Understanding Control Charts

by | Jun 8, 2021 | Reports

Video Overlay

What are control charts?

Control charts are a visual depiction of ongoing data points that various statistics are applied to.  The EPA used to require a laboratory to adjust its spike acceptance recovery percentage based upon how spikes were recovered over time (typically > 20 recovery events). 

The problem in doing this is that it almost always tightens up recovery limits, making it difficult to maintain production levels due to re-batching and re-analyzing client’s samples. When that went away (due to different requirements from Standard Methods and ASTM) then the charts were used to trend data points.  Trends were applicable to instrument degradation and the improper construction of the spikes.  Generally the only people who see control charts are analysts and anyone assessing their work.  

When and how should control charts be used?

Control charts should be viewed on a continuous basis so that any trends can be caught early and rectified.

The main roadblock to control chart usage is when not all of the data  points are accounted for, or when obvious statistical outliers are included.  Either of these scenarios will skew the data and not let you see trends up or down or trends on either side of the mean.  Active data observation will allow for proper control chart construction.

The SVL Analytical difference

Control charting can be done with a LIMS, Excel, or by hand calculations.  SVL uses their LIMS to provide real time chart creation.  For example, if an LCS came in low, the analyst could pull in all the data since the last LCS was made, to determine if it is a one time event or the spike was made too high or low.  If trends show multiple incorrect spike amounts, the trainee will need further training.

Opportunities to learn more

If you’re curious to learn more about control charts, the below resources are a good place to start:

Join us for more information

about the environmental laboratory industry, plus events we’re attending and hosting.

New Private Drinking Water COC / Submittal For

We’ve updated our Private Drinking Water COC/Submittal Form for Coliform Bacteria and basic chemical analysis. You can download it at  our Resources page.    

New Sandpoint Drop-off Location

Our Sandpoint drop-off location has moved from Ponderay Pump to Kootenai-Ponderay Sewer District: Kootenai-Ponderay Sewer District511 Whiskey Jack RdSandpoint, ID 83864 Please drop off samples Tuesday afternoons before 5:00 PM, or between 8:30 AM and 8:45 AM on...

PWS Drinking Water COC

We’ve updated our Public Water Supply (PWS) Drinking Water COC/Submittal Form for Coliform Bacteria and basic chemical analysis. You can download it at  our Resources page.    

Biotic Ligand Model

The Biotic Ligand Model (BLM) takes into account many environmental conditions in order to determine if a metal exists in a form or concentration that is toxic to aquatic life.  Toxicity is usually based upon the dosage of whatever it is that we are looking at.  At...

SVL Analytical celebrates 50 years of science, family and mining

From geology exploration to environmental compliance, SVL attributes its longevity to hard work and an adaptive mentality. The laboratory may be an unrecognized partner—that is until something goes wrong like a spill, a breach, a new compliance rule. Our data users...

TCLP or SPLP on a Solid Sample

Why is this TCLP/SPLP on a solid sample a common question? The main reason is that people don’t understand the difference between characterization and hazardous determination.  The EPA developed the TCLP Program to determine when certain materials have to go to a...

What does Cation/Anion Balance Mean?

Introduction to Cation/Anion Balance (CA Balance) Water that is potable (drinkable) should be electrically neutral.  This is determined by taking into account results from the following analytical testing: pH, conductivity, total dissolved solids, and other analytical...

What’s the difference between accuracy and precision?

Have you ever wondered what the difference between accuracy and precision is? The classic example is this: I shoot five arrows from a hundred yards and they land either in or just outside of the bullseye.  The consensus from the gallery will be that I am a very...

How Low Can You Go – Well No Lower Than The MDL

There is always confusion on how low a lab can go when it comes to what their instruments can detect.  The EPA and TNI came together and changed how Method Detection Limits (MDL) are established for an instrument or group of instruments. They wanted to account for the...

Significant Figures Use by Laboratories

What determines the amount of numbers you see on your report? Each test that we do has a level of sensitivity associated with it.  Tests that you can do by visual inspection have the lowest sensitivity and are usually reported in whole numbers in a range of say 1 to...