ChemPoint/ChemStat Frequently Asked Questions

Q. Is it LAN compatible?

A. Yes, you can run it from a LAN with the following restrictions:

The LAN must support long file names
For ChemStat and ChemPoint Standard edition, only one user can access a ChemPoint database at a time (no sharing is allowed). ChemPoint Professional does support file sharing.

Q. Does it include all the regulatory methods in the USEPA guidance documents?

A. It includes all methods that are given "significant attention" in the 1989 and 1992 guidance documents and the USEPA Unified Guidance. The following methods are included:

Box/Whiskers plot
Time-series plots
Probability Plot
Shewhart-CUSUM control chart.
Parametric ANOVA with Bonferroni comparison
Parametric, non-parametric, and Poisson prediction limits
Parametric, non-parametric, and Poisson tolerance limits
Confidence interval
Kruskal-Wallis non-parametric
Wilcoxon Rank Sum non-parametric
Levene's Test for equal variance
Bartlett's Test for equal variance
Shapiro-Wilks/Shapiro Francia for Normality
Coefficient of Variation for normality
Skewness
Aitchison's and Cohen's Adjustments

ChemStat also includes many graphs and methods not mentioned in the guidance.

Q. Can you use it to compare data to a set point....ACL, MCL, risk number or concentration limit? Can that be changed per well, per constituent?

A. Yes.

Q. Can I pull up all the data in a spreadsheet format to check for missing data?

A. ChemStat:
Not really in a spreadsheet format. There is a general report that shows all of the data for a selected parameter. The are grouped first by well, and then by sampling date. It is very easy to locate missing data in that report

A. ChemPoint:
It is easy to locate missing data using the data entry program, or the variety of reports that are available.

Q. Can I do an initial check for censored data and outliers?

A. Yes in ChemStat. Dixon's test for outliers, Rosner's test for outliers, and the Discordance Outlier Test are included. You can also automatically exclude outliers.

Q. If there is more than one background well, can the software combine all upgradient wells for background?

A. Yes, it does that by default. However you can also compare each background well individually, but it is more tedious.

Q. Will the software run the statistical method used by the facility/consultant?

A. It can only run the methods it supports. Additionally, there is always a possibility that two different software applications will vary somewhat in how they implement the same statistical method. For example, the 1989 and 1992 guidance docs provide two different implementations of tolerance limits. There are also many variations on how prediction limits are implemented among different statistical programs.

Q. How does the software treat non-detects?

A. With ChemStat, you have the option of replacing them with:

detection limit
DL/2
1
0
Cohen's Adjustment
Aitchison's Adjustment

Q. Will the software tell me if and why the observations don't meet the performance requirements of the statistical method...such as:
a. Too few observations to run an accurate test
b. Too many non-detects
c. If homogeneity of variance is required
d. If normal background data is required
e. If it is required that you start with an uncontaminated well
f. If seasonality of data is present or will effect the performance standard of the statistical method.

A. a and b. Yes, but it let's you proceed anyway
c, d, and e. These requirements are only specified in the documentation, not at the time you run the test
f. No. You must test for seasonality independent of the selected method. ChemStat does includes tests for seasonality

Q. Will the software let you set a numerical standard for comparison (ground water Protection Standard may be background, MCL or ACL (risk number)?

A. Yes. Some statistical methods support this type of comparison.

Q. What happens if all the samples are not concurrent?

A. That does not cause a problem for any test. How this situation affects the test varies depending on the statistical method.

Q. Will the software allow use of 4 independent samples per constituent per well per event?

A. Yes. You have an option to average them and use them as one sample, or use them as four independent samples. Of course four sample from the same well on the same date should not be called statistically independent.

Q. Will the software allow quarterly, semi-annual, annual, monthly or other sampling frequency?

A. Yes, any sampling frequency is allowed.

Q. What transformations of data will the software allow?

A. The following transformations are supported at this time:

Original Data
Natural Logarithm
Log base 10
Square root
Cube root

More will be added as they are requested.

Q. Can I have the software show me all the values for a sampling event that are above detect, above MCL, above a risk based number?

A. Yes. There is a report called a Threshold Report. It shows all analyses above a specified value. ChemPoint also supports some similar reports.

Q. How easily can I develop a time trend? Box plots?

A. Very easily. ChemStat has very capable graphs available with just a menu click. Time trend graphs are available for multiple wells for a single parameter, and multiple parameters for a single well. ChemPoint Professional has even more powerful graphing capabilities to trend plots.

Q. Will the software allow me to compare more than one parameter at a time to see concurrent trends?

A. In ChemStat, the only multiple parameter comparison is Concentration vs. Time plot that plots concentrations from any parameters you select for a single well over time. All other graphs and statistical methods are performed on one parameter at a time, and the calculations are completely independent of any other parameters.

ChemPoint Professional has some graphs that are very useful for comparing concentrations or different parameters.

Q. How does the software require the background data (from previous events) be set up?

A. Background data is set up the same as compliance well data. You can specify which wells are background wells. Using ChemPoint, you can specify a different date range for background data than for compliance well data.

Q. If a well triggers, how easily (quickly) can I go to the next further downgradient well and see if it shows contamination as well?

A. Generally very easy, but it depends on the statistical method. Some methods compare each compliance well individually to background, so the statistical results for each well are displayed on the same "page". For other methods, you would have to open up to windows and compare them side by side, which is easy to do. However the program is not able to determine which the well is the next downgradient well.

Q. Can ChemStat do two-tail analyses for a parameter like pH?

A. Yes, parametric prediction limits, Mann-Kendall test for trend, and Sen's slope estimator are all two-tailed tests available in ChemStat, among others

Q. It appears that the only use for ChemPoint is to generate reports. However, the manuals indicate that you need ChemPoint to translate the data for export into ChemStat. Please clarify.

A. ChemPoint does generate reports, but the more important function is to maintain the validity of your data and too keep all data in a central location. ChemPoint allows you to make sure all parameters have the correct name (no multiple names for the same parameter) and to make sure that you are not missing data or have duplicate data that does not really exist. The importance of maintaining data integrity can not be overemphasized. It is inadvisable to store your data in Excel spreadsheets and convert the spreadsheet data every time you want to perform statistics. It is just too easy to lose data.

Q. If I input data as "<5", the database knows to interpret this as not detected with a detection limit of 5? And then will calculate statistics based on 1/2 of the detection limit for this value?

A. Yes, but you have to tell it to do so. I assume you are using the Universal Importer in ChemPoint to convert your data. In that case, you have to tell the Universal Importer that non-detects are indicated by the presence of a "<" symbol. After the data are in ChemStat, you can specify whether you want to represent non-detects by 0, 1, 1/2 DL, or DL.

Q. For parameters such as specific conductivity and pH, units are not in ppm or ppb. I assume that units such as umhos/cm or pH standard units are identifiable by the database?

A. Yes. ChemStat converts all values to ppb if that is appropriate (if that option is selected). Standard units for pH and umhos/cm do not convert to ppb, so they are not converted. ChemPoint has more extensive unit conversion support. In ChemPoint, you can add custom units and specify conversion factors.

Q. Why should I have ChemStat convert all values to ppb?

A. It is possible to import data without converting to parts-per-billion, but the conversion is recommended. All statistical comparisons must be with consistent units. ppb was chosen because it is commonly used and it is rare to have detected values below 1 ppb. It is important that your statistical data all be 0 or greater than 1. Otherwise, log transformations produce negative numbers. ChemStat will still work with values less than 1, but you must be careful taking the log of such values.

Q. If the detection limits between different sets of data are varying, does the database set the detection limit as one value, or does it vary with the sample data set?

A. The detection limit is always the value specified for a particular analysis. If the reported detection limits vary, that is how they will appear in the database.

Q. When setting up new sampling events, and/or parameter groups in ChemPoint 4.0, how are replicates handled? Can they be added to a parameter group, or must each replicate be dragged and dropped to a sample location or container individually? I've tried adding them to a parameter group, but when the file is exported to ChemStat and an analysis conducted, some replicates are excluded from the test. For example, the test would include replicates designated with the "a" code but would ignore the "b", "c", and "d" coded replicates.

A. Replicates can be added to a parameter group and then added to the container as part of the group. Be careful when importing replicates into ChemStat. There is an option to average all parameter concentrations for the same date. Make sure that option is not selected (although statistically, you should not consider replicates as independent samples). You should be able to create replicates in ChemPoint and have them maintain their "replicate status" in ChemStat.

Q. Is is correct to assume that if the data for a certain well/parameter is log-normally distributed, then the data must be kept in its logarithmic form for all other tests?

A. Yes, but only for parametric tests. You can have data that is not log-normal, and do a non-parametric test on it because normality is not required.

But the one-word answer to your question is yes.

Q. Is there a way to delete a sample date (and all analyses on that date) or delete a single sample (container) and/or parameter for a sampling event? We have a sample date previous to Subtitle D and the State wants us to remove the data. In addition we had a mistake in entering and have several parameters that we need to delete (i.e. pH, versus pH, field) and some dissolved metals data that the State wants removed from the database.

A. Yes, you can delete an entire sampling date and all data for that date, but it is not recommended. There are other ways to exclude the data from a statistical analysis or graph.

Q. Is there a way to reorder the parameter list to another order (e.g. according to Appendix I parameter number)?

A. Yes. Go to the Facility Parameter View in ChemPoint. Drag and drop the parameters so that they are in the desired order. The select Reorder from the Data menu. That will reorder all of the parameters to the new order both for data entry and for reports.

Q. I tried importing some data for a single well into ChemStat and I get a results report but no data seems to be available for the graphing component. I have also attached this file from ChemStat.

A. The problem is that you did not specify the well gradients. You need to specify well gradients in ChemStat by selecting Change Well Gradients from the Options menu. Only data from wells that are listed as up-gradient or down-gradient will be graphed. Data from wells classified as "unused" are not graphed.