AP Statistics Solution Chapter 4.2 2025 Exam
A University of Helsinki
(Finland) study wanted to determine if chocolate
consumption during pregnancy had an effect on infant
temperament at age 6 months. Researchers began by
asking 305 healthy pregnant women to report their
chocolate consumption. Six months after birth, the researchers
asked mothers to rate their infants' temperament,
including smiling, laughter, and fear. The babies
born to women who had been eating chocolate daily
during pregnancy were found to be more active and
"positively reactive"—a measure that the investigators
said encompasses traits like smiling and laughter.
(a) Was this an observational study or an experiment?
Justify your answer. - Answer-This was an observational study because no treatment was imposed on
the mothers. The researchers simply asked them to report both their chocolate consumption and their
babies' temperament.
An agriculture researcher wants to
compare the yield of 5 corn varieties: A, B, C, D, and
,E. The field in which the experiment will be carried
out increases in fertility from north to south. The
researcher therefore divides the field into 25 plots
of equal size, arranged in 5 east-west rows of 5 plots
each, as shown in the diagram.
(a) Explain why a randomized block design would be better
than a completely randomized design in this setting. - Answer-In a completely randomized design, the
differences in fertility will increase the amount of variability in corn yield for each treatment. However, a
randomized block design would help us account for the variability in yield that is due to the differences in
fertility in the field. This will make it easier to determine if one variety is better than the others.
A University of Helsinki
(Finland) study wanted to determine if chocolate
consumption during pregnancy had an effect on infant
temperament at age 6 months. Researchers began by
asking 305 healthy pregnant women to report their
chocolate consumption. Six months after birth, the researchers
asked mothers to rate their infants' temperament,
including smiling, laughter, and fear. The babies
born to women who had been eating chocolate daily
during pregnancy were found to be more active and
"positively reactive"—a measure that the investigators
said encompasses traits like smiling and laughter.
, (b) What are the explanatory and response variables? - Answer-The explanatory variable is the mother's
chocolate consumption and the response variable is the baby's temperament.
A University of Helsinki
(Finland) study wanted to determine if chocolate
consumption during pregnancy had an effect on infant
temperament at age 6 months. Researchers began by
asking 305 healthy pregnant women to report their
chocolate consumption. Six months after birth, the researchers
asked mothers to rate their infants' temperament,
including smiling, laughter, and fear. The babies
born to women who had been eating chocolate daily
during pregnancy were found to be more active and
"positively reactive"—a measure that the investigators
said encompasses traits like smiling and laughter.
(c) Does this study show that eating chocolate regularly
during pregnancy helps produce infants with good
temperament? Explain. - Answer-No, this study is an observational study so we cannot make a cause-
and-effect conclusion. It is possible that other variables are influencing the response. For example,
women who eat chocolate daily may have less stressful lives and the lack of stress helps their babies to
have better temperaments.
Do smaller classes in elementary
school really benefit students in areas such as scores
on standardized tests, staying in school, and going on
A University of Helsinki
(Finland) study wanted to determine if chocolate
consumption during pregnancy had an effect on infant
temperament at age 6 months. Researchers began by
asking 305 healthy pregnant women to report their
chocolate consumption. Six months after birth, the researchers
asked mothers to rate their infants' temperament,
including smiling, laughter, and fear. The babies
born to women who had been eating chocolate daily
during pregnancy were found to be more active and
"positively reactive"—a measure that the investigators
said encompasses traits like smiling and laughter.
(a) Was this an observational study or an experiment?
Justify your answer. - Answer-This was an observational study because no treatment was imposed on
the mothers. The researchers simply asked them to report both their chocolate consumption and their
babies' temperament.
An agriculture researcher wants to
compare the yield of 5 corn varieties: A, B, C, D, and
,E. The field in which the experiment will be carried
out increases in fertility from north to south. The
researcher therefore divides the field into 25 plots
of equal size, arranged in 5 east-west rows of 5 plots
each, as shown in the diagram.
(a) Explain why a randomized block design would be better
than a completely randomized design in this setting. - Answer-In a completely randomized design, the
differences in fertility will increase the amount of variability in corn yield for each treatment. However, a
randomized block design would help us account for the variability in yield that is due to the differences in
fertility in the field. This will make it easier to determine if one variety is better than the others.
A University of Helsinki
(Finland) study wanted to determine if chocolate
consumption during pregnancy had an effect on infant
temperament at age 6 months. Researchers began by
asking 305 healthy pregnant women to report their
chocolate consumption. Six months after birth, the researchers
asked mothers to rate their infants' temperament,
including smiling, laughter, and fear. The babies
born to women who had been eating chocolate daily
during pregnancy were found to be more active and
"positively reactive"—a measure that the investigators
said encompasses traits like smiling and laughter.
, (b) What are the explanatory and response variables? - Answer-The explanatory variable is the mother's
chocolate consumption and the response variable is the baby's temperament.
A University of Helsinki
(Finland) study wanted to determine if chocolate
consumption during pregnancy had an effect on infant
temperament at age 6 months. Researchers began by
asking 305 healthy pregnant women to report their
chocolate consumption. Six months after birth, the researchers
asked mothers to rate their infants' temperament,
including smiling, laughter, and fear. The babies
born to women who had been eating chocolate daily
during pregnancy were found to be more active and
"positively reactive"—a measure that the investigators
said encompasses traits like smiling and laughter.
(c) Does this study show that eating chocolate regularly
during pregnancy helps produce infants with good
temperament? Explain. - Answer-No, this study is an observational study so we cannot make a cause-
and-effect conclusion. It is possible that other variables are influencing the response. For example,
women who eat chocolate daily may have less stressful lives and the lack of stress helps their babies to
have better temperaments.
Do smaller classes in elementary
school really benefit students in areas such as scores
on standardized tests, staying in school, and going on
