Why pay for a salary survey when you can find information on the Internet for free?  To answer this question let's first of all look at the sources of free salary surveys and the data they contain.  We can then compare them to a well-designed salary survey that you pay for (which we will call a subscription survey) to highlight the differences.

Sources of free salary survey data

There are two main sources:

• Recruitment sites
• Online search sites

The data published by recruitment sites comes mainly from job advertising and/or placement salaries.  The job titles used are often broad and there are rarely job descriptions to help you understand the size of the job.  This often results in the survey quoting very wide salary ranges.  And advertised recruitment salaries are rarely the same as those paid to existing jobholders.

Online search sites usually use information collected from jobholders themselves.  The most common approach is to use a simple on-line questionnaire to collect information from the enquirer about their job and how much they get paid.  This clearly leaves a lot of room for people to interpret the questions differently which can affect the integrity of the data.  The approach also relies quite heavily on people answering questions about their pay accurately.

Subscription salary surveys

A well-designed salary survey will have two key features:

1. A robust way of matching jobs so that the survey compares apples with apples;
2. Data collected direct from employers about real people doing real jobs.

A good survey publisher will also have sound data cleaning processes in place to make sure that data entered into the survey is sensible.

What this means is that the survey results are usually both more usable and more reliable than data provided in free salary surveys. 

In conclusion

Free salary surveys can have their place as a secondary source of market data.  They can help inform pay benchmarking but should be used with care, by people who understand the data and its limitations.  However, they are not a replacement for a well designed subscription salary survey because you may not be able to rely on the job matching or the data integrity.