XLSTAT: Sensory shelf life analysis in Excel

 

Dataset for Example

The data used corresponds to the evaluation of a fresh fruit juice by 19 assessors at different times. The juices have been tested 6 times at day 1, 2, 3, 4, 5 and 6. The assessors have given their liking (yes/no) for all these times. In the data, the assessors' evaluations are coded using 0 when the evaluation is negative and 1 when it is positive.

Here is the data format:

You can change the value (0/1) to any other value in XLSTAT (yes/no for example).

 

Goal of this analysis

The goal of this analysis is to visualize the best period to put a product in a shelf for selling it. Parametric survival models are used to model the time at which an event occurs.

 

Setting Up

• Open XLSTAT.

• Click on the Sensory/ Time data analysis menu and select the Sensory shelf life analysis feature.

• Once you have clicked on the button, the dialog box appears.

In the General tab:

• Select the assessor x date table as presented above and a column with the value associated to each date in the time data box. We use the Weibull distribution to fit the model.

• Other options are left with their default values.

• Click on the OK button to launch the computations.

• The results are displayed on a new Excel sheet.

 

Interpreting the Results

The first table corresponds to basic summary statistics associated to the time data. A graphic is also displayed giving an overview of the answers of the assessors.

 

This plot shows a decrease in the number of assessors that appreciate the orange juice. At the end of the analysis, only 4 assessors still like the product.

The tables displayed afterward are similar to those displayed in a parametric survival curve. A Weibull curve is fitted to the model. We can see that both parameters are significant.

The preference distribution function plot based on a Weibull distribution is as follows:

Finally, the quantiles are obtained and are very useful for decision making.

We can see that median time is between 4 and 5 days after the product has been put on the shelf.

Many more analysis and decisions can be taken with sensory shelf. Explanatory variables associated to each assessor can be added.