Chapter 2 - Processing and representing Data

Databases

Tables with a collection of data, secondary data

Two-Way Tables contain…

bivariate data

Simple Bar Chart Rules

• Bars are equal width

• Equal gaps between bars

• Frequency on y-axis

Vertical Line Graph

lines instead of bars

Composite Bar Charts

 Composite Bar Charts Has single bars split into different sections

Stem and Leaf Diagrams

A good way of organising data without losing any of the detail

Area of Comparative Pie Chart

Area of Pie Chart = Total Frequency

r₂ equation

CF Step Polygons are used for…

discrete data.

CF Curves are used for…

continuous data.

CF Step Polygon

What bound is used for Frequency Polygons?

upper bounds

Histograms have ________ gaps between bars.

no

For a Histogram with Equal Class Widths…

x-axis = data

y-axis = frequency

Looks like bar charts without gaps.

For a Histogram with Unequal Class Widths…

Area of bar = frequency

Y-axis = Frequency Density (not frequency)

The idea is that the frequency density reflects the ‘concentration’ of things within each range of values.

Histogram triangle Equation

Drawing Histograms

1. Calculate class widths for each class interval

2. Calculate frequency density for each class interval using FD = F/CW formula.

3. Draw a suitable scale on y-axis labelled frequency density.

4. Draw bars using frequency density data. (Remember the bars have no gaps in between)

Common errors in Frequency Polygons

• Midpoints not used

• Joined together at the bottom

• Points not joined together with straight lines but with a curve instead.

Axes and Scales that can be misleading…

• Scales that do not start at zero.

• Missing values on the scales.

• Axes that are unevenly scaled.

• Axes that are not labelled.

• Not using a key.

Positive Skew

Most data values are low.

Negative Skew

Most data values are high.

No Skew

Symmetrical distribution, data values in the middle