题目选项分析

A study of high blood pressure treatments found that certain meditation techniques and the most commonly prescribed drugs are equally effective if the selected treatment is followed as directed over the long term. Half the patients given drugs soon stop taking them regularly, whereas eighty percent of the study's participants who were taught meditation techniques were still regularly using them five years later. Therefore, the meditation treatment is the one likely to produce the best results.

Which of the following, if true, most seriously weakens the argument?

【选项】The participants in the study were selected in part on the basis of their willingness to use meditation techniques.