What exactly is the Bell Curve IQ graph and what does it tell us?

Image courtesy of Genius DV

Imagine a group of 1000 people who took an IQ test. In theory, you’d expect more to have an average score than a very high or low score. If you plot all the scores on a chart, it would look a little like a bell.

The bell curve IQ graph is a visual representation of scores of a group of people when they have taken an IQ test.

Let me ask you…

What is your IQ score?

…may be 100, 120 or 140 out of 1000 item scores!

What does it mean?

Frankly speaking nothing unless the score is interpreted by a psychologist in statistical and analytical modes. The bell curve graph is a bell shaped curve utilized by the authors of “The Bell Curve: Intelligence and Class Structure in American Life” to explain differences between different people effectively.

You will discover below the significance of the shape of the graph.

The Significance of the bell curve IQ graph

It is not unusual to see figures represented in columns.

However sometimes you can’t see the significance of the data. Graphs are a very simple way of visually revealing any trend in a group of figures. Consequently the bell curve IQ graph is a perfect representation of the theory on which the IQ system is based.

There are fewer people around who are exceptionally intelligent. These ‘high performers’ will be in the minority, as shown in gray on the right of the bell curve IQ graph above. The same also applies to those with limited intelligence. Those with remarkably high levels of intelligent are seen as genii. It is sad because those with an extremely low level of intelligence usually suffer from some form of mental deficiency. The very low performers, as seen in gray on the left of the graph above, tend to be ‘retarded’ or ‘mentally challenged’.

However the shape of the graph reveals one principal characteristic. The majority of people all have average performance, or an average IQ. That is exactly as you would expect and at the peak of the bell curve IQ graph - IQ score should be 100. This is a graphical representation of the basis for IQ scores as 100 is deemed to be the ‘average’ score. In other words, people of average intelligence will have an IQ of, or around, 100.

Further interpretation of the Bell Curve IQ Graph

It is unusual to have a scale which sees the figures of 0-30 being of little relevance. Anyone with a potential IQ in this range would be mentally incapable of taking the test. Nobody has ever been proven to have a specific IQ in this range. The law struggles with specific values for IQ tests because no two tests are the same. If a candidate takes two IQ tests, their IQ will likely not be identical.  It is accepted that an IQ score has a +/- range of 5%.

In most American states anyone with an IQ of 70 +/- 5% is classed as being mentally challenged. They will not be judged in the same way as someone with an IQ in excess of 75. Those with impaired mental ability are often less aware of the consequences of their actions.

From the late 1990’s it was decided that there would be no upper limit to an IQ score. It had previously been set at 200. However the world has ‘shrunk’ and exceptionally gifted people now have more opportunities to shine. Looking at the bell curve IQ graph you can see that only 0.1% of the population have an IQ in excess of 145. Once an IQ level reaches 160, those people are regarded as genii (geniuses).

What the bell curve IQ graph clearly shows is that approximately 68% of the population have an IQ lying in the range 85 – 115. The ‘super-intelligent’ and those deemed to be of insufficient mental capability makeup 4% of the population. The graph also indicates that everything regarding intelligence in a population balances itself out.

Look at the graph. The number of ‘feeble minded’ people appears to be same as ‘super-intelligent’ people.  This may seem too convenient a result to you. However think about the basis on which IQ scores are measured.

The whole principal of the IQ system is that a score of 100 is taken as an average The bell curve of the graph shows that there are equal numbers on either side of this average score. This must mean there are as many ‘super-intelligent’ people as there are numbers with severe mental disability. It is impossible to know the lowest IQ level. Similarly, the highest IQ cannot be established.

As can be seen form the top ten IQ’s recorded, there is such disparity in the scores. Stephen hawking has an IQ of 160 and is well-known. He is remarkably intelligent. However the top two IQ scores are at 225, which is a massive leap from 160. To balance these scores out, you would need two people with an IQ of -125!

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