I concur. "indicate" is fine. "approximate" should be "approximately".
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The word "statistic" does exist and it means a single item in a statistical study. The example sentence results in a mean value, so many items were involved in the study, so there were many statistics. Therefore, the subject can be considered to be plural. The sentence could be written:
Statistics ind
every 22 years within a range of 3 to 4 years
This seems like odd and awkward phrasing to me. How about saying this?
every 18 to 26 years