Which statement best describes a mixed normal distribution?

Which statement best describes a mixed normal distribution?

• A. It has lighter tails than a normal distribution.
• B. It is indistinguishable from a standard normal distribution.
• C. It is contaminated by a small proportion of scores from a different distribution.
• D. It reduces the variance estimates.

Answer: (C)

A mixed normal distribution means the data come from more than one normal distribution—a mixture of normals. In practice, this looks like most observations coming from one normal component, with a small portion coming from a different distribution, effectively contaminating the overall distribution. That idea lines up with the description of being contaminated by a small proportion of scores from a different distribution. This assumption fits a mixed normal better than the other statements because mixing can create bimodality or changes in tail behavior depending on the second component, rather than guaranteeing lighter tails, indistinguishability from a standard normal, or a reduction in variance.

A mixed normal distribution means the data come from more than one normal distribution—a mixture of normals. In practice, this looks like most observations coming from one normal component, with a small portion coming from a different distribution, effectively contaminating the overall distribution. That idea lines up with the description of being contaminated by a small proportion of scores from a different distribution.

This assumption fits a mixed normal better than the other statements because mixing can create bimodality or changes in tail behavior depending on the second component, rather than guaranteeing lighter tails, indistinguishability from a standard normal, or a reduction in variance.