How do you round 18500 to the nearest thousand?

Answer 1

18000

Some would say 19000 but if you want to know why not, read on. Consider the related question of rounding 18.5 to the nearest whole number, 18 or 19. Some people advise you to round up 0.5. Others say round down. The problem with that approach is as follows:

In the first case

If the number is 0.0 you don't need to round

If the number is 0.1, 0.2, 0.3 or 0.4 you round down

If the number is 0.5, 0.6, 0.7, 0.8 or 0.9 you round up

So 4 downs and 5 ups (and one no change).

Net Result: you introduce an upward bias.

In the second scenario, you introduce a downward bias through rounding.

Possible solution:

Round up from 0.5 half the time, round down the other half. That satisfies the bias problem but introduces another - that of reproducibility. If someone else were to look at your data would they round up/down the same way you did? Unlikely. You need a system which will round 0.5 up half the time and down half the time but where the decision is made for you.

Hence the best solution is to round up or down so that the new last digit is even.