A student would like to estimate the average number of text messages sent by cell-phone users in a day. Which of the following methods would provide a voluntary response sample?

A voluntary response sample forms when people choose for themselves whether to participate, often by responding to an open invitation. A text poll during a nightly news broadcast lets viewers decide whether to text in, so it is a voluntary response sample. The other methods select people to survey rather than relying on self-selection.

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