Hi Simon,
There are 2 techniques called out in the PMBOK Guide in the Control Scope process. See p. 170 of the 6th edition.
1) Variance analysis is used to compare the baseline to the actual results and determine if the difference is within the threshold amount or if corrective or preventive action is appropriate.
2) Trend analysis forecasts future performance based on past results. Over time, it’s used to determine if performance is improving or deteriorating. It can be utilized to recommend preventive actions if necessary.
You’ll see both variance and trend analysis as techniques in controlling scope, controlling schedule, and controlling cost.
Good query, Simon . . . on my exam, I remember several questions about when to use a certain analysis: variance, trend, What-if, qualitative, quantitative, probability distribution, Monte Carlo, etc.
I wish you the best!