| Training Notes - Screening Data |
Now that the database has been successfully opened, (Hopefully!), many people rush straight into analysis!
Don't!! Do a few simple checks on the data first!
At the present time, where everybody wants everything yesterday, it is also something that often gives immediate results, that can be very useful.
Always do tests like these :-
Map by either Day of the Week or Date.
Map by either Hour, Half Hour or Quarter Hour.
Map using Partition, with a suitable step value. If you think that the field values range from 0 to 100 then 5 would be suitable value.
A simple example illustrates the importance of screening.
Daisy was used to analyse birth weights against post code for all of the births at a large maternity hospital over a year.
On screening the birth weight, it was found that there were large numbers of children born with a weight of 9.99 Kg. Really!!
The response was that the doctors object to filling in the details on the computer! How good was the other data too?
Exercise - Screening a Database
Open a database and screen the fields for expected values.
A fully worked exercise follows.
Screening a Database
A Screening Daisy Chart is in effect the simplest chart, with just one mapping field and no links.
Consider screening the field, Duration in the 'TelephoneCalls' example.
As this is the duration in seconds of a Fax transmission, it should be a low-valued integer between say 5 and 200.But is it?
After opening the database, TelephoneCalls.txt, open the Draw Chart dialog, either from the Draw menu or by using the Control-D keystroke.
The top left of the Draw Chart dialog is shown.
Clicking on Add brings up a series of screens, which setup the mapping field.
In this example, the field, Duration, has been mapped using the Numeric mapping format of partition. A step value of 5 has been set.
Duration appears under Mapping Fields instead of ** None Set.
Show Links in Chart is then unchecked before the chart is drawn.
The chart drawn is shown.
Note that some of the node sizes have been changed to make the chart more readable.
These are adjusted using Setup under Node Style in the Draw Chart dialog.