How dry is the sky?

Measurements over Western Europe (by British investigators) indicate a uniformly dry lower stratosphere, with frost points around −82°C and mixing ratios of about 2 milligrams/kilogram, while other observations over North America imply frost points from −60° to −85°C, with mixing ratios varying up to several hundred milligrams/kilogram. Since no theory is able to explain all the observations, they must be re-examined for possible bias or error.