Looking over the comments, WOW, please please PLEASE read the paper! This title on HN is very misleading. A static type system had no POSITIVE effect on development time. The study is casting doubts on POSITIVE impact of static type systems.
To quote:
We measured two different points in the development: first, the development time until a minimal scanner has been implemented, and second the quality of the resulting software measured by the number of successful test cases fulfilled by the parser. In none of these measured points the use of a static type system turned out to have a successful impact. In the first case, the use of a statically typed programming language had a significant negative impact, in the latter one, no significant difference could be measured.
This study is way to small and limited to show much of anything... but many of the proponents and historical engineering studies that advocate static typing don't claim that it reduces "development time" so much as reduce the times/costs throughout the entire life cycle of the product. In fact, the "development time" or in this case "prototype time" hasn't been all that terribly interesting.
What would be interesting is to take these same projects, and same team members and add some features a year later and see what that looks like and then take the same project and give it to a new team after 6 months and have them add some minor feature or fix a bug and measure that. Or double the performance of the project and measure what that costs, if it's possible. etc.. It's fun to argue and advocate for what you like though.
To quote:
We measured two different points in the development: first, the development time until a minimal scanner has been implemented, and second the quality of the resulting software measured by the number of successful test cases fulfilled by the parser. In none of these measured points the use of a static type system turned out to have a successful impact. In the first case, the use of a statically typed programming language had a significant negative impact, in the latter one, no significant difference could be measured.