If the referendum unlawful, then some people will not go to vote, simply because they usually avoid breaking the law. The result would be valid (from a probabi

If the referendum unlawful, then some people will not go to vote, simply because they usually avoid breaking the law. The result would be valid (from a probabilistic point of view) if "going to vote" was independent of "voting yes". But if the there is any correlation between "going to vote" and "voting yes" then the result of the referendum will be significantly different than the result of a referendum where any individual was forced to vote. Here there might be a correlation: people in favor or independence or more likely to go voting than others. A similar phenomenon may have happened in the us. If there is a correlation between "lying to polls" and "voting for candidate A" then the poll predictions can become very wrong.