Dr. Bloedorn is a health psychologist who researches nutrition. She is curious as to whether a new drink additive will help people consume fewer calories during a meal. The drink additive is a white, odorless, tasteless powder that a person can add to any drink. She plans to collect a random sample of 50 overweight students on campus and measure the calories they eat during lunch, using a calorimeter. She plans to give this additive to the same participants to use at lunch a few days later and measure how many calories they eat (again, using the calorimeter).
The addition of a group that does not use the drink additive but adds a similar-looking substance that they think is the additive would help Dr. Bloedorn address which of the following threats to internal validity?
a. Testing threat
b. Observer bias
c. Instrumentation
d. Placebo effects

In research methods and statistics, mainly there are eight different types of threats associated with the internal validity including experimental mortality, regression, interaction of threats, selection, history, testing, maturation, and instrumentation.

Instrumentation: The term "instrumentation" is described as one of the different types of internal validity threat that encompasses the change in the scores, instruments, or observers that may produce a few changes in the outcomes of a particular study.

In the question above, the given statement represents "instrumentation".