The phrase "a key factor when" is correct and usable in written English.
It can be used to introduce an important element or consideration in a specific context or situation.
Example: "A key factor when evaluating the success of a marketing campaign is the engagement rate of the target audience."
Alternatives: "an essential element when" or "a crucial aspect when".
"Good parks improve property values," he said, "and people consider parks a key factor when they evaluate the livability of a neighborhood".
For Detective Chief Superintendent John Coles, who heads Operation Trident, a specialist Metropolitan Police unit which targets black-on-black gun crime, a key factor when women or children are shot is the killers' ethnicity.
The city's ability to carry out this plan in a timely manner will be a key factor when the federal Environmental Protection Agency decides in 2002 whether to continue to allow the city to avoid filtration.
The reversal magnetic responsivity of DTH-Fe3O4@SiO2 would be a key factor when evaluating their recoverability [61].
The thermal expansion coefficient of porcelain body is a key factor when considering the thermal match between body and glaze.
The reliability of the optical constants is a key factor when analyzing the validity of the numerical model.
I guess to some extent that probably speaks to you having enough content and a nice way of presenting...I think that's a very key factor when it comes to working on who are the people that take the message out.
Their main function is to increase the stability of NPs in a solution, which is the key factor when considering the suitability of the capping agent for the nanosuspension preparation [15, 16].
The vanishingly small impact of the investigated demographic and socioeconomic factors indicates that the travel costs in terms of time and money is the key factor when a patient decides whether to contact the out-of-hours service or not.
Organization is the key factor when starting a new business.
Due to the presence of multiple redox couples at the reference electrode inserted into the VRFB membrane, the adjustment of the current flowing through the DHE with the resistor is the key factor when attempting to maintain a stable and steady hydrogen reduction reaction at the DHE during repeated charge and discharge processes.
