What is Histogram?

A histogram shows the frequency of occurrence of values in a data set. We group ranges of values into bins. The histogram is an accurate graphical representation of continuous data by using bars of different heights. Histogram lets you analyze the data of underlying distribution. It is also used to check that either data is normally distributed with the help of skewness, kurtosis, and outliers.

Example of Histogram:

The Below table represents the blood cholesterol levels of 40 students. As to determine class size frequencies, it is useful to re-arrange data in increasing order.

Table 1: Cholesterol level of students

213 174 193 220 183 194 200 196
192 200 200 199 178 183 188 193
187 181 193 205 196 211 202 213
216 206 195 191 171 194 184 191
221 212 221 204 204 191 183 227

By Rearranging data into ascending order and we found below values: Minimum value: 171 and Maximum value: 227.

Constructing Histogram:

To construct the histogram from above given continuous data of 40 students, first, we need to split the data into class intervals, which are also called bins. From given data, we have split cholesterol level into bins and each bins represents 10 points, starting from 170.  We tabulate the above data below with their specific sores that contributed to bins.

Bins Frequency Scores included in Bin
170-180 3 171,174,178
180-190 7 181,183,183,183,184,187,188
190-200 13 191,191,191,192,193,193,193,194, 194,195,196,196,199
200-210 8 200,200,202,202,204, 204,205, 206
210-220 5 211,212,213,213,216
220-230 4 220,220,221,227

See the histogram below representing the above data. The histogram represents a continuous data set and notice that there are no “gaps” between the bars, unlike a bar chart.

Hidtogram

What is the difference between a bar chart and a histogram?

The histogram and bar graph is similar but with a distinction that we draw a histogram on a single variable, while we draw a bar graph on two variables. The major difference is that a histogram is used to plot the frequency of a continuous data set in class intervals also called bins. Bar charts are used to plot other types of variables including ordinal and nominal data sets.

Difference between Histogram and Bar Chart

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