Confidence bounds (or intervals) are generally described as one-sided or two-sided.
Two-Sided Bounds
When we use two-sided confidence bounds (or intervals) we are looking at where most of the population is likely to lie. For example, when using 90% two-sided confidence bounds, we are saying that 90% lies between X and Y, with 5% less than X and 5% greater than Y.
One-Sided Bounds
When using one-sided intervals, we are looking at the percentage of units that are greater or less (upper and lower) than a certain point X.
For example, 95% one-sided confidence bounds would indicate that 95% of the population is greater than X (if 95% is a lower confidence bound) or that 95% is less than X (if 95% is an upper confidence bound).
In ALTA, we use upper to mean the higher limit and lower to mean the lower limit, regardless of their position, but based on the value of the results. So for example, when returning the confidence bounds on the reliability, we would term the lower value of reliability as the lower limit and the higher value of reliability as the higher limit. When returning the confidence bounds on probability of failure, we will again term the lower numeric value for the probability of failure as the lower limit and the higher value as the higher limit.
See Also:
Confidence Intervals (or Bounds)
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