AP Psychology: Developmental Methods and Physical Development (Drill 13)

Question 1. A developmental researcher recruits 100 four-year-olds in 2010 and tests their vocabulary. She then retests the same children at ages 8, 12, and 16 to track how vocabulary grows with age. Which research design best describes her approach?

• A) Cross-sectional design
• B) Longitudinal design ✓
• C) Case study design
• D) Naturalistic observation

Explanation: The researcher follows the same group of children over many years, which is the defining feature of a longitudinal design. A cross-sectional design would test children of different ages at a single point in time, useful for speed but confounded by cohort differences. The study is not a case study (which focuses on one or a few individuals in depth) and is not naturalistic observation, since the children are being tested rather than watched in their natural environment.

Question 2. A pediatrician notices that a 2-week-old infant, when startled by a loud clap, throws out her arms and then pulls them back toward her body. The pediatrician reassures the parents that this is a normal newborn reflex that typically disappears in early infancy. Which of the following best describes what the pediatrician is observing?

• A) A learned defensive response shaped by prior experience
• B) A reflex present at birth that fades as the nervous system matures ✓
• C) A conditioned response acquired through repeated exposure to loud sounds
• D) An early form of voluntary goal-directed behavior

Explanation: The clap triggered the Moro (startle) reflex, an innate newborn reflex that fades on a predictable timeline as the infant's nervous system matures. (A) and (C) are both wrong for the same underlying reason: reflexes are unconditioned and present from birth, not learned or conditioned through experience. (D) is wrong because reflexes are involuntary and stimulus-bound, not goal-directed.

Question 3. A team of researchers wants to know whether reading ability changes with age. In 2024, they give the same reading test to three groups: 20-year-olds, 50-year-olds, and 80-year-olds. They find that the 80-year-olds score lowest and conclude that reading ability declines with age. Which of the following most seriously weakens their conclusion?

• A) The sample size of 20-year-olds may be too small for statistical power.
• B) Reading ability is partly genetic, which the study did not measure.
• C) The three age groups also differ in the era in which they learned to read, so generational differences in schooling could explain the result. ✓
• D) Longitudinal studies are generally more expensive than cross-sectional studies.

Explanation: This is a textbook cohort effect. Because the three groups grew up in very different educational eras, any difference the researchers find could reflect differences in schooling rather than aging per se, which is the signature weakness of cross-sectional designs. (D) is true but irrelevant: cost has no bearing on whether the conclusion is valid. (A) raises a generic concern not specific to this design flaw. (B) is a real fact about reading but does not explain why the cross-sectional comparison itself is misleading.

Question 4. A neurologist is examining brain scans of a typical 2-year-old and a typical 20-year-old. She notes that the 2-year-old's brain shows an unusually dense network of synaptic connections, many of which will be eliminated as the child matures, while the 20-year-old's brain shows fewer but more efficient connections. Which developmental process best accounts for the difference she observes?

• A) Myelination, which speeds up neural transmission
• B) Neurogenesis, the creation of new neurons in adulthood
• C) Synaptic pruning, in which unused connections are eliminated ✓
• D) Long-term potentiation, which strengthens memory traces in this case

Explanation: The scenario describes a reduction in the sheer number of synaptic connections from early childhood into adulthood, which is the definition of synaptic pruning. (A) is a real and important developmental process happening on a similar timeline, but myelination concerns the insulation of axons, not the number of synapses, the classic true-but-irrelevant trap here. (B) is wrong because neurogenesis refers to the production of new neurons, not the loss of existing synapses. (D) describes a memory mechanism, not a structural developmental change.

Question 5. A researcher reports the following correlations, each computed from a large sample:

• Correlation between child's age (in months, ages 6–24) and number of spoken words: r = +0.82
• Correlation between parental income and child's number of spoken words at age 2: r = +0.35
• Correlation between hours of screen time per day and child's number of spoken words at age 2: r = −0.18

A colleague says, "This shows that giving a child a tablet causes their vocabulary to shrink." Which of the following is the best critique of the colleague's claim?

• A) The study is correlational, so a third variable such as parental involvement could explain the relationship between screen time and vocabulary. ✓
• B) The correlation between screen time and vocabulary is negative, so the claim is directionally incorrect.
• C) A correlation of −0.18 is weak and, even if causal, would not support the strong language "causes their vocabulary to shrink."
• D) The age correlation of +0.82 suggests age is a stronger predictor of vocabulary than screen time.

Explanation: The colleague's core error is inferring causation from correlation, the strongest critique is that a third variable (engaged parents may talk more and also limit screens) could be driving both. (C) is also true, but weakness of a relationship is a separate issue from whether causation can be inferred at all. (D) is true but irrelevant: describing age as the stronger predictor says nothing about whether screen time is causally related to vocabulary. (B) misreads the direction; a negative correlation is consistent with "more screens, fewer words."