Each year, the National Crime Victimization Survey asks a random sample of more than 42,000 households whether they have been victims of crime and, if so, the details. In all, nearly 76,000 people answer these questions. If other people in a household are in the room while one person is answering questions, the measurement of, for example, rape and other sexual assaults, could be seriously ......................................... because the presence of other people in the room could lead to underreporting the true number of sexual assaults (the respondents might be ashamed to speak out). Please, fill in ONE CHOICE (valid / invalid / reliable / unreliable / biased / unbiased).