## Thursday, 1 September 2011

### A reflection ....

A radar chart, sometimes referred to as a spider chart or star chart, is a circular graph used primarily as a data comparison tool. These charts normally have a circular shape, but can also be displayed as a polygon. Radar charts are useful when you want to look at several different factors all related to one item.
Radar charts have multiple axes along which data can be plotted. In a radar chart, a point close to the center on any axis indicates a low value. A point near the edge is a high value. When you're interpreting a radar chart, check each axis as well as the overall shape to see how well it fits your goals.
Unlike most other chart types, the Radar chart does not plot an X value. Radar Chart X values are ignored for all Radar chart series. However, even though X values are ignored, the X axis is still used for the labels around the chart, as well as spacings between the label, and the chart itself.
– Demonstrate the total performance of one group.
– Display easily and clearly the relationship of different groups.
For the radar chart, the following statistics are calculated:
Mean: the average of all the values in the series.
Maximum the maximum value in the series.
Minimum the minimum value in the series.
Sample Size the number of values in the series.
Range the maximum value minus the minimum value.
Standard Deviation Indicates how widely data is spread around the mean

OLAP CUBES:
OLAP (Online Analytical Processing) is a methodology to provide end users with access to large amounts of data in an intuitive and rapid manner to assist with deductions based on investigative reasoning.
Cube: A data structure that aggregates the measures by the levels and hierarchies of each of the dimensions that you want to analyze. Cubes combine several dimensions, such as time, geography, and product lines, with summarized data, such as sales or inventory figures. Cubes are not "cubes" in the strictly mathematical sense because they do not necessarily have equal sides. However, they are an apt metaphor for a complex concept.
OLAP cubes are multidimensional tables that: are interactive; can be sorted by rows, columns, layers and can be created to accommodate end-user needs. One of the practical examples of OLAP cubes creating reusable SPSS syntax like the one we have seen in class today.

BUBBLE CHARTS:
A bubble chart is a type of chart where each plotted entity is defined in terms of three distinct numeric parameters. A bubble chart is a variation of a scatter chart in which the data points are replaced with bubbles, and an additional dimension of the data is represented in the size of the bubbles. Just like a scatter chart, a bubble chart does not use a category axis — both horizontal and vertical axes are value axes. In addition to the x values and y values that are plotted in a scatter chart, a bubble chart plots x values, y values, and z (size) values.
You can use a bubble chart instead of a scatter chart if your data has three data series that each contain a set of values. The sizes of the bubbles are determined by the values in the third data series. Bubble charts are often used to present financial data. Different bubble sizes are useful to visually emphasize specific values. To create a bubble chart, arrange your data in rows or columns on a worksheet so that x values are listed in the first row or column and corresponding y values and bubble size (z) values are listed in adjacent rows or columns.

References:
http://searchdatamanagement.techtarget.com/definition/OLAP
http://en.wikipedia.org/wiki/Bubble_chart