The phrase "ascertain how and when" is correct and usable in written English.
You can use it when you want to determine the specifics of a situation, particularly regarding timing and method.
Example: "We need to ascertain how and when the project will be completed to meet our deadlines."
Alternatives: "determine the timing and method" or "find out how and when".
But in the case of the Katrina debacle, the people have a clear interest in ascertaining how and why the administration failed in its response.
Although ascertaining how and exactly when this has happened is difficult, it seems most likely that the virus entered the country in December 2014, as evidenced by unverified accounts of increased poultry deaths in some live bird markets in Lagos, after the birds had been moved from the north (Kano) to the south during the festive season.
Watch how and when the person touches.
Learn how and when to interrupt.
To accommodate that gap, this study used content analysis and sequential analysis to ascertain how learner interaction differed when participants had access to success- and failure-based case libraries.
Ascertaining how, when and how often consumers use healthcare services is critical to effective healthcare policy and funding.
The face, content, and construct validity of the measures developed for nursing homes are relatively rarely points of debate, though a great deal of effort has been expended to ascertain how valid specific measures are when compared to direct observations of care [ 14- 17].
There, over a couple of beers, marketers can run through the available ad space in, say, a newspaper, and ascertain how much an advertiser is willing to pay.
Experts are trying to ascertain how far the underground cavity reaches and whether more homes are at risk.
More work needs to be done to ascertain how best teaching can be developed to develop skills and knowledge, and how this translates into clinical practice.
