SQT Blog

Some experimenters believe that you must always include centre points when designing experiments. This is not the case, and in particular, it doesn’t make sense to include centre points when designing screening-type experiments, with large number of factors.

Centre points have an important role in testing for curvature in the appropriate circumstances, but will not provide an aid in the search for factors with significant main and/or interaction effects , which is the main objective when screening.

Centre points can be added to the design, if desired, when we have completed our screening work, and we are contemplating proceeding to optimisation using Response Surface Methodology (RSM).

I sometimes see people including a single centre point when designing screening experiments. This makes no sense. A single centre point is completely useless and is simply a wasted experimental run.

There is a view among some experimenters that adding centre points gives you a three-level design. This is not the case. Centre points are located at the centre of the design space and have no role in determining effects of the factors at the middle value of the factor levels.

Learn more about the correct use of centre points by attending our Design of Experiments courses. We present two Design of Experiments courses; a three day Design of Experiments on both a public and in-house basis and a six day Design of Experiments for R&D on an in-house basis.

Lean Tutor required with experience in the Manufacturing Sector. Lean experience in the Services sector and a qualification as a Lean Six Sigma Black Belt would be advantageous.

Please contact Éamon O’Bearra on 087 267 0480 or email eamonobearra@asst.ie

Some experimenters are of the view that it is always necessary to replicate designs in order to test for significant effects. As a consequence, some experimenters will replicate fractional factorial designs. This doesn’t make sense.

Consider the case of a quarter fraction, 2-level design of 6 factors in 16 runs. There is considerable aliasing among the two factor interactions, about which we will be concerned. See the alias structure here reproduced from Minitab:

Alias Structure

I + ABCE + ADEF + BCDF

A + BCE + DEF + ABCDF
B + ACE + CDF + ABDEF
C + ABE + BDF + ACDEF
D + AEF + BCF + ABCDE
E + ABC + ADF + BCDEF
F + ADE + BCD + ABCEF
AB + CE + ACDF + BDEF
AC + BE + ABDF + CDEF
AD + EF + ABCF + BCDE
AE + BC + DF + ABCDEF
AF + DE + ABCD + BCEF
BD + CF + ABEF + ACDE
BF + CD + ABDE + ACEF
ABD + ACF + BEF + CDE
ABF + ACD + BDE + CEF

Replicating this design will require 32 runs, but the additional 16 runs won’t assist in breaking up the aliases among the two factor interactions. After the replication we will have a more powerful test for significance of effects, but we will continue to have the same degree of aliasing as before the replication. Instead, if there are resources available for 32 runs, it makes much more sense to use the 32 runs to design a half fraction, in which, in this particular case, there won’t be aliasing among the two factor interactions. The power to test for significant effects will be much the same as that achieved from the replicate on the quarter fraction, because the additional insignificant effects that are likely to be produced using a half fractions can be converted to sums of squares, and will perform much the same role as the replicate on the quarter fraction. That is; you will have much the same ability to detect significant effects, while avoiding aliasing among the two factor interactions, for the same 32 experimental runs.

Learn more about the correct use of fractional designs by attending our Design of Experiments courses. The next public Design of Experiments course is a three day course scheduled for 5th – 7th June in Dublin. This course can also be run on an in-house basis. We also have a six day Design of Experiments for R&D course. The latter is run as an in-house course.

As allergen control is identified as one of the 10 fundamental clauses of the BRC Global Food Safety standard, FBOs, (Food Business Operators), need to have a structured approach to managing allergens within their operation.

A practical way of ensuring that your allergen management programme is fit for purpose is to ensure compliance with the 10 point allergen improvement plan.

1 Allergen policy As allergens are 1 of the 4 food safety hazards, companies need to develop an allergen policy to demonstrate their commitment to legal compliance.

2 Risk Assessment As all contempoary Food Safety standards are based on risk assessment, each manufacturing process step needs to be risk assessed for the potential of allergen x contamination.

3 Supplier Management As a significance number of allergen x contamination incidents occur off site at supplier locations, suppliers must be risk assessed for the potential of allergen x contamination.

4 Recipe/Spec Control All manufacturing recipes and other product specs need to address allergen content to ensure that required information is shared between businesses in the food chain.

5 Labeling Review All finished product labels must be validated prior to use to ensure that they comply with all relevant Labellling legislation, ref Commission Directive 2007/68/EC annex 111A.

6 Operational Control All risk assessment evaluations undertaken by the food safety team must be transferred to factory floor manufacturing operations to ensure the relevant knowledge is in place.

7 Cleaning Validation All cleaning operations which historically focussed on the elimination of microbiological, biological and chemical hazards need to be re-validated to ensure the same procedures are capable of eliminating allergenic hazards.

8 Employee Training All staff, via induction training or specific on-the-job training, need to be made aware of the allergen risks in the manufacturing environment.

9 Change Control/Change-Over When allergenic and non-allergenic materials are processed on the same manufacturing equipment, change over procedures need to be formalised to ensure x contamination does not occur and the correct label is applied to the new manufacturing product.

10 Consumer Data FBOs, in an effort to demonstrate due diligence, need to investigate all possible means, (product labeliing, product websites), to inform consumers of the risks associated with products being produced.

If this 10 point allergen improvement plan is followed by food businesses, they can demonstrate that they are taking a structured and logical approach to allergen management.

Our next public Food Allergen Control training course takes place on 23rd April in Dublin