# What is the appropriate measure of average that must be used?

The answer depends on the distribution of the data - in particular, its skewness and the presence of outliers.

### What does the z-value in statistics have to do with the level of confidence?

A z-value by itself, has nothing to do with level of confidence. A z-value can be used to calculate probabilities of observing a result that is at least as far from the mean. That probability measure can be used to calculate the level of confidence but you need to be careful about using the one-tailed or two-tailed measures - as appropriate.

### When is it appropriate to rely on estimation?

Occasionally, estimation must be used to account for objects, like body cells or other very small things. In measurement, techincally, everything is an estimation -- unless it is an integer. How long is the block? Do you measure it to the neaest inch, tenth inch, thousandths of an inch? Reminds me of the question: How long is the coast line of England??