Background
Performance or outcome variables of process, product depend up on many parameters and their variability. These independent X variables would have impact on output Y variables. For example;
Fuel efficiency of an automobile depend on – Quality of Fuel (V1), Speed of Vehicle ( V2), Maintenance of Vehicle ( V3) etc
Output quality and yield of batch in chemical / pharmaceutical manufacturing impacted by - Temperature, pressure in reaction, quality, purity of input raw materials etc.
During design or process development stage – many experiments are conducted in R&D laboratories or pilot labs to understand impact each variable (Factors) on the outputs at different input range (levels). As long as these experiments are less cost intensive, less time consuming with less resource utilization, multiple tests with combination of factors and levels can be done easily. However when cost , time, resources involved in such experiments are significant, then it is extremely important that few experiments are conducted to see results as per experiment protocol. The criticality of such experiments would go up exponentially wrt to cost / time/ resources/ outcomes, when conducted at scale-up level from 1L in laboratory to 1 KL at plant scale. A statistical method that is used in selecting such impact-full experiments is known as “Design Of Experiments”.
Design of experiments – play very important role in pharmaceutical manufacturing process especially in active pharma ingredients (API ), oral solid dosage forms ( OSD) . In API synthesis manufacturing process, Temperature, pressure of key reactions and purity of input play important role in outcome of API with respect to yield, purity. For 2 different ranges of ( levels) of these factors , there would be 8 combination of experiments that can be conducted as per below formula.
No. of Experiments = (Levels)Factors
Conducting such number of experiments at Plant scale is very difficult as cost, time, resources used are very high. In actual manufacturing process, these type of variables (factors) affecting output variables / quality run into 10s. In such scenarios, a random way of conducting experiments are just not acceptable. Even design of experiments has be done with proper back ground work.
Following would help in improving Design of Experiments and their outcome.
Understanding interactions with in Xn and between Xn and Yn. Conduct as many gram scale laboratory experiments as possible to understand all interactions of factors
·Gain process knowledge as much as possible with these multiple experiments. In some cases especially for safety evaluations “what-if” experiments are done to understand extreme conditions, deviations. Runways
Arrive at Critical Process parameters / factors affecting the output ( may 80-20 rule, pareto analysis, Risk Priority number etc)
Define nuisance random variables which can be blocked that can mitigate interference in experiment outcomes ( fraction factorials).
Take guidance from subject matter experts within or outside industry to gain best in process knowledge
Conclusion
All above (but not limited to) , one can arrive at fractional factorial design of experiments and same can be conducted with higher probability of success rate with minimal impact on resources. That is the reason one says “Good planning is Half the job done” and same specially true in case of Design of experiments.