Change of behaviour in people after they come to know they are participating in a research project to produce results that do not have validity is known as

The correct option is Hawthorne effect.

Detailed Explanation:
The Hawthorne effect refers to a type of reactivity in which individuals modify an aspect of their behavior in response to their awareness of being observed. This phenomenon was first identified during research conducted at the Western Electric Hawthorne Works in Chicago during the late 1920s and early 1930s.
When research participants realize they are part of a study, they may change their normal behavior (either consciously or unconsciously) to please the researchers, conform to expected outcomes, or simply because of the attention they are receiving. This behavioral change can distort the natural responses of the subjects, thereby producing results that lack ecological or internal validity.

Why other options are incorrect:
- Blind effect: Usually relates to experimental designs (like single-blind or double-blind studies) used to prevent bias, rather than the reactive change in participant behavior itself.
- Evaluation effect: While evaluation apprehension can cause anxiety, it is not the standard term for the general behavioral alteration due to being in a study.
- Demand effect (or demand characteristics): This occurs when participants alter their behavior because they think they have figured out the hypothesis or what is expected of them specifically, which is a sub-type of reactivity but distinct from the broader observation-based change defined by the Hawthorne effect.