I pooled prevalence data using metaprop command in STATA 13. I have found significant heterogeneity between studies and I conducted subgroup analysis to explore the sources of heterogeneity. However, one of the subgroup contains three studies and the I2 statistics result showed a doted sign. So far, I know that the doted sign indicates the I2 test is not applicable. This is true for a single study. In my case even for three studies I detected a doted sign. I am a little bit confused. Anyone who can help me? Here under attached the frost plot of subgroup analysis.

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