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Bias in a sampling method is

(a) any error in the sample result, that is, any deviation of the sample result from the truth about the population.

(b) the random error due to using the chance to select a sample.

(c) any error due to practical difficulties such as contacting the subjects selected.

(d) any systematic error that tends to occur in the same direction whenever you use this sampling method.

(e) racism or sexism on the part of those who take the sample.

You wonder if TV ads are more effective when they are longer or repeated more often or both. So you design an experiment. You prepare $30-$second and $60-$second ads for a camera. Your subjects all watch the same TV program, but you assign them at random to four groups. One group sees the $30-$second ad once during the program; another sees it three times; the third group sees the $60-$second ad once, and the last group sees the $60-$second ad three times. You ask all subjects how likely they are to buy the camera.

(a) This is a randomized block design, but not a matched pairs design.

(b) This is a matched pairs design.

(c) This is a completely randomized design with one explanatory variable (factor).

(d) This is a completely randomized design with two explanatory variables (factors).

(e) This is a completely randomized design with four explanatory variables (factors).