The Fourth of the Seven C’s - Consistency
Consistency is a measure of how stable your data is. To measure this, you need data across different points in time.
Consistency is important, since measuring unstable things will only lead to unstable recommendations. Employee Engagement surveys provide good examples of the importance of consistency. If you ask the exact same questions to your employees every so often, the results you get back will be consistent, so you can most likely use the results to compare one time period to another. But if you re-word things, or make attempts to add new things, then you will likely be making decisions based on inconsistent data.
For example, suppose in one Employee Engagement survey, you ask for the employee to fill in their age by selecting from age bands (ex. 20-30, 30-40, 40-50, 50+). In your follow up survey, you change the way you ask, opting for larger bands (20-35, 35-50, 50-65, 65+). The way the data was collected was inconsistent...