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Histograms
A histogram is a useful graph that show the frequency (or counts) of quantitative data, sorted in class intervals or bins.
Watch Out!
Do not confuse a histogram with a bar chart, which is used to showcase categorical data.
A histogram is is a very common graph used to let us see the spread, center, and shape of a distribution of one quantitative variable.
Spread
- What’s the range (i.e. max – min)?
- Does the data cover a large or small range of values?
- This is important when comparing two or more histograms.
Center
- Locate the middle. Where is it?
- The mean and median are both are measures of center. The location of the mean and median depends on the shape.
Shape
- Is the distribution symmetric, skewed, or has no clear shape?
Other observations
- Any gaps? Gaps are empty bins where the frequency is zero.
- Outliers? Outliers are extreme values that a far from the rest of the distribution at either side of the histogram.
- Peaks/modes?
- Unimodal, bimodal, or multimodal?
There are four sections in STAT 100, each with 54 students. The distributions of grades for each section are shown below in histograms.
Which distribution has the highest median grade?
There are four sections in COMM 499, each with 54 students. The distributions of grades for each section are shown below in histograms.
Which distribution shows the greatest variability in grades?
Practice: Histogram
Below is a histogram showing how many glasses of water a person drinks per week (n=168). Which of the following is true? [Select all that apply]
