17.2.1 Creating Histograms

Create-Histogram

The histogram plots the frequency distribution of a single variable dataset. Histograms allow for a quick assessment of these parameters:

• Dataset center.

• Dataset range.

• Dataset skewness.

• The existence of outliers.

• The existence of multiple modes in the data.

The histogram is produced by splitting the data range into bins of equal size (automatically or by user specification). Bins are the class range (lower boundary ¡Ü bin < upper boundary) for frequency counts. Then for each bin, the number of points from the dataset that fall into each bin is counted. The result is a plot of frequency (i.e. counts for each bin) on the vertical axis vs. response variable on the horizontal axis.

Creating histograms

To create a histogram:

1. Highlight one or more Y worksheet columns (or a range from one or more Y columns).
2. Select Plot: 2D: Histogram: Histogram or click the Histogram button on the 2D Graphs menu.

Origin automatically calculates the bin size and creates a new graph from the HISTGM.OTP template. The binned data is saved in a Binn worksheet (see next). This worksheet contains the bin X values, Counts, (cumulative) Sum, and Percentages.

Accessing the binned data

To access the Binn worksheet:

1. Right-click on the histogram and select Go to Bin Worksheet from the shortcut menu.
2. Double-click to open the Plot Details dialog, click on the Data tab and click the Go button near the bottom of the dialog.

Customizing the histogram

To customize the histogram:

1. Double-click on the histogram, or right-click and select Plot Details.

Both actions open the Plot Details dialog box with the histogram data plot icon active on the left side of the dialog box. The histogram controls are available on tabs on the right side of the dialog box. Binning behavior is determined by controls on the Data tab. Note that some Data tab controls are relevant only to the Box Chart (which shares the Data tab with the histogram).

Controlling the binning

Edit the bin limits by:

1. Clearing the Automatic Binning check box.
2. Edit the Bin Size, and the Begin and End values (see Programming Note, below).
   Or
   Switch the radio box to By Intervals, edit the Number of Bins, and the Begin and End values.

Overlaying a curve on the histogram

To overlay a distribution curve on the binned data (the histogram):

1. Select Normal, Lognormal, Weibull, Exponential, Gamma, Laplace, Lorentz, Kernel Smooth, Poisson or Binomial from the Type drop-down list. The Preview window displays your selection.

See details about the Curve group in the Data tab of Plot Details dialog page.

Create a Histogram + Probabilities

To create a Histogram + Probabilities:

Highlight a single worksheet column (or a range from a worksheet column) and select Plot: Statistics: Histogram + Probabilities or click the Histogram + Probabilities button on the 2D Graphs toolbar.

This menu command/toolbar button plots a cumulative sum of observations in a second graph layer (layer 2).

Additionally, the Histogram + Probabilities menu command types the statistical results -- the mean, the standard deviation, the maximum and minimum values, and the total number of values -- to the Results Log.