea based on the data or does JMP correct for this?

Please see attached for the data table and Fit model parameters that are recommended.