Which of these situations best describes a retrospective observational study? a.)
A student flipping a coin and analyzing its outcomes.

b.)
A doctor analyzing the medical history of a person.

c.)
A company using different promotions and analyzing its sales.

d.)
A clinical researcher giving a medicine to a person and analyzing its effects.

The correct answer is D. Elements are randomly selected from equal-sized blocks of the total population is NOT true regarding a randomized block design experiment

From the question we are told that one statement is NOT true regarding a randomized block design experiment.

Where

A) This design has an advantage of controlling for variables that might confound the response is TRUEB)The elements are randomly allocated to treatment and control groups is TRUEC)The sample is divided into participants or subjects and then grouped by a variable of interest is TRUE

D) Elements are randomly selected from equal-sized blocks of the total population is Not True

In conclusion

The all other Options are true except option D which states that Elements are randomly selected from equal-sized blocks of the total population.

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Ais the correct answer