1-2s

Random or systematic

A single control observation is outside the ±2SD limit.

When used as a rejection rule, 1-2s yields a high proportion of false rejections.

1-2.5s

Random or systematic

A single control observation is outside the ±2.5SD limit.

N/A

1-3s

Random or the beginning of large systematic

A single control observation is outside the ±3SD limit.

While a value outside ±3SD may be statistically significant, it may not be biologically or medically relevant due to the fact that modern laboratory instruments are often more precise than what is needed medically.

1-3.5s

Random and may also indicate systematic

One control value exceeds the mean ±3.5SD.

This rule is applied within the run only.

1-4s

Random and may also indicate systematic

One control value exceeds the mean ±4SD.

This rule is applied within the run only.

1-5s

Random and may also indicate systematic

One control value exceeds the mean ±5SD.

This rule is applied within the run only.

2-2s

Systematic

Two consecutive QC results are outside the ±2SD limit on the same side of the mean.

N/A

2 of 3-2s

Systematic

Two of three levels of control within the same run exceed ±2SD on the same side of the mean.

This rule is a variation of the 2-2s rule and is applicable when testing three or more levels of control material.

R-4s

Random

There is at least a ±4SD difference between control values within a single run.

Bio-Rad software uses the exact within-run difference between control values to determine if R-4s is violated.

3-1s

Systematic

Three consecutive results exceed ±1SD on the same side of the mean.

N/A

4-1s

Systematic

Four consecutive results exceed ±1SD on the same side of the mean.

N/A

7-T

Systematic

Seven consecutive data points for a single level of control show either a "strict" increasing or decreasing pattern.

A "strict" increasing pattern is defined as a series of points that increase incrementally from the previous point (each point greater than the last) without a break in the pattern. A "strict" decreasing pattern is the same pattern in the opposite direction.

7-x, 8-x, 9-x

Systematic

X number of consecutive results on the same side of the mean.

Because of the extreme sensitivity of these rules, they should be used sparingly, if at all.

10-x

Systematic

Ten consecutive results on the same side of the mean.

This rule has a lower probability for false rejection than do the 7-x, 8-x, and 9-x rules.

12-x

Systematic

Twelve consecutive results on the same side of the mean.

This rule has a lower probability for false rejection than do the 7-x, 8-x, 9-x, and 10-x rules.