This is just statistics. Those 3 things are distinct things in statistical parlance. The 112 number is the sample mean of a given sample. The 100 is the estimat

This is just statistics. Those 3 things are distinct things in statistical parlance. The 112 number is the sample mean of a given sample. The 100 is the estimate of the population mean. If you give a subset of a population an IQ test, the average of all those results isn't going to be exactly 100, because sample means differ from population means due to sheer noise not to mention sampling bias. You might get 98 or 112. Assuming no bias (such as selection bias), the expected value of the sample mean will asymptote to 100 as you increase the sample size. Likewise if you measure the average height of a group of people, you may get a sample mean of 5'9.6, but it won't be exactly 5'10 or whatever the population mean happens to be in the country at large, again due to noise or sampling bias.