Table 6.
Risk of bias - Elder 2006
| Item | Description | Reviewers’ judgment |
|---|---|---|
| Sequence generation | Quote: ‘… following a screening evaluation, the GCRC data manager randomly assigned participants who met the inclusion criteria to either the GFCF or a placebo diet’ (p.417, col.3). No further details given. Comment: Sequence generation probably done adequately, although no information available on method of randomization | It seems probable that the allocation sequence was adequately generated |
| Allocation concealment | Comment: Not possible to assess since no details given on method of randomization | Insufficient information to decide whether allocation was adequately concealed |
| Blinding of participants, personnel and outcomes Assessments should be made for each main outcome (or class of outcomes) | Quote: ‘Children, parents, and all of the investigative team except for the data manager and dietician were blind to the dietary order’ (p.417, col.2). Quote: ‘Before unblinding, parents were asked to comment on whether they thought their child was on the GFCF diet the first or second 6 weeks. Five were correct, two had ‘no idea’, and six were incorrect’ (p.418, col.2). Comment: Probable that all except data manager and dietician were blind to allocation. Adequacy of blinding was tested satisfactorily for the parents | Knowledge of the allocated interventions was adequately prevented during the study |
| Incomplete outcome data Assessments should be made for each main outcome (or class of outcomes) | Quote: The authors state that, of the 15 randomized, ‘thirteen of the children completed the 12-week protocol’ (p.416, col.1). They ‘. . employed a missing at random model for the three of 15 subjects whose week 12 or week 6 data were incomplete on a major variable’ (p.418, col.2). Comment: Additional information that might support the use of a ‘missing at random’ model was not provided | Unclear |
| Selective outcome reporting | There was no indication that outcomes were reported selectively | The report of the study were free of suggestion of selective outcome reporting |
| Other sources of bias | Authors note a number of limitations to the study including that: (a) the sample was small in size and was heterogeneous ‘possibly contributing to a Type 2 error’ (p. 419, col.1) (b) there was occasional noncompliance with ‘several reports of children ‘sneaking food’ from siblings or classmates’ (p.419, col.1) (c) the duration of treatment was relatively short (12 weeks), given that there are ‘clinical reports of some children who respond to the GFCF diet quickly, while others take several weeks before behavioral effects are detectable’ (p.419, col. 2). (d) the possibility of a placebo effect Each of these has the potential to introduce bias | Apart from the potential sources of bias acknowledged by the authors, the study was apparently free of other problems that could put it at a high risk of bias |