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What kind of data is shown, so which chart displays it?
More, if you want it
- Tell a from a by whether two measured variables are shown for each unit.
- Name a when a stem asks for the age and sex structure of a population.
- Tell a Kaplan-Meier curve from a by the stepped fall of the proportion still event-free over time.
What does each patient record give?Tap a term: its definition, what you can do with it, and how often the exam asks it.
Definition: touching bars that show how often continuous values fall into each class.
You can: Tell a histogram from a bar chart by whether the bars touch.
Definition: separate bars, one for each category, with length set by the count.
You can: Tell a bar chart from a pie chart by whether each category is a separate bar or a share of a circle.
Definition: a circle divided into slices, one slice for each category's share.
You can: Tell a bar chart from a pie chart by whether each category is a separate bar or a share of a circle.
Definition: one point per person or area for two continuous variables.
You can: Tell a scatter plot from a histogram by whether two measured variables are shown for each unit.
Definition: stacked age bands with males and females on opposite sides.
You can: Name a population pyramid when a stem asks for the age and sex structure of a population.
Definition: a stepped curve of the proportion still event-free over time.
You can: Tell a Kaplan-Meier curve from a histogram by the stepped fall of the proportion still event-free over time.
Each card is one term. The grey line is what the patient says, which is what the question stem gives.
Summary
A histogram shows the frequency distribution of continuous data, with touching bars.
A shows the of , with touching bars. The values are grouped into classes. Each class is a vertical bar, and the bar height is the frequency. The bars touch because the data are continuous.
A mean score on the Hamilton Rating Scale for Depression is a continuous outcome. A histogram can group such scores into classes. A sleep histogram is a different chart. A sleep histogram plots sleep stages across a night and can compare normal sleep with sleep in depression. Continuous data are measured numbers that can take any value, such as blood pressure. Candidates pick a bar chart for blood pressure because both charts use bars. Check whether the values are measured numbers or group names first.
Lowri Pritchard is a public health analyst in a Welsh health board. Lowri says, "I need to show how adult blood pressure is spread across our residents."
Continuous values grouped into classes give touching bars, so the chart is a histogram.
Mnemonic
Sand touches, boxes gap, pie slices, dots pair, pyramid sides, stairs fall. Cue: vertical bars that touch
Sand poured in touching bins is a histogram of continuous values, and separate boxes are a bar chart of categories. Pie slices are shares of a whole, paired dots are a scatter plot of two variables, pyramid sides are males and females on opposite sides, and falling stairs are a Kaplan-Meier curve.
Analogy
Continuous values are sand poured into a row of touching bins, so a histogram has no gaps. Categories are separate boxes on a shelf, so a bar chart leaves gaps between bars.
Where the analogy breaks: histogram classes keep a fixed order along the axis, and bins of sand have no set order.
6 more sections on Charts for data: histogram, bar chart, pie chart, scatter plot, Kaplan-Meier curve and more
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