The Sheep-Goat Effect is a specific effect which, at its simplest, people who believe in psi or are psi-positive score better on psi tasks than people who do not believe in psi. If you ask someone to perform a psychic task, and they believe psychic powers are hogwash, they're not going to succeed at the task. It's no different than playing pickup basketball, and someone picks the kid in gym that isn't all that athletic, and he says, "I'm really not that good at basketball," and he ends up failing miserably, as almost a self-fulfilling prophecy. Perhaps he would have done better if he actually tried, but the lack of confidence definitely impedes on his will to do well and play with skill.
Specifically, the Sheep-Goat Effect predicts a positive correlation between belief in psi, and standardized score on a psi-task such as ESP. If guessing were completely random, we would expect there to be no relationship between belief and performance (alas, if psi didn't exist, there would be no relationships between any variables and performance for a sufficiently large experiment). For a modern assessment of this, I suggest Walsh & Moddel 2007 - Effect of Belief on Psi Performance in a Card Guessing Task, Journal of Scientific Exploration, Vol 21 No 3, p 501-510.
Psi Missing is a phenomena in which adamant disbelievers in psi will score worse than the mean-chance expectation (MCE), to a statistically significant degree. This effect is contentious even within the parapsychology community. Radin 2002 - Preliminary Analysis of a Suite of Informal Web-Based Psi Experiments, shows this effect, a lot of other experiments don't. Psi missing is a TYPE of Sheep-Goat Effect, but not all Sheep-Goat Effects entail Psi Missing.
Experimenter Effects, also sometimes designated at Experimenter Psi, are effects where the beliefs of the scientist conducting the experiment and/or interacting with the subjects correlate with performance. This is the closest thing to "bad energy," "negative vibes," "harshing my buzz," that many psychics and pseudopsychics use as an out, and may or may not have an impact on performance. This is also very contentious in the parapsych community. Roe & Davey 2006 - Experimenter Effects in Laboratory Tests of ESP and PK Using a Common Protocol (JSE Vol 20 No 2), showed this, as well as Schlitz & Wiseman 1997 - Experimenter Effects and the Remote Detection of Staring (J Parapsych, Vol 61), however a repeat by Schlitz & Wiseman failed to replicate the effect (I don't have that one). It has been attributed to everything from the warmth and optimism of the greeter of the subjects as they enter the experimentation room, to confirmation/data bias, to the psi of the experimenter affecting the experiment, to straight up Bad Vibes. We honestly don't know. Many practicing psychics have argued that if they (other psychics) had better control over their abilities, and were better at shielding, grounding, and centering, the (energetic/psi) influence of skeptics in the room (by itself) should not affect the outcome, and is thus a bit of a crutch/excuse. However, this is totally different from when people degrade or insult the psychic, and wear down their confidence. This has nothing to do with psi and everything to do with confidence and human nature. I think even professional basketball players would be more likely to brick if someone yelled, "YOU SUCK!" as they stepped up to the foul line.
Now, no one has any excuse for using the term, "Sheep-Goat Effect" incorrectly (you know who you are). Have a good day
