Tableau
Tableau Funtion: WINDOW_VARP()
Tableau Function: WINDOW_VARP( )
Category: Table Calculation Functions
What Is the Function?
WINDOW_VARP() is a table calculation function in Tableau that computes the population variance of an expression within a specified window (partition) of data in a visualization.
Purpose
It measures how much values vary from the mean when the dataset represents the entire population, using the population variance formula (dividing by n).
Type of Calculation
Table Calculation
Statistical dispersion calculation
Operates on aggregated numeric measures (e.g.,
SUM(Sales))Computed after query results are returned to Tableau
Practical Use Cases
Measuring total volatility in full business datasets
Financial performance variability analysis
Comparing dispersion across regions or departments
Population-level KPI monitoring
Building executive statistical dashboards
Supporting advanced statistical modeling
WINDOW_VARP(expression, [start, end])
| Parameter | Type | Description |
|---|---|---|
expression | Column (Aggregated Measure) | The numeric field for which population variance is calculated (e.g., SUM(Sales)) |
start | Scalar (Integer, Optional) | Offset from the current row defining the start of the window |
end | Scalar (Integer, Optional) | Offset from the current row defining the end of the window |
How It Works?
Mathematical Principle
Population variance formula:
Where:
xi = individual values
μ = population mean
n = total number of observations
Tableau’s Calculation Steps:
Aggregates the expression in the window
Calculates the population mean
Computes squared deviations
Divides by n
Returns the variance
Return Value
Data Type: Numeric (Float)
Meaning: Returns the population variance of values within the defined window.
Variance represents the average of squared deviations from the population mean.
When Should We Use It?
Use WINDOW_VARP() when:
Analyzing complete datasets (not samples)
Measuring total variability across all records
Building full-population financial models
Calculating rolling population volatility
Comparing total operational variability
Basic Usage
Calculate population variance across entire partition:
WINDOW_VARP(SUM(Sales))
Column Usage
Calculate monthly sales population variance within each Region:
WINDOW_VARP(SUM(Sales))
Set:
Partition by → Region
Compute Using → Month
Advanced Usage
Rolling 6-Month Population Variance
WINDOW_VARP(SUM(Sales), -5, 0)
Calculates variance for:
Current month
Previous five months
Population-Based Control Limits
Using standard deviation derived from variance:
WINDOW_AVG(SUM(Sales)) +
3 * SQRT(WINDOW_VARP(SUM(Sales)))
Z-Score Using Population Variance
(SUM(Sales) - WINDOW_AVG(SUM(Sales)))
/ SQRT(WINDOW_VARP(SUM(Sales)))
Tips and Tricks
- Use when data represents a full population
- Combine with
SQRT()to derive population standard deviation - Verify Compute Using settings carefully
- Sort time dimensions properly for rolling windows
Common Pitfalls:
Confusing with
WINDOW_VAR()(sample variance)Incorrect partitioning leads to misleading results
Large partitions impact performance
Mixing aggregated and non-aggregated fields
Related Functions
WINDOW_VAR()(Sample variance)WINDOW_STDEVP()WINDOW_STDEV()VARP()(Aggregate function)WINDOW_AVG()WINDOW_SUM()
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1. What is the difference between WINDOW_VAR() and WINDOW_VARP()?
WINDOW_VAR() calculates sample variance (divides by n−1), while WINDOW_VARP() calculates population variance (divides by n).
2. Does WINDOW_VARP() return standard deviation?
No. It returns variance. Use SQRT(WINDOW_VARP(...)) to calculate population standard deviation.
3. When should I use WINDOW_VARP()?
Use it when analyzing a complete population rather than a sample.
4. Can I calculate rolling population variance?
Yes:
WINDOW_VARP(SUM(Sales), -5, 0)5. Is WINDOW_VARP() computed at the database level?
No. It is a table calculation computed in Tableau after the query returns.