Concept Practice
Does Aging Affect Intelligence?

Chapter 66. Does Aging Affect Intelligence?

cohort
group of people born at the same historical time
fluid intelligence
a form of intelligence reflecting rapid, flexible thinking on unfamiliar tasks
cross-sectional study
a type of research design comparing people of different ages who are tested at the same historical time
intelligence
mental capacity to learn from experience and adapt effectively to a particular environment
crystallized intelligence
a form of intelligence reflecting effective use of stored knowledge on familiar tasks
intelligence test
way of measuring mental abilities; typically produces a numerical score that allows comparison with other people
development
changes in a person’s thinking and behavior that typically accompany increased chronological age
longitudinal study
a type of research design in which the same individuals (or people from the same cohort) are tested at several different historical times
distribution
arrangement of scores from a variable, showing their observed frequency of occurrence
Does Aging Affect Intelligence?
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Learning Objectives:

Contrast the results of cross-sectional and longitudinal research on intelligence.

Describe the typical pattern of performance on tests of fluid and crystallized intelligence across the years of adulthood.

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The image is a line graph with one line. The X axis is labeled as “Age in years (different individuals)” and ranges from 25 to 70 in increments of 5. The Y axis is labeled as “Score on primary mental abilities test” and ranges from 35 to 60 in increments of 5. The line starts at a score of 52 at 25 years of age, increases to a score of 56 at 35 years of age, and then decreases gradually to a score of 41 at 70 years of age. The approximate data is shown in the following table: Table header: Score on primary mental abilities test. Column 1 header: Age in years (different individuals). Column 2 header: Score. Raw 1 - 25 - 52. Raw 2 - 30 - 54. Raw 3 - 35 - 56. Raw 4 - 40 - 52. Raw 5 - 45 - 51. Raw 6 - 50 - 52. Raw 7 - 55 - 50. Raw 8 - 60 - 47. Raw 9 - 65 - 43. Raw 10 - 70 - 41.

1. As adults get older, does their intelligence increase or decrease? The earliest studies (conducted between 1920 and 1960) found that intelligence peaks in young adulthood, and then drops substantially during middle and later adulthood. This graph shows a typical pattern of results on one type of intelligence test.

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Time of birth Time of Measurement
Cohort 1950
1880 Age 70
1890 Age 60
1900 Age 50
1910 Age 40
1920 Age 30
1930 Age 20

2. However, these early studies used the cross-sectional research design, testing different age groups of people (called cohorts) in the same year. For example, the 70-year-old individuals tested in 1950 had been born in 1880, before compulsory public education existed in the United States. We now realize that the cross-sectional approach fails to consider generational differences in education and other life experiences, so it exaggerates the negative impact of aging.

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The image is a line graph with one line. The X axis is labeled as “Age in years (same cohort)” and ranges from 25 to 70 in increments of 5. The Y axis is labeled as “Score on primary mental abilities test” and ranges from 35 to 65 in increments of 5. The line starts at a score of 54 at 25 years of age, gradually increases to a score of 62 at 60 years of age, and then decreases gradually to a score of 57 at 70 years of age. The approximate data is shown in the following table: Table header: Score on primary mental abilities test. Column 1 header: Age in years (different individuals). Column 2 header: Score. Raw 1 - 25 - 54. Raw 1 - 30 - 53. Raw 1 - 35 - 54. Raw 1 - 40 - 55. Raw 1 - 45 - 56. Raw 1 - 50 - 59. Raw 1 - 55 - 60. Raw 1 - 60 - 62. Raw 1 - 65 - 58. Raw 1 - 70 - 57.

3. Later research using longitudinal studies, which retested the same group of people (same cohort) over many years, produced different results. Intelligence held steady across the adult years, or even increased slightly!

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The image is a line graph with one line. The X axis is labeled “Time of measurement” and includes Time 1, Time 2, and Time 3. The Y axis is labeled “Intelligence test score” and ranges from low to high. The line in the graph shows a gradual increase from medium to just above medium across the three times. A large vertical oval extends equally above and below the point at Time 1, demonstrating a large variability in scores at this time of measurement. Those who are at the bottom of this oval, who scored lower on the test, tended to be unavailable at time 2. A medium vertical oval extends equally above and below the point at Time 2, demonstrating a medium amount of variability in scores at this time of measurement. Those who are at the bottom of this oval, who scored lower on the test, tended to be unavailable at time 3. A small vertical oval extends equally above and below the point at Time 3, demonstrating very little variability in scores at this time of measurement. Those who scored the lowest at time 1 and time 2 are not included in time 3, thus potentially inflating the scores at this last time of measurement.

4. However, we now realize that the results of some longitudinal studies are overly optimistic. Within the distribution of scores at the first time of testing, the individuals with the lowest scores tend to drop out at later testing times. This could artificially inflate the average score at later testing times.

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Screen 6: The image is a line graph with three lines. The X axis is labeled as “Age in years” and ranges from 25 to 70 in increments of 5. The Y axis is labeled as “Score on intelligence test” and ranges from low to high. The first line represents fluid intelligence. This line starts at a high score at 25 years of age and decreases sharply in almost a straight diagonal line to a low score at 70 years of age. There is a sharp decrease in fluid intelligence as we age. The second line represents crystallized intelligence. This line starts at between a low and medium score at 25 years of age and gradually increases in a diagonal line to just over a medium score at 70 years of age. There is a progressive increase in crystallized intelligence as we age. The third line represents overall intelligence. This line starts at a medium score at 25 years of age, rises only slightly and remains steady, decreasing only a little after 60 years of age. It appears that overall intelligence is fairly constant over one's life span.

5. In addition, researchers now believe that even if overall intelligence doesn’t change much across adulthood, it has two subcomponents that do change as we age—in different ways. Fluid intelligence (quick, flexible, abstract thinking) seems to decline in later life, while crystallized intelligence (accumulated knowledge and skills) tends to increase in healthy middle-aged and older adults.

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Practice 1: Describing Cross-Sectional and Longitudinal Studies

Select each button to show a representative example of that type of study.

As people move from young adulthood, to middle age, and then to late adulthood, does their intelligence change? Researchers now realize that the answer to this question depends on how you study the issue.

One method of studying developmental change uses cross-sectional studies, which test people of different ages at the same point in time. The other method uses longitudinal studies, which test the same group of people at different points in time.

Year of Measurement
Year of Birth 1990 2000 2010
1950 Age 40 Age 50 Age 60
1960 Age 30 Age 40 Age 50
1970 Age 20 Age 30 Age 40
Each red cell shows the age of three different groups of people tested in a cross-sectional study. Note that any column in this table would represent a cross-sectional study.
Each blue cell shows the age of the same group of people tested over time in a longitudinal study. Note that any row in this table would represent a longitudinal study.
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Practice 2: Comparing Cross-Sectional and Longitudinal Studies of Intelligence

Select each button to compare the results from the two types of studies.

When used to measure changes across the decades of adulthood, cross-sectional and longitudinal studies tend to produce different results.

The image is an empty graph. The X axis is labeled as “Age” and ranges from 25 to 88 in increments of 7. The Y axis is labeled as “Intelligence test score” and ranges from 30 to 65 in increments of 5. Two buttons appear below the graph: Cross-sectional study and Longitudinal study.
Most cross-sectional studies of adult intelligence show a steep decline with age, especially after about age 40.
In contrast, longitudinal studies generally show that intelligence seems to hold steady or even increase slightly during middle adulthood, with a small decline after the 60s.
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Practice 3: Comparing Fluid and Crystallized Intelligence

Select each of the buttons to compare the results of tasks measuring crystallized and fluid intelligence.

The specific tasks used to measure fluid intelligence and crystallized intelligence also show different patterns of performance across the adult years.

The image is an empty graph. The X axis is labeled as “Age in years” and ranges from 25 to 70 in increments of 5. The Y axis is labeled as “Performance” and ranges from low to high. Two buttons appear below the graph: Vocabulary tasks and Spatial problems.
In general, performance increases on tasks measuring crystallized intelligence (accumulated knowledge such as vocabulary).
In contrast, performance drops on tasks measuring fluid intelligence (rapid, flexible thinking needed on spatial tasks and unfamiliar problems).
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Quiz 1

Drag each term for the method of studying developmental changes to the gray area in front of the appropriate research scenario. When all the terms have been placed, select the CHECK ANSWER button.

Perhaps you should go back to review results of cross-sectional and longitudinal research on intelligence.
Select the NEXT button and move to Quiz 2.
Year of Measurement
Year of Birth 1990 2000 2010
1950 Age 40 Age 50 Age 60
1960 Age 30 Age 40 Age 50
1970 Age 20 Age 30 Age 40

Researchers test people born in 1960 when they are 30 years old, then test them again at age 40 and age 50.

In the year 2000, researchers test people who are 30, 40, and 50 years old.

Results usually suggest that intelligence declines substantially during the adult years.

Results usually suggest that intelligence is relatively stable from young adulthood until very late in life.

cross-sectional
cross-sectional
longitudinal
longitudinal
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Quiz 2

Drag each term for each type of intelligence to the gray area in front of the appropriate description. When all the terms have been placed, select the CHECK ANSWER button.

Perhaps you should go back to review the typical pattern of performance on tests of fluid and crystallized intelligence across the years of adulthood.
select the NEXT button and move to the Conclusion

uses rapid, flexible thinking; tested with timed spatial tasks or abstract logical problems

uses stored knowledge accumulated through education and life experiences; tested with vocabulary or general knowledge tasks

typically declines during the adult years

tends to increase across adulthood, at least until very late in life

crystallized intelligence
crystallized intelligence
fluid intelligence
fluid intelligence
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