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DEX27: Distribution of drug exposure start dates

This query is used to to provide summary statistics for drug exposure start dates (drug_exposure_start_date) across all drug exposure records: the mean, the standard deviation, the minimum, the 25th percentile, the median, the 75th percentile, the maximum and the number of missing values. No input is required for this query.

Input:
<None>

Sample query run:
The following is a sample run of the query.

-- Oracle
SELECT min(tt.start_date) AS min_date
     , max(tt.start_date) AS max_date
     , avg(tt.start_date_num) + tt.min_date   AS avg_date
     , (round(stdDev(tt.start_date_num)) ) AS stdDev_days
     , tt.min_date + (PERCENTILE_DISC(0.25) WITHIN GROUP( ORDER BY tt.start_date_num ) )
                                     AS percentile_25_date
     , tt.min_date + (PERCENTILE_DISC(0.5)  WITHIN GROUP (ORDER BY tt.start_date_num ) )
                                     AS median_date
     , tt.min_date + (PERCENTILE_DISC(0.75) WITHIN GROUP (ORDER BY tt.start_date_num ) )
                                     AS percentile_75_date
  FROM
    ( SELECT (t.drug_exposure_start_date - MIN(t.drug_exposure_start_date) OVER()) AS start_date_num,
             t.drug_exposure_start_date AS start_date,
             MIN(t.drug_exposure_start_date) OVER() min_date
      FROM drug_exposure t 
    ) tt GROUP BY tt.min_date 
;
Output:
Output field list:
 Field  Description
drug_exposure_start_date The start date for the current instance of drug utilization. Valid entries include a start date of a prescription, the date a prescription was filled, or the date on which a drug administration procedure was recorded.
percentile_25_date
median_date
percentile_75_date

Sample output record:
 Field  Description
drug_exposure_start_date
percentile_25_date
median_date
percentile_75_date
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