The extended stats aggregation returns a few more statistics in addition to the ones returned by the stats aggregation:

GET bigginsight/_search
{
 "aggregations": {
    "download_estats": {
      "extended_stats": {
        "field": "downloadTotal"
      }
    }
  },
  "size": 0
}

The response looks like the following:

{
  "took": 15,
  "timed_out": false,
  ...,
  "hits": {
    "total" : {
      "value" : 10000,
      "relation" : "gte"
    },
    "max_score": 0,
    "hits": []
  },
  "aggregations": {
    "download_estats": {
      "count": 242835,
      "min": 0,
      "max": 241213,
      "avg": 9049.102065188297,
      "sum": 2197438700,
      "sum_of_squares": 133545882701698,
      "variance": 468058704.9782911,
      "std_deviation": 21634.664429528162,
      "std_deviation_bounds": {
        "upper": 52318.43092424462,
        "lower": -34220.22679386803
      }
    }
  }
}

It also returns the sum of squares, variance, standard deviation, and standard deviation bounds.