Quality of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.
Evidence ratings based on Grading quality of evidence and strength of recommendations.
Types of outcome measures
1. ’Incidence’ of colds during regular supplementation was assessed as the proportion of participants experiencing one or more colds during the study period.
2. ’Duration’ was the mean number of days of illness of cold episodes.
1. ’Severity’ of these episodes was assessed in two ways: a) days confined indoors, or off work or off school per episode and b) symptom severity scores.
2. ’Evidence of possible medication side effects’ was available from seven large regular supplementation studies, with the number of participants reporting possible medication side effects in the intervention and control groups.