1. What Does "IQ" Stand For, and What Does It Mean?

2. "Mental Age"
Alfred Binet,  
Binet was a French psychologist who was intrigued by the varying degree of intelligence he noticed in those around him.
“It's a matter of everyday experience that some people are smarter than others. But how do we measure "smartness?”     

3. "Mental Age"
    In 1905, working with a physician-associate, Theodore Simon, Binet developed the Binet Simon Test designed to measure the intelligence of mentally retarded children, based upon their observations that: (1) Just as children grow taller as they grow older, they grow more mentally capable as they grow older; and (2)  Some children can perform at age and equivalent-grade levels above their chronological ages, while other children perform at age and equivalent-grade levels below their chronological ages.

4. "Mental Age" For example, a few 6-year-olds could perform as well on the Binet Simon mental tests as the average 8-year-old, while a few 6-year-olds could only perform as well as the average 4-year-old.
 In 1911, the concept of "mental age" (as distinguished from "chronological age")
was introduced.

5. "Mental Age"
The 6-year-old who performed as well as the average 8-year-old was assigned a mental age of 8, while the 6-year-old who performed only as well as a 4-year-old was assigned a mental age of 4.

6. What Is "IQ"?
    It was also observed that the gaps between children's mental ages and their chronological ages widened as the children got older.

7. Chronologic age Mental Age
Advanced Child
Delayed Child

8. In 1912, the German psychologist, William Stern, noticed that even though the gap between mental age and chronological age widens as a child matures, the ratio of mental age to chronological age remains constant (and, as we will see, remains essentially constant throughout life).

9. This constant ratio of mental age divided by chronological age was given the name "Intelligence Quotient". Actually, the intelligence quotient is defined as 100 times the Mental Age (MA) divided by the Chronological Age (CA).

10. IQ = 100 MA/CA.
100X Mental age divided by your Chronological age = your IQ
15 X 100 / 15 = 100

11. Mental Age for Adults At approximately
Mental Age for Adults     At approximately. the age of 16, mental age, like height, stops increasing.
Certain mental functions increase slowly and slightly after the age of 16, peaking in the 20's. (vocabulary)

12. The Practical Significance of IQ     
The average IQ of the population as a whole is, by definition, 100.
IQs range from 0 to above 200, and among children, to above 250.

13. The Practical Significance of IQ
About 50% of the population have IQs between 89 and 111,
About 80% of the population have IQs ranging between 80 and 120, with 10% lying below 80, and 10% falling above 120.

14.  "People with IQs between 75 and 90 are 88 times more likely to drop out of high school, seven times more likely to be jailed, and five times more likely as adults to live in poverty than people with IQs between 110 and 125.
A woman with an IQ of 75-to-90 is eight times more likely to become a chronic welfare recipient, and four times as likely to bear an illegitimate child than the Woman with an IQ .”

15. Unemployable. Institutionalized.IQ
Range
Frequency
Cumulative
Typical
Educability
Employment Options
Below 30
>1%
>1% below 30
Illiterate
Unemployable. Institutionalized.
30 to 50
>1%?
>1% below 50
1st-Grade to 3rd-Grade
Simple, non-critical household chores.
50 to 60
~1%?
1.5% below 60
3rd-Grade to 6th-grade
Very simple tasks, close supervision.
60 to 74
3.5%?
5% below 74
6th-Grade to 8th-Grade
"Slow, simple, supervised."

16. 74 to 89
20%
25% below 89
8th-Grade to 12th-Grade
Assembler, food service, nurse's aide
89 to 100
25%
50% below 100
8th-Grade to 1-2 years of College.
Clerk, teller, Walmart
100 to 111
50%
1 in 2 above 100
12th-Grade to College Degree
Police officer, machinist, sales
111 to 120
15%
1 in 4 above 111
College to Master's Level
Manager, teacher, accountant
120 to 125 5%
11 in 10above 120
College to Non-Technical Ph. D.'s.
Manager, professor, accountant
125 to 132 3%
1 in 20 above 125
Any Ph. D. at 3rd-Tier Schools
Attorney, editor, executive.

17. 132 to 137 1%
1 in 50 above 132
No limitations.
Eminent professor, editor
137 to 150
0.9%
1 in 100 above 137
Leading math, physics professor
150 to 160
0.1%
1 in 1,100 above 150
No limitations
Lincoln, Copernicus, Jefferson
160 to 174
0.01%
1 in 11,000 above 160
Descartes, Einstein, Spinoza
174 to 200
0.0099%
1 in 1,000,000 above 174
Shakespeare, Goethe, Newton

19. Can Intelligence Be Measured With a Single Number. Yes and no
Can Intelligence Be Measured With a Single Number?     Yes and no. One of the most serious criticisms of using a single number to assess intelligence is that people may be stronger in certain areas such as verbal skills, logical aptitude or spatial visualization than in others.

20. Drs. Richard Feynmann and Albert Einstein would be examples of geniuses who were extremely strong mathematically while being relatively weak verbally. More  commonly, though, purely intellectual abilities tend to be uniformly high or uniformly low in a given individual, leading to the concept of an underlying "general intelligence" that powers all the specialized intellectual aptitudes.    

21.   
It's also easier to make an IQ score that's lower than your true IQ than it is to make a score that's higher. Taking a test on a bad day, or spending too much time on a few difficult items could artificially lower one's score. The best results are obtained when more than one test is administered.