GLOSSARY OF TERMS

O

Observational study (synonym: non-experimental study)
A study in which nature is allowed to take its course. Changes or differences in one characteristic (e.g. whether or not people received the intervention of interest) are studied in relation to changes or differences in other(s) (e.g. whether or not they died), without the intervention of the investigator. There is a greater risk of selection bias than in experimental studies (randomized controlled trials).

Odds ratio (OR)
The ratio of the odds of an event in the experimental (intervention) group to the odds of an event in the control group. Odds are the ratio of the number of people in a group with  an event to the number without an event. Thus, if a group of 100 people had an event rate of 0.20, 20 people had the event and 80 did not, and the odds would be 20/80 or 0.25. An  odds ratio of one indicates no difference between comparison groups. For undesirable outcomes an OR that is less than one indicates that the intervention was effective in  reducing the risk of that outcome. When the event rate is small, odds ratios are very similar to relative risks.

Open clinical trial

1. A clinical trial in which the investigator is aware which intervention is being given  to which participant (random allocation may or may not be used).
2. A clinical trial in which the investigator decides which intervention is to be given  (non-random allocation). Also called open label design.
3. A clinical trial with an open sequential design.

Open label design
A trial in which the investigator decides who receives which intervention rather than using random allocation. See also open clinical trial