The pay for any study is usually determined by the amount of time you spend in the study facility. You are paid for your time and inconvenience, NOT according to the “risk” the study involves. The rate of pay depends on the clinic, and will usually be in the range of US $100-200/UK £70-150 per 24 hours spent in the facility. Visits of less than a few hours during the day will of course pay much less than this. If you become a study “extra” you can probably expect to be paid between $25-100/£20-120, though a very few clinics pay nothing to extras. If you are forced to drop out for personal or medical reasons, clinics will usually pay you a pro rated amount, based on the portion of the study that you completed.
Some clinics will even pay you in full if you are withdrawn for medical reasons related to your participation in the study. Be aware, however, that a very few clinics won\’t pay you at all unless you complete the entire study. Many that do will include a bonus in the pay structure to encourage you to complete the study. They also withhold part of your payment if you fail to return for follow-ups, repeat tests, etc., if they are required. How you are paid and when depends entirely upon the individual clinic. Larger clinical units will normally pay you immediately on the final day of discharge or the last follow-up visit.
Some clinics are not set up for this and you may have to return within one or two weeks to pick up your cheque, or it might be mailed to you (within one to two weeks usually). Nearly all pay by cheque, and most will have an arrangement with a local bank which allows you to cash it there. Sometimes, however, you may have to deposit the cheque into an account, for instance, if it is not drawn on a local bank. Note that experiments in psychology and cognitive neuroscience departments, which can last from several minutes to a few hours per session, usually pay in cash immediately upon completion of the experiment.
It is practically unheard of for a clinic to deduct tax from the study payment, though they generally report your earnings to the government at the end of the tax year.This will almost invariably be the same for most consumer or usability studies. Many clinics in out-of-the-way locations may reimburse volunteers for their travelling expenses during the study, either based on the distance travelled, or on presentation of receipts.