McLaren had a control group, Edmonton, in this study. Having two very similar Canadian cities one having ceased fluoridation, one having not, presented a unique opportunity to assess the impact of cessation, against a control group which accounted for the various factors which normally inhibit such studies. Both Edmonton and Calgary showed increased dental decay rates between 2004 and 2014, however Calgary showed a statistically greater increase than did Edmonton. Given the similarity of the two cities, variables involved with dental decay incidence were sufficiently neutralized (controlled), leaving cessation of fluoridation in Calgary being the major difference between the dental aspects of the two populations. While McLaren clearly states in her study that it would have been preferable to have had baseline data closer to the 2011 cessation in Calgary, she took the only acceptable data available, that from a 2004-2005 survey, which utilized the same sensitive parameters as the ending data from the survey in 2014. The significant difference in dental decay rates between the two cities presented convincing demonstration of a negative impact on dental decay rates from cessation of fluoridation.
With Edmonton providing control for variables, the conclusion that the caries increase was due to a cessation of fluoridation was fully justified. This is the advantage of having such a control.