Using patterns to categorise postcodes in to postal area

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In last months worksheet we applied a pattern to validate or transform a quantity response during an interview. We will now look at applying a pattern at analysis stage. This particular example uses a derived variable in conjunction with a pattern to extract the postal area part from a full UK postcode.

This example uses the Snap WebHost edition of the Crocodile survey which is provided with Snap.

In this example, we will use a literal response, open ended question. This question has a source pattern of ‘Postcode UK’ applied. This pattern is pre-loaded within Snap and may be used to validate replies to literal response questions representing UK postcodes.

The UK postcode standard is made up of four components; Area, District, Sector and Unit. Each component is then broken down to accept a particular literal response as detailed in the table below:

Component	Acceptable Literal Response	Example
Area	{letter} {letter}{letter}	B12 4LT BS35 3UW
District	{digit} {digit}{digit} {digit}{letter}	BA3 4HT BS35 3UW SW1Y 4RF
Sector	{digit}	BS35 3UW
Unit	{letter}{letter}	BS35 3UW

Step by step

Step 1

The first step is to create a new pattern that will extract postcode area from a full UK postcode.
Enter zip / postcode

Variable Properties | Postcode uk

Select Tailor | Patterns from the main Snap toolbar.
Scroll down to the ‘Postcode UK’ pattern and highlight it.
Click [Clone] to make a copy of it.
Name the new pattern as UK Postal Area.
Click in the Result box and clear the details. Right click, from the menu, select Component and then area, will then appear in the Result box.
To test the pattern, click the button and type a postcode in the text box. If set up correctly, the result box should display just the area component of the postcode.
Click to exit the pattern test and then click again to save your pattern.

Step 2

The second step is to create a derived variable that can be used in conjunction with the UK Postal Area pattern that you have created above.
Pattern Match

Select the Variables icon from the main Snap toolbar.
Click the icon to create a new variable. Make a note of the name and enter ‘Area’ as the Label
The Type will be Derived and the Response will be Single.
In the bottom half of the screen, double click in the Label column, and add a code label of Birmingham.
Use the Tab key to move across to the Values column.
Type Q11 as UK Postal Area ==”B”
Birmingham postcodes contain the letter B as the area component, e.g. B12 4LT. A value of Q11 as UK Postal Area =”B” will count any postal area containing B e.g. BS35 3UW which is a Bristol postcode. Therefore it is necessary to search for an exact match using = =.
Tab again for the next code label which will be Bristol.
The value will be Q11 as UK Postal Area =”BS”
Tab again for the next code label which will be Reading.
The value will be Q11 as UK Postal Area =”RG”
To run the variable, click which will display the results in the Counts column.
Click to save the derived variable.You can then use this new variable to create tables and charts.