Table 2 Risk of bias assessment tool
| Â | Risk of bias item | Yes = 1 No = 0 |
|---|---|---|
External validity | ||
 1 | Was the study target population a close representation of the national population in relation to relevant variables? |  |
 2 | Was the sampling frame a true or close representation of the target population? |  |
 3 | Was some form of random selection used to select the sample, OR, was a census undertaken? |  |
 4 | Was the likelihood of non-participation bias minimal? |  |
Internal validity | ||
 5 | Were data collected directly from the participants (as opposed to medical records)? |  |
 6 | Were acceptable case definitions of iodine deficiency in pregnancy used? |  |
 7 | Were reliable and accepted diagnostic methods for iodine intake utilised? |  |
 8 | Was the same mode of data collection used for all participants? |  |
 9 | Were the numerator(s) and denominator(s) for the calculation of the iodine intake appropriate? |  |
Summary of the overall risk of bias | Low risk | 0–3 |
Intermediate risk | 4–6 | |
High risk | 7–9 | |