An article in the student newspaper “The Varsity” has just published
the results of an online survey into the number of students who use illegal
drugs while at Cambridge. The headline figure of 63% of students having taken illegal
drugs seems very high. Headlines can be misleading however. Firstly, this does
not mean that over 60% of all Cambridge students have taken drugs but only those
that responded to the survey. The article does not give the number of students
who completed the survey so it is impossible to gauge how prevalent drug taking
might be in Cambridge. Percentage figures without an indication of the number
of students who filled in the survey is misleading. If say 1000 students did
the survey, of which 630 had taken drugs to give the 63% headline number, this
would only be 3.5% of the total number of students at Cambridge. It cannot be
assumed that the rate of drug taking will be the same between those students
who completed the survey and those who did not. In surveys of this kind, there
will be a bias for drug takers to want to compelete the survey. Why would
students who do not take drugs be interested in completing a survey that they
would see as irrelevant to them?
The second point is that the headline figure of 63% is a
rather blunt instrument to convey accurately the full details of the survey.
Reading the article more closely suggests that the breakdown of this headline figure
is 61% marijuana, 2% cocaine and less than 1% heroin. Thus, the majority of the
students who use illegal drugs are using the Class B drug, marijuana, rather
than the more serious Class A drugs.
