Table 5 Appraisal of primary studies

Namwongprom et al. [26]

2021

• There are no significant differences in the baseline characteristics of patients recruited (excluding 24 h I-131 uptake and RI status), meaning the effects of confounding factors are minimised

• Appropriate comparison of data using statistical analysis tests (Sample T Test and Kruskal-Wallis H test)

• Clearly defined outcome

• Small sample size of 32 patients

• All patients were recruited from a single institute and are therefore likely to be susceptible to selection bias.

• Study design is retrospective and is thus susceptible.

• No statistical significance or confidence intervals are reported for any outcomes.

• All cases had previously taken ATD which may affect the outcome of radioactive iodine therapy

H Lee et al. [27]

2021

• The efficacy and adverse effects of a wide variety of ATD dosages were explored.

• Relationship between dose of ATD and frequency of adverse events are reported along with statistical significance.

• Clearly defined outcome

• Continuous variable differences were compared with the post hoc Tukey tests

• Small sample size of 99 patients

• Non-randomised allocation of patients, introducing the effect of confounding factors.

• Cases were obtained from only one hospital which may not be representative of the entire population, introducing selection bias

Song et al. [28]

2021

• The largest sample size of 195 of all primary studies included.

• Clearly defined exclusion criteria

• A lengthy mean treatment duration of 4.7 +/- 3.4 years

• Clearly defined definition of remission

• Use of Cox regression model to adjust for confounding at analysis stage

• Over the study period, 28.3% of patients were lost to follow-up.

• Predictors of remission could not be recognised due to inadequate sample size.

Mizokami et al. [29]

2020

• Median follow-up period of 95 months

• Statistical analyses performed using the Mann- Whitney U test or Pearson’s chi square test.

• Accurate assessment of thyroid volumes with the use of ultrasonography

• Small sample size of 117 patients, with concurrent loss to follow-up of 25.6% of patients

• Only a maximal limit of 13.5 mCi of I-131 can be administered to outpatients in Japan, which means activity of I-131 uptake in patients with large goitres is difficult to interpret.

• Variations of TSH levels are likely to have affected thyroid volumes.

• Limited knowledge of the effect of confounding variables due to an absence of a baseline characteristics table