It's important to approach research from as many view points as possible, and to be open minded when it comes to embracing a variety of research methods and theories. 
The Singapore Theory (also referred to as the Theory of Familiarization or simply Paranormal Stimuli) is, in essence, really basic. 

The method involves trying to recreate the environment, or a part of the environment, of a particuliar era during an investigation in an attempt to stimulate paranormal activity. The theory is based on familiarisation and the belief that if spirits occupying a location, or in attachment to an object, recognize the environment or something within it, they will become active and possibly show themselves in some form. In the case of residual energy/hauntings, it may be that relevant external factors created by the living could potentially trigger the 'recording' or imprint to play.

 

Playing period music, wearing period outfits, burning oils, incense or using a fragrance familiar to a time period (coal for example or to an individual person (tobacco etc) and the use of trigger objects can all be considered implementation of The Singapore Theory.  More complex implementation may involve the total recreation of a site, using furnishings and anything else possible. In some cases a complete re-enactment/reconstruction of the traumatic event that is believed to have caused the haunting, such as a murder, has been undertaken.