Study selection

A total of 188 articles were found after a systematic search of all the electronic databases and websites. Out of this, 46 were excluded due to duplication. Then, after assessing the titles and abstract, 126 articles were excluded and 16 articles were found suitable to the systematic review and meta-analysis but after that, 1 paper was excluded as its full text was not found. Finally, 15 papers were found eligible and included in the study for analysis (Fig. 1).

Fig. 1

PRISMA flow diagram showing the study selection process to assess the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023

Description of the included studies to assess the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023

A total of 15,611 school-age children were included in this meta-analysis. The highest sample size included was 10,680, while 73 was the smallest sample size included in the study. The lowest recorded prevalence of iodine deficiency among school-age children based on UIC was 4.3%, in a study conducted in the Shebedino District, South Nation Nationalities and Peoples Region (SNNPR) [31] while the highest was 98.1%, as shown by the study conducted in Hawassa town, SNNPR [32] (Table 1).

Table 1 Description of the included studies to assess the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023Quality assessment of the included studies to assess the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023

NOS quality assessment tool for cross-sectional studies for systematic review and meta-analysis was used to assess the quality of the included studies. As a result, among the 15 articles included, two had satisfactory quality while thirteen had good quality.

Pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023

The pooled prevalence of iodine deficiency among school-age children by using UIC was 58% (95%CI 44.00–77.00). A DerSimonian and Laird random effects model was used to calculate the pooled prevalence as heterogeneity across the included studies was found to be high (I2 = 99.86%, p = 0.00). The standard error for the prevalence values was calculated using a standard formula: \(\sqrt\frac\\ \end}\), where p is the prevalence of the study and n is the sample size of the study. The amount of information each study has contributed to the pooled prevalence based on the sample size was used as a weight. Those studies that had large sample sizes contributed a larger weight (Fig. 2).

Fig. 2

Forest plot showing the pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023

As high heterogeneity was observed in this review, different mechanisms were used to identify the source of the heterogeneity by using different moderators.

Moderators of interest

The moderators of interest used to identify the source of the high heterogeneity in this review were region, where the studies were conducted, and the study year. The region where the studies were conducted was coded as Oromia Region, Amhara Region, SNNPR, and Addis Ababa City administration based on the constitution of the Federal Democratic Republic of Ethiopia. Here, since the studies conducted on iodine deficiency among school-age children in Amhara Region and Addis Ababa City administration were very few (making it difficult to conduct subgroup analysis by this moderator), they were merged with nationally conducted study and mentioned as ‘other’.

Based on the second moderator, study year, studies were categorized as those done before 2015 G.C and after 2015 G.C, as there was a law endorsed in the country that mandates all salt produced or imported into the country to be iodized by 2015 G.C, which may be a source of heterogeneity.

So, to identify the possible sources of heterogeneity, subgroup analysis was performed by the aforementioned moderators such as region, where the studies were conducted, and study year. As a result, heterogeneity in the prevalence of iodine deficiency among school-age children across regions was insignificant (p = 0.843), while the study year was found strongly significant (p = 0.001).

Based on the subgroup analysis result, the highest prevalence of iodine deficiency among school-age children was found in the Oromia Region, which was 64% (95%CI 49.00–79.00) (Fig. 3).

Fig. 3

Sub-group analysis showing the pooled prevalence of iodine deficiency among school-age children in Ethiopia by region, 2023. * “Other” indicates studies conducted in Amhara Region, Addis Ababa City and national study

In terms of the study year, the pooled prevalence of iodine deficiency among school-age children in studies conducted before 2015 G.C. was 85% (95% CI 78.00–91.00) (Fig. 4).

Fig. 4

Sub-group analysis showing the pooled prevalence of iodine deficiency among school-age children in Ethiopia by study year, 2023

To confirm the presence of heterogeneity regarding the study year as a moderator, meta-regression was also done and the study year showed a strongly significant association (p < 0.001) (Table 2).

Table 2 Assessing heterogeneity by study year among studies included to assess the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023 using meta-regression

Sensitivity analysis was done to assess the effect of a single study on the pooled estimate of the study but no single study significantly affecting the pooled estimate of the iodine deficiency among the school-age children was found (Fig. 5).

Fig. 5

Result of sensitivity (leave-one-out) analysis of the included studies to assess the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023

Publication bias

The presence of publication bias or small study effect was assessed by using funnel plots visually and the Egger test statistically. The funnel plot showed that there is symmetric distribution of the studies while the Egger test was insignificant (p = 0.181), implying that there is no publication bias in this study (Fig. 6).

Fig. 6

Funnel plot done to detect publication bias or small study effect in assessing the pooled prevalence of iodine deficiency and associated factors among school-age children in Ethiopia, 2023

Factors associated with the pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023

Six variables, named: age of the children, sex of the children, mother’s education, salt adding time, goitrogenic food consumption, and container used to put salt were extracted from the primary studies. Out of this, goitrogenic food consumption and sex of the children showed an association with iodine deficiency among the school-age children (Table 3).

Table 3 Factors associated with the pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023Association of sex with the pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023

Even though it is not statistically significant, the pooled effect size of the sex of the children was 1.87, which was obtained from five studies [41,42,43,44,45]. Accordingly, the odds of becoming iodine deficient are nearly 2 (OR 1.87, 95% CI 1.43–2.44) times higher among female school-age children compared to male school-age children (Fig. 7).

Fig. 7

Pooled effect size of sex on the pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023

Association of goitrogenic food consumption with the pooled prevalence of iodine deficiency among school-age children in Ethiopia, 2023

The association between goitrogenic food consumption and iodine deficiency was examined by using two studies [43, 45] and found that the odds of iodine deficiency among school-age children is nearly 3 (OR 2.93, 95% CI 1.60: 5.35) times higher among children who had ever consumed goitrogenic foods compared to those who had never consumed them (Fig. 8).

Fig. 8

Pooled effect size of goitrogenic food consumption on iodine deficiency among school-age children in Ethiopia, 2023