Archive | Statistics

Frequency Polygons

Frequency polygons show the same information as bar charts, with points joined by lines instead of with vertical bars. Suppose we need to draw a frequency polygon for the data in the table below which contains information about the weights of some ambitious slimmers. Weight,in kg Frequency 12 35 76 80 41 17 The frequency […]

Sampling Methods

Gathering statistics involves time and effeort. It is a necessary procecdure – governments need to know how many schools to build, or policemen to employ, and companies need to know which products people will buy. They could go out and ask everyone, but this would mean a lot of time and effort needed to be […]

Moving Averages

Moving averages allow us to identify a trend when we have quantities that flucutate over time. For example, ice cream sales may fluctuate by season, with higher sales in the summer and lower sales in the winter. By finding the moving average it becomes much easier to find out if ice cream sales are increasing […]

Pie Charts

60 children go to school. There are various methods they use – they may walk, go by car, bus or train. The statistics are in the following table. Method of Going to School Frequency Angle Walk 21 Car 15 Bus 20 Train 4 Total 60 360 Because it is for a pie chart, the angles […]

Five Figure Summaries and Boxplots

A five figure summary is a set of five numbers that summarises a list of data. It constants of the smallest value, the lower quartile, the median, upper quartile and largest value. A boxplot us a simple diagram to illustrate this visually. Boxplots make comparison between two groups easy. We can draw boxplots for each […]

Histograms

A histogram is a type bar chart using intervals on the x -axis, with the modification that the interval sizes are not fixed. The frequencies are defined by the areas of the bars, and the y – axis is not a frequency axis, but a frequency density axis. A histogram is better able to represent […]

Finding the Mean of a Frequency Table

To find the mean of a list of numbers we add the numbers up and divide by how many numbers there are. For example the mean 1, 4, 6, 6, 7 isHowever sometimes we have a list in the form of a table. The table below is a fictitious summary of the number of goals […]

Designing a Good Questionaire

Questionaires are designed to gather all the relevant information as quickly as possible. The question(s) on a questionaire should be short, simple, eliciting a yes or no answer, or so phrased that the answer enables a mark to be made to indicate that the answer is in one of several categories. The categories should be […]

Tally Tables

Tally tables are a convenient way to sort an unordered list and present it in a frequency table without having to reorder the list. The list is to be sorted into class intervals, and for each entry in a class interval a line is written in a box. Each fifth line is written as a […]

Comparing Boxplots

When comparing boxplots for the similarities or differences between two sets of data, consider the following: the ranges of the data of the sets the maximum and minimum values of the two sets the interquartile ranges of the two sets are the boxplots skewed in any way relative to one another? The boxplot below summarises […]