Where Does Intelligence Come From? (page 2)
Children's intelligence can be influenced at birth by heredity (genes), prenatal toxins (such as a mother consuming alcohol or drugs during pregnancy), chromosomal defects (such as Down syndrome), or birth trauma (such as lack of oxygen, which may occur for a number of reasons such as having the umbilical cord wrapped around the neck). A child's environment can also have a powerful influence on intelligence. Some children have many opportunities to learn because they are exposed to a wide variety of learning experiences. Other children may have less exposure to new situations and consequently may experience less opportunity for learning. Unfortunately, intelligence can also be lowered by exposure to brain injury (accident) or environmental toxins, including exposure to lead-based paint or drugs such as inhalants.
Although IQ scores can predict academic and later occupational success, merely having a high IQ does not ensure success. Intelligence tests do not measure motivation or other more subtle learning problems, such as difficulties with memory, that might interfere with success.
Remember: IQ scores are considered more stable with increasing age, and IQ scores obtained for preschool children should be regarded cautiously because they are not as reliable. Some young children may score lower than their true ability due to a lack of experiences or fewer opportunities, whereas others may score higher because they live in an environment rich in experiences.
How is the IQ Score Calculated?
The easiest way to understand IQ scores is to relate mental age (MA) or the mental capacity based on the test score, to chronological age (CA), or the actual birth age. For example, if Donny is five years old (CA) but he has the mental age (MA) similar to that of a four-year-old (MA), we would calculate his intelligence score by dividing the MA by the CA and then multiplying the result by 100. In our example, the resulting intelligence score would be 80. Because the average IQ score is 100, then Donny's intelligence score would be below average.
Although the actual mathematical computation of IQ is more complicated, these examples should provide a general idea of what an IQ score means. It is not uncommon for some individuals to be skeptical and concerned about the use of IQ scores in the educational system and how this information might be misused (for example, if a child's IQ score is below average, does that mean the expectations for success will be lower?). Although expectations can influence behavior, the benefits of knowing a child's IQ far outweigh any potential risks. The positive side of knowing an IQ is that it helps us to understand, at a basic level, where a child's problem-solving abilities are in relation to other children at the same age level. Furthermore, as we will soon discuss, IQ is not a single score; the IQ score is actually a composite score based on a number of tests (subtests) that measure different areas of functioning. When we look at the subtest scores, we often can find patterns of strengths and weaknesses that can assist greatly in developing an individualized education program (IEP). Later, we will discuss how the child's initial IEP is developed based on results and recommendations from the initial comprehensive assessment, which often includes intelligence testing.
What do Intelligence Tests Look Like?
The majority of intelligence tests are developed to measure problem-solving skills in two major areas: verbal ability and visual ability. Tasks that measure verbal ability are usually presented orally and require the child to provide verbal responses. Areas evaluated can include measurements of vocabulary knowledge, verbal reasoning, and practical information. Children who score high on verbal tasks usually have better-developed communication skills, good listening skills, and are likely to be avid readers. On the other hand, visually oriented tasks require hands-on performance (completing puzzles, constructing block designs) or visual reasoning (selecting one picture or design from several visual alternatives). Visual tasks require minimal verbal expression. Some visual tasks are timed (using a stopwatch), resulting in either bonus marks for speed or no points for solving the problem after the given time limit.
How Reliable are IQ Tests?
Any test score can fluctuate from assessment to assessment because of many outside factors, such as illness, fatigue, lack of sufficient rapport, or performance anxiety. However, IQ tests are highly reliable and provide results within a 5 to 10 percent range of accuracy. In the psychological report, there should be a statement to the effect that:
There is a 90 to 95 percent chance that the scores reported are a true indicator of the child's ability, and that the child's IQ score falls within the range of ___ to ___.
Because different IQ tests sample different types of abilities, it is possible that a child's IQ on one test can differ from that obtained on another IQ test. In addition, different environmental conditions present at the time of testing can also contribute to variation in IQ scores. Nonetheless, research has shown that individually administered IQ tests are among the most reliable measures that we have and are a strong predictor of a child's ability to learn academic subjects.
What do the Test Scores Mean?
IQ scores can be reported in several ways: standard scores, percentiles, and age equivalents. Each of these scores is obtained by comparing the child's performance with the available range of scores for his or her peer group.
Here Come the Numbers: Put on Your Safety Belts—We Are in for a Numbers Ride!
In this section, we will talk about how scores from IQ tests can help us understand a child's ability in terms of strengths and weaknesses, and help us form possible expectations for performance. Standard scores are a common measurement that allow us to compare scores across a number of different types of assessment instruments.
IQ tests report their scores as standard scores. In our initial example, we discussed how measuring a child's temperature provides a comparison with the normal standard score, which for temperature is 98.6 degrees on the Fahrenheit scale. So regardless of which thermometer you use, the numbers will represent the same scale. Similarly, scores on different tests (for example, achievement tests and IQ tests) can be compared if the scores are all using the same scale. Standard scores are based on the normal distribution of scores that look like the bell-shaped curve presented in Figure 7.1. In this distribution, the majority of scores fall in the middle or the average range. The average score (called the mean) is 100, which falls in the exact middle of the bell. If we were to test 2,000 people, we would find that that 50 percent of the people would score above 100 and 50 percent would score below 100. However, we would also find that the majority of people who took the IQ test had scores that deviated from the mean (called the standard deviation) by 15 points on either side. Roughly 68 percent of the population would score within one standard deviation of the mean:
- 34 percent would obtain an IQ score between 85 and 100 (100 – 15);
- 34 percent would obtain an IQ score between 100 and 115 (100 + 15).
What about 2 standard deviations above or below the mean? How many would score in that area? Well, if we look again at our bell shape, we see that the biggest concentration of population is in the center within one standard deviation on either side. However, as we move toward the ends of the bell on either side, we are losing more and more people. If we looked at these narrow portions under the bell, representing 2 standard deviations (15 + 15) or 30 points from the middle on either side, we would find about 2 percent of the population would score within two standard deviations of the mean:
- 2 percent would obtain an IQ score at or below an IQ of 70
- 2 percent would obtain an IQ score at or above an IQ of 130.