histograms?

Question

is the first interval starting point in a histogram the lowest value
from the group?

Answer 1

Histograms, also know as frequency graphs, are tricky. First, it is rare that a single frequency bar represents the number of times a unique value comes up. This results because data values might be scattered all over a wide range of feasible values. In which case, a single feasible value might very well show up once...or not at all. And that's not very useful information for statistical analysis.

For example, suppose we had the following data over a short included interval of all feasible values from x = 7 through 28: ...13,14,14,14,15, 18,17,17,16,16, 17, 17.... The frequency bars would be 1, 3, 1, 2, 4, 1 in magnitude if we counted each unique value. But that would not give much insight into the data distribution.

But if we set del x = 3, we could set one bar on the median x = 14 in the 13-15 interval to a count of 5 and the one on x = 17 in 16-18 to a count of 7. Since the interval of all data runs from 7 through 21, del x = 3 gives us (28-7)/3 = 7 bars of del x width.

Now we begin to see some distribution, which would be especially meaningful if we saw similar bars using del x added to show 3, 4, 5, 7, 4, 2, 2, the seven bars, for example. Now we might begin to expect the data are normally distributed.

So, to answer your question, we used 7 as the low end and 28 the high end of the complete range of the data to figure what del x would be. So the "first interval starting point" is in fact the lowest datum value of the set. And the last interval ending point is the highest datum value of the set.

Answer 2

the first interval is the lowest reported value, BUT, the intervals reported must be equal in range too.

Answer 3

Correct, you start with the lowest value.

Answer 4

yes. it is always zero.