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Histogram
What is it?
A histogram is a diagram that graphically depicts the variability in a process
or procedure within your agency. When you want to see how a procedure
is working in your organization, you can gather data about that procedure
(such as the amount of time the procedure takes) and create a histogram. The histogram allows you to
see the variation in the amount of time it takes to do that process.
Who uses it?
The team members, the managers.
Why use it?
Discovering and displaying this variation will greatly increase the team's
knowledge about a process.
When to use it?
When you want to see the pattern of variation of a particular process, such
as when you are describing a problem, or during data collection and
analysis.
How to use it:
The steps to create a histogram include:
- Gather the data about the variable you are interested in.
- Look at the data and determine the categories or intervals you will
use to organize the data. For example, if you are measuring the number of
weeks it takes to receive an order of contraceptives, "number of weeks of
waiting time" is the data category.
- Construct a frequency table for your data. The frequency corresponds to
the number of times each value is observed. Using the example of waiting
time to receive an order of contraceptives, the frequency table might look
like this:
| Number of weeks
of waiting time | Frequency |
| 1 week | I |
| 2 weeks | I |
| 3 weeks | IIII |
| 4 weeks | IIIII |
| 5 weeks | III |
| 6 weeks | I |
- To draw the histogram, first draw horizontal and vertical axes.
The horizontal axis (X) has the data categories (such as time, or a
measurement, like weight). The vertical axis (Y) represents the frequency
of the observations (the number of observations for each category).
- For each category of data, draw a rectangle (without space between the
rectangles). The width of the rectangle represents the interval between two
groups, and the height represents the observed frequency.
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