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Mathematics for Business Decisions, part I. Histograms. Math 115a. Math 115a. Histograms.

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Histograms Business Decisions, part I

Histograms

- A histogram is a table/graph that sorts data into pre-specified categories, or bins.

Math 115a

Histograms Business Decisions, part I

Histograms, Excel 2003

- You can find Histograms in Excel 2003 under:
- Tools
- Data Analysis
- Histograms

- Data Analysis

- Tools
- If you don’t see “Data Analysis” under Tools:
- Go to Add Ins… under Tools
- Select both Analysis Toolpak and Analysis Toolpak-VBA (you may need your original installation disc)

Math 115a

Histograms Business Decisions, part I

Histograms, Excel 2007

- You can find Histograms in Excel 2007 under:
- Data tab
- Analysis group, Data Analysis
- Histograms

- Analysis group, Data Analysis

- Data tab
- If you don’t see the Analysis groupin the Data tab:
- Go to Add Ins… in Excel Options under the Office button
- Select both Analysis Toolpak and Analysis Toolpak-VBA (you may need your original installation disc)

Math 115a

Histograms Business Decisions, part I

Histogram

- You’ll need to specify:
- Input Range
- Bin Range
- Labels (if applicable)
- Output Range

Math 115a

Histograms Business Decisions, part I

Histogram window

- Input Range:
- This is the range of cells that contains the data you want to sort.
- Enter this as a typical cell range in Excel:
A2:A101, e.g.

Math 115a

Histograms Business Decisions, part I

Histogram Window

- Bin Range:
- The range of cells that contain your pre-specified bin ranges (i.e. your categories).
- Enter this as a typical cell range in Excel:
H2:H10, e.g.

Math 115a

Histograms Business Decisions, part I

Bins in Excel

- Again, “bins” are your categories that you want to sort your data into.
- You must specify the intervals that you want, or else you’ll get some odd endpoints!
- Let’s say you want to sort the test scores into the categories 40-49, 50-59, 60-69, … , 90-99.
- You will designate these intervals by the right endpoint for each interval: 49, 59, 69, …, 99

Math 115a

Histograms Business Decisions, part I

Histogram Window

- Labels
- You MUST be consistent:
- Check the box: ONLY if you included the column headers for both the input and bins.
- Leave unchecked: ONLY if your ranges contained only the data, and no headers.

Math 115a

Histograms Business Decisions, part I

Histogram Window

- Output Range
- Input only the cell in which you want the output to START. You should have several clear columns to the right of this cell, and several empty cells below this.
- NOTE: By default, “New Worksheet Ply:” is selected. When you choose “Output Range” it will automatically highlight the “Input Range” space. BE CAREFUL! You click in the box by “Output Range” before selecting a cell.

Math 115a

Histograms Business Decisions, part I

Output

- The output from Excel repeats your bin limits, and also gives the frequency count.
- “More” should be zero. If not, your bin limits did not go high enough to accommodate your data.

Math 115a

Histograms Business Decisions, part I

Choosing appropriate bin limits

- Bins do not need to start at zero!
- Find the range of your data
- range = maximum – minimum

- Your first bin limit should be reasonably above your minimum data point
- Good rule-of-thumb: your first bin limit should be equal to your minimum value + bin width

- Your last bin limit should be greater than your maximum data point

Math 115a

Histograms Business Decisions, part I

Choosing the bin size

- Rule of thumb: start your bin size by the calculation: range of data 10
- Make your endpoints nice numbers, but make sure every bin has the same size interval
- See how your histogram looks:
- If it’s too “blocky”, increase the number of bins by decreasing the bin size
- If it’s too detailed, decrease the number of bins by increasing the bin size

Math 115a

Histograms Business Decisions, part I

Graphing the histogram

- Histograms are typically shown as a column graph.
- Use Excel’s Chart Wizard
- Select Column Graph as the type
- In “Data Range” select only the non-More Frequency cells.
- Click on the “Series” tab and enter the range of cells for labels for “X-axis labels”

Math 115a

Histograms Business Decisions, part I

Labels

- NOTE: Labels will always be centered under each column. Therefore it is not a good idea to label a column by its right endpoint. Labeling by the full interval (i.e. “40-49”) is acceptable only if you have enough room, and not too many bins. Usually it is best to have a column of midpoints for each interval, and label with these. (Remember, the label is centered under each column!)

Math 115a

Histograms Business Decisions, part I

Spacing

- We know grades can range from 0-100. Therefore, it makes sense to demonstrate this continuum of grades by no space between columns:

Math 115a

Histograms Business Decisions, part I

Spacing

- Right-click on any column
- Select “Format Data Series”
- Select the “Options” tab
- Set “Gap width” to zero

Math 115a

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