An interval in statistics is a range of numbers that either:
The illustration below shows an example of a chart where the intervals include both endpoints.
An interval like the second one of $5.00 - $9.99 means any compact disk costing $5.00 or more, up to and including $9.99, would be counted in this price range.
A "gap" occurs between $9.99 and $10.00 since there are no coins to represent amounts less then one cent. No amount like $9.993 could be exactly paid for.
The illustration below shows an example of a chart where the intervals include only the bottom endpoint of the range.
An interval like the second one of 130 - 133.5 means any height of 130 or more, up to but not including 133.5, would be counted in this height range.
This is done so that no height is counted twice. A height of 133.5 would be included in the 133.5 - 137 interval but not the 130 - 133.5 interval.
There cannot be a "gap" since a height could always be measured that might fall into one of the gaps.
