Table 3.
Risk of bias within studies.
| Reference | Selection bias | Selection bias argument | Detection bias | Detections bias argument | Attrition bias | Attrition bias argument | Reporting bias | Reporting bias argument | Other bias | Other bias argument | Overall assessment of bias |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Andersson et al. (2003) | Unclear | Randomization method unclear | Low | All outcomes are described and administered online | Low | Attrition is well described and analyses between completers and non-completers are made. | Unclear | No ITT-analyses. | Low | Study appears to be free of other sources of bias | Unclear |
| Berman et al. (2009) | Low | Participants were randomly assigned to either the intervention or WLC via a simple coin toss. | Low | Assessments described and taken online | Low | Imputed score for standardized scales that were missing no less than 10% of the responses, with the exception of the CES-D 10. | Low | All results are reported | Low | Study appears to be free of other sources of bias. | Low |
| Brattberg (2006) | Low | Lottery draw by a study leader who was blindfolded. | Unclear | Outcomes are scarcely described and are administered both by regular mail and e-mail. | Unclear | Attrition is explained. Unclear drop-out analyses. | Unclear | Outcomes are presented. No ITT analyses. | Low | Study appears to be free of other sources of bias | Unclear |
| Bromberg et al. (2012) | Low | Random number table was used for group assignment | Low | All outcomes are described and administered online | High | One outcome measure was not available for analysis. | High | All outcomes are not included, due to a data management error. | Low | Study appears to be free of other sources of bias. | Unclear risk |
| Buhrman et al. (2013a) | Low | Randomization was made by an independent person through a randomization page using at true random number service. | Low | All outcomes are described and administered online | Low | Attrition is well explained and drop-out analyses were made. | Low | All data presented using ITT analyses. | Low | Study appears to be free of other sources of bias. | Low |
| Buhrman et al. (2013b) | Low | Randomization was made through a randomization page using at true random number service. | Low | All outcomes are described and administered online | Low | Attrition is explained and drop-out analyses were made. | Low | All data presented using ITT analyses. | Low | Study appears to be free of other sources of bias. | Low |
| Buhrman et al. (2015) | Low | Randomization was made through a randomization page using at true random number service. | Low | All outcomes are described and administered online | Low | Attrition is explained and drop-out analyses were made. | Low | All data presented using ITT analyses. | Low | Study appears to be free of other sources of bias. | Low |
| Buhrman et al. (2004) | Low | Randomization was done with a dice | Low | All outcomes are described and administered online | Low | Attrition well described. Differences between completers and non-completers are reported. | Low | All outcomes are reported and missing data is imputed. | Low | Study seems to be free of other sources of bias | Low |
| Buhrman et al. (2011) | Low | Randomization was made by an independent person through a randomization page. | Low | All outcomes are described and administered online | Low | Attrition described and analyses of completer and non-completers was made. | Low | All outcome measures were presented according the ITT principle. | Low | Study seems to be free of other sources of bias | Low |
| Carpenter et al. (2012) | Unclear | Eligibility criteria changed during allocation (age). Randomization through random number table. No more information given. | Low | All measures described, participants and administered online | Unclear | No information about why participants dropped out. | High | No ITT-data presented | Low | Study appears to be free of other sources of bias. | Unclear |
|
Chiauzzi et al. (2010) USA |
Unclear | Participants were randomized using an adaptive or “stratified” randomization that ensures group equivalence on preselected variables that may relate to outcome across conditions. The method is not described. No information about allocation concealment insufficient. |
Unclear | No information about how the outcomes were administered. | Unclear | Attrition was described but difference between completers and non-completers is missing. | Low | All pre-specified outcomes were presented | Low | Study appears to be free of other sources of bias. | Unclear |
| de Boer et al. (2014) | Low | Permuted block randomization (ration 1:1; block size of 14). For allocation sequence was concealed from the researcher enrolling and assessing participants in sequential numbered sealed envelopes. | Low | All measures described, participants unidentified. | Low | Attrition was adequately explained and missing data appeared to have been imputed using appropriate methods. | Low | Published report includes data for all expected outcomes | Low | Study appears to be free of other sources of bias. | Low |
| Dear et al. (2013) | Unclear | Randomization via a permuted randomization process. No information of method. Groups differed in the PRSS. | Low | All measures described, participants unidentified | Low | Completers described. Attrition described. ITT (LCOF) |
Low | All pre-specified outcomes were presented | Low | Study appears to be free of other sources of bias. | Unclear |
| Devineni and Blanchard (2005) | Unclear risk | Randomization method unclear | Low | All outcomes are described and administered online | Low | Attrition is well described and dropout predictors are reported | Unclear | All post-data is reported however is not all FU data reported. | Low | Study appears to be free of other sources of bias | Unclear risk |
|
Hedborg and Muhr (2011) Sweden |
Low | Randomization procedure: a sequence of random numbers was generated in statistical package for the social sciences 18.0 (SPSS) software, stratified by gender. Based on magnitude these numbers were arranged into three equal-sized groups, which translated into the three study groups. Blinded randomization. | Low | Outcomes well described and administered online. | Low | Attrition well described and analyses of completers and no-completers reported. | Low | All data reported. ITT for main variables. | Low | Study appears to be free of other sources of bias | Low |
| Hicks et al. (2006) | Unclear risk | Randomization method unclear | Unclear risk | Outcomes were mailed out but unclear how participants sent their responses. | Unclear | ITT analyses were conducted. No information about why participants dropped out. | Low | All expected data is reported | Low | Study appears to be free of other sources of bias. | Unclear risk |
|
Kristjánsdóttir et al. (2013a) Norway |
Low | A computer generated sequence list with the 2 groups randomized in blocks of 4 used for practical reasons to ensure similar numbers in each group at each time point. | Unclear risk | Questionnaires were administered in paper. No description given if outcome assessors were blinded. Outcomes described. | Low | Attrition is described and differences between completers and non-completers are reported. | Low | Published report includes data for all expected outcomes. ITT analyses. | Low | Study appears to be free of other sources of bias | Unclear |
| Palermo et al. (2009) | Low | Fixed allocation randomization scheme was used. Blocked randomization with blocks of 10. An online random number generator was used. Comparable groups | Low | All measures described, participants unidentified. | Low | Completers described. Attrition described. ITT |
Low | All pre-specified outcomes were presented | Low | Study appears to be free of other sources of bias. | Low |
| Ruehlman et al. (2012) | Unclear risk | Randomization method unclear | Low | All outcomes are described and administered online | Low | Attrition was adequately explained and missing data appeared to have been imputed using appropriate methods. | Low | All prespecified outcomes were presented | Low | Study appears to be free of other sources of bias | Unclear |
| Ström et al. (2000) | Unclear | Randomization method unclear | Unclear risk | Some outcomes administered online while other on paper. Unclear if blinding was possible. All outcomes described. | Low | Attrition described and differences between completers and non-completers reported. | High | MLPC not reported in the results. No ITT analyses. | Low | Study appears to be free of other sources of bias | Unclear |
| Trompetter et al. (2015) | Low | Allocation to conditions was performed by sequential block wise randomization using an electronically written key, with stratification on gender, age, and educational level. | Low | All measures described, participants unidentified | Low | Completers described. Attrition described. ITT |
Low | All outcomes were presented. ITT mixed model. | Low | Study appears to be free of other sources of bias. | Low |
|
Williams et al. (2010) USA |
Low | Randomization used 1:1 ratio. A computerized randomization program assisted in the development of the allocation sequence for study. Allocation concealment was utilized to prevent selection bias. | Low | All outcomes adequately described and taken online. | Unclear | Attrition is described but differences between completers and non-completers is not reported | Low | Published report includes data for all expected outcomes ITT analyses. |
Low | Study appears to be free of other sources of bias | Unclear |