Zetasizer Advance Averages
Averaging measurements is a useful feature when reporting results from multiple repeats or even comparing different datasets from similar measurements. You can quickly calculate the overall result for your measurements and directly include this in your reports. However, you need to consider how this averaging is performed for efficient reporting of your results.
Which results can I average?
The ZS Xplorer can now create average records for the following measurement types:
Simply select the records you would like to average and click the Create Average Result button at the top of the Record Selector:
Alternatively, you can also select multiple records, right-click and select create average result.
This creates a new record where the software averages the measurement data rather than just the numerical values. This may sound like a subtle difference, but results may change slightly depending on what values you are analyzing. Firstly, it is important to consider the averaging process for each method:
- Single-angle size measurements – the software averages the correlograms and re-applies Cumulants and Distribution analyses to the new record, to recalculate Z-average, PI, and peak positions, areas and widths.
- MADLS® measurements – the individual angle correlograms are averaged. The software then applies the MADLS algorithm.
- Particle concentration – The MADLS averaged result is re-processed for concentration.
- Zeta potential measurements – the software averages the phase plots and frequency distributions for each record and reprocesses the resulting Fast Field and Slow Field parts of the measurement to calculate the mean zeta potential and zeta potential distribution, respectively.
Statistical vs Measurement Average – why do we see a difference?
The simplest way to calculate an average is arithmetic. Add all the individual measurement results together then divide by how many there are. For example, the statistics table will calculate the arithmetic mean of the displayed parameters.
When you select multiple records, the values displayed in the statistic table are the arithmetic averages for the final results. Therefore, because the software averages the “raw data” when creating an average measurement, it could lead to small discrepancies in the results.
These are size results for a black ink sample obtained on a low-volume capillary cuvette. The top row results show 5 repeats of the same measurement and b) the averaged measurement for those repeats. By reprocessing the average measurement, we get an average result that is more appropriate for comparing different types of data.
Additionally, an important benefit from creating average records is that this may lead to an improvement in data quality.
In the example above, the gradients in the phase plots are much clearer and better defined which should lead to lower batch-batch variability.
Why can I not average some of my records?
Each measurement type above follows certain criteria that determine whether it is possible to average measurement. For all measurement types, certain measurement settings and parameters have to either be the same or within a certain range. Otherwise, the software disables the Create Average Result button displays an error message “Invalid selection to create average result”.
For instance, it is not possible to average size measurements in different cells, at different temperatures or using different analysis models – as this would likely compromise the validity of the results. Similarly, it is not possible to create averages of zeta potential measurements if the software configures different drive modes (constant voltage or current) or attenuator positions during the optimization stage.*
*The criteria mentioned are only examples and others will also be applicable depending on the measurement type.
Previously on Material Talks
- Standard deviation in size data – Stdev.S ?
- Help for my instrument – one step away
- Zetasizer Advance in bullet points
Further reading