Test Q

Template:Traduci Il Test Q (Q-Test, in inglese) è un semplice test statistico per scartare dati ritenuti errati.

To apply a Q test for bad data, arrange the data in order of increasing values and calculate Q as defined:

${\displaystyle Q={\frac {gap}{range}}}$

If Q_calculated > Q_table then reject the questionable point.

Table

Number of Values:	3	4	5	6	7	8	9	10
Q90%:	0.941	0.765	0.642	0.560	0.507	0.468	0.437	0.412
Q95%:	0.970	0.829	0.710	0.625	0.568	0.526	0.493	0.466

Example

For the data:

${\displaystyle 0.189,0.169,0.187,0.183,0.186,0.182,0.181,0.184,0.181,0.177}$ 

Arranged in increasing order:

${\displaystyle 0.169,0.177,0.181,0.181,0.182,0.183,0.184,0.186,0.187,0.189}$ 

Outlier is 0.169. Calculate Q:

${\displaystyle Q={\frac {gap}{range}}={\frac {(0.177-0.169)}{(0.189-0.169)}}=0.400}$ 

With 10 observations at 90% confidence, Q_calculated < Q_table. Therefore keep 0.169 at 90% confidence.

See also: List of statistical topics