Test Q

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

Per effettuare il Test Q al fine di individuare i dati errati, si devono disporre i dati in ordine di valore crescente, e quindi per ognuno calcolare il coefficiente Q, definito come:

${\displaystyle Q_{n}={\frac {|x_{n}-x_{n-1}|}{R}}}$

dove R è l'intervallo in cui abbiamo dei valori

If Q_calculated > Q_table then reject the questionable point.

Tabella di valori

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.

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