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Data

The word 'data' means information in the form of numerical figures or a set of given facts. It can be anything, that is, numbers, words, measurements, observations or even just descriptions of things. There are two types of data: Quantitative and Qualitative.

i. Quantitative (or Numerical) data:

The data which are identified or measured on a numerical scale is known as Quantitative data or numerical data. Ex: Number of students appearing for an AP Statistics examination, the daily temperatures in Death Valley, etc.
Quantitative data can either be discrete or continuous.

The data are said to be discrete, if the values or observations belonging to it are distinct and separate, that is, they can be counted. Ex: Number of members in a family.
The data are said to be continuous, if the values or observations belonging to it are measured or take on any value within the finite or infinite interval. We can count, order and measure continuous data. Ex: Weight, height, temperature, etc.

ii. Qualitative (or Categorical) data:

Qualitative or categorical data are the data that can be classified into a group.
A set of data is said to be a categorical, if the values belonging to it can be sorted according to category. Ex: Gender, eye color, ethnicity, etc.
Qualitative data can be either nominal or ordinal.

The data in which there is no natural order between the categories is known as nominal data. We can count but not order or measure nominal data. Ex: Color of an eye.
The data in which an ordering exists between the categories is known as ordinal data. We can count and order, but not measure ordinal data. Ex: Auto racing.

Dotplot and Bar graph

We have various types of methods for organizing data as well as for arranging data. In order to see patterns and shapes and for presenting an immediate impression of everything about the data, graphical displays are very useful. Generally, we are use Dot plots, Bar charts, Histograms and Stem-plots for representing the data because all the graphical displays should be clearly labeled, leaving no doubt what the picture represents.

Dot-plot: A dot-plot is used to illustrate categorical data i.e., the data which can be classified into a group. It is a very simple type of graph that represents the data values with dots, above the corresponding values on a number line. Refer to the example at the top.

Bar graph:

A bar graph or chart is used to illustrate qualitative data i.e., categorical data. It is a common visual display to compare the frequencies of categories or groups. The horizontal axis in bar graph contains categories and the vertical axis in the bar graph contains frequencies (or relative frequencies). The frequencies of different results are indicated by the heights of the bars representing these results. It is used in agricultural, sports, commercial, scientific data etc.

  • Example: The Centers for Disease Control and Prevention lists leading causes of death in females in the United States during 2009.
    Cause of Death Percent
    Cancer 34.6
    Heart disease 14.4
    Stroke 3.8
    Other 47.2
    The above given data can be displayed in the following bar chart or bar graph.