Professional Detailing2 min read

Blocking a Coating Trial by Operator or Day: Make Comparisons Fairer

Use operator or day blocks to reduce confounding in a coating trial and preserve the block structure when analysing results.

Updated · NANOLAB Knowledge

Blocking groups experimental work so that known background differences can be accounted for. If operator or day is likely to influence a coating trial, comparing every product within each relevant block can be more informative than assigning one product to one operator and another to someone else.

Avoid a confounded comparison

Suppose an illustrative trial has two products and two operators. If operator A applies only product 1 and operator B only product 2, a difference may reflect the operator, product or both. Having each operator apply both products under a planned design separates those questions more effectively.

Within each block, randomize the order where appropriate and maintain the defined preparation and measurement process. Blocking does not mean giving a preferred product the easiest panel every time.

Choose blocks for a reason

Useful blocks might include application day, substrate batch or operator, depending on the question. Too many poorly planned categories can make a small study difficult to interpret. Decide which background differences matter before collecting the outcomes.

Keep block identity in the dataset. Averaging it away before analysis loses the benefit of the design. An appropriate statistical method should reflect the block structure and independent experimental units.

Report the scope clearly

A result consistent across the tested operators is stronger for that workflow than a result obtained by one specialist alone. It still does not prove that every installer will achieve the same outcome. Training and adherence to the product instructions remain relevant.

For a NANOLAB evaluation, blocking can make a modest trial more informative without turning it into a much larger project. The goal is to reduce avoidable ambiguity about whether a difference comes from the product or from the circumstances in which it was applied.

Related guidance

Technical references: NIST: Randomized block designs.

For product-specific application instructions, consult NANOLAB technical documentation or ask about your surface and intended use.