Primary variables in my experience:

1. State of mind – calm, peaceful, focused  Note Meta Analysis of Free Response Noise Reduction
   1. Simple nervousness from participation in a study could affect the mental state to a significant degree and confound the ability.  I am much less focused and have more busy thoughts when I am nervous or feel performance anxiety.
   2. Need a special set of exercises which help subjects relax and negate anything like performance pressure.  To me the best study designs would be able to elicit and identify a psi event without revealing the purpose of the study.
   3. Belief systems of participants could be a factor for randomized populations.  If the subject has concerns about the ‘sinfulness’ or religious acceptability of these types of abilities, they may be invested in not producing a result.
   4. I recently started taking anti-anxiety meds (Zoloft) and have noticed that echos of future events are coming in a little clearer.  I think this is because there is less background noise or dwelling on items of concern in my thoughts.  This causes me to wonder if giving anti-anxiety meds to those who are not clinically impaired could give them a boost in focus or concentration.
   5. I suspect that alcohol or similar depressants could reduce sensitivity.  I cannot recall any psi events while under the influence enough to be tipsy.
   6. Caffeine or stimulants may create too much mind chatter.  I do usually have a small amount of caffeine in the morning.  This does not seem to have a negative effect.  Too much and my mind is buzzing with too much activity.  I have heard some say that nicotine helps them focus, but since I have only heard that from people who are habituated to it I suspect it would be much the same as caffeine.
   7. Anything that calms and focuses the mind should help, like chamomile, kava kava, tryptophan, maybe even melatonin.  I have noticed that when I take melatonin and then do some meditative exercised before going to bed, I have a strong visual kaleidoscope effect when I close my eyes.  Then I will usually have very vivid dreams.
      1. While some psychedelics may open mental doors to a wider awareness, I have never personally had any psi events while under the influence back in college.  In my experience, LSD and psilocybin remove the usual filters that our brains use to reduce the huge flow of sensory information that our various receptors generate.  Then this overload of information competes for attention and reactions which confuse the processing or interpretive part of the brain.  At that point, those who need everything to make sense become unstable.  Since I have an intuitive compass that lets me absorb the chaos without feeling lost in it, this was not a problem for me.  In fact, some told me that I seemed much like my usual self while tripping.  I would think that only a very focused and disciplined person would be able to ignore the noise and notice the event in the midst of overwhelming sensation.  I would not recommend use of psychoactive substances, except perhaps as a way to disrupt the ability once identified.
   8. I believe meditation would help, but that usually requires some training and practice to get into a receptive state of mind.  Would be worth the investment once a group of sensitive people is identified through other means.
   9. Trans-cranial stimulation may be able to enhance psi abilities.  I saw a documentary about such research that seemed to produce savant abilities and enhanced awareness and processing.
2. Emotional impact.  Could be some kind of threat to a close other or self.  See appendix for specific cases from my own experience.
   1. Minor warnings that relate directly to my own mishaps that will occur within the next hour.
   2. Vague abstract feelings about friends having major life events.  Seem to be a heads up to contact them.
   3. I have clear feelings of loss for family members who will die within about six months or so.
   4. Strong feelings of impending danger or loss for close friends months in advance.
   5. Pushes/soft compulsions that cause me to be in the right place at the right time for special opportunities
   6. Finding things I did not loose. This one is just odd.
3. Proximity in time
   1. Minor events echo in very short time spans.  A warning would be closer in time for minor events and farther away for major ones.  For family deaths, I usually know about 6 months in advance.
4. Proximity in space
   1. I usually have to be near someone or something to catch an echo of a future event.
      1. For example:  when I saw my uncle at a family gathering, I felt he would likely die in about six months.  He had some health problems, but nothing major was shared with the family.  Right at about six months he was put on a transplant list.
      2. In one case, when I drover over a spot, I got a strong impression of a specific type of car wreck.  The next day there was that exact type of wreck in that exact spot.  I was surprised by this one as I had no emotional connection to the event, but there was proximity in space and time.  So I believe you need at least two strong variables to allow an echo to come through the background noise.
5. Correlation of multiple factors