Practice: Measuring Tailedness of Data with the KURTOSIS Functions
This practice shows how to use the KURTOSIS_POP and KURTOSIS_SAMP aggregate functions to measure tailedness of data. Higher kurtosis means more of the variance is the result of infrequent extreme deviations, as opposed to frequent modestly sized deviations. A normal distribution has a kurtosis of zero.
Connect to PDB21 as HR and execute the /home/oracle/labs/M104784GC10/Houses_Prices.sql SQL script to create and populate a table.
Step 2 : Examine the kurtosis of the distribution
Display the table rows. The HOUSE column values refer to types of house that you want to look at and is used categorize the data that you look at statistically and compare with each other.
Display the result of population kurtosis (KURTOSIS_POP) and sample kurtosis (KURTOSIS_SAMP) for the three types of houses.
PRICE_SMALL_CITY has a higher kurtosis compared to PRICE_BIG_CITY. Observe whether there is more data in the tails or around the peak in PRICE_SMALL_CITY and in PRICE_BIG_CITY.
Step 3 : Examine the kurtosis of the distribution after data evolution
Insert more rows into the table.
As you can see, as the number of values in the data set increases the difference between the computed values of KURTOSIS_SAMP and KURTOSIS_POP decreases.
Determine the kurtosis of distinct values in PRICE_SMALL_CITY and PRICE_BIG_CITY.
Is the result much different if the query does not evaluate the distinct values in PRICE_BIG_CITY and PRICE_SMALL_CITY?
The population tailedness value is not different because the same exact rows were inserted.
Insert more rows into the table with a big data set for HOUSE number 1.
Now the tailedness of the data becomes positive for house number 1 which means that data is skewed to right. PRICE_SMALL_CITY has a much higher kurtosis compared to PRICE_BIG_CITY. This implies that in PRICE_SMALL_CITY, more of the variance is the result of many infrequent extreme deviations, whereas in PRICE_BIG_CITY, the variance is attributed to very frequent modestly sized deviations.