Researchers in psychology follow the scientific method to perform studies that help explain and may predict human behavior. This is a much more challenging task than studying snails or sound waves. It often requires compromises, such as testing behavior within laboratories rather than natural settings, and asking those readily available (such as introduction to psychology students) to participate rather than collecting data from a true cross-section of the population. It often requires great cleverness to conceive of measures that tap into what people are thinking without altering their thinking, called reactivity. Simply knowing they are being observed may cause people to behave differently (such as more politely!). People may give answers that they feel are more socially desirable than their true feelings. But for all of these difficulties for psychology, the payoff of the scientific method is that the findings are replicable; that is, if you run the same study again following the same procedures, you will be very likely to get the same results.
Source: Learn Psychology by Dr. Kenneth E Carter, Dr. Colleen M Seifert
It seems like "called" refers to "altering their thinking", but I'm not sure because I've never learnt that "past participle" such as "called" can refer to the part of its entire preceding sentence.
Up until now, I've only learnt that "past participle" can refer to its direct preceding noun.