In the first part of this blog article we became familiar with the RSS and started to get an insight about the influence of the individual data values. This is followed by this part.

Hat Values and Cook’s Distance – what is really influencing the regression line?

So far, we were thinking about the influence of data points, but have actually not clarified what influence actually means. One intuitive way to think about that is to consider what would happen to the regression line if a single data point would be removed from the data set. If one data point has a big influence on the regression line, then, removing that data point should change the regression line a lot, which can be measured by a difference in the slope and/or y-intercept. This can be done and is shown in the following Figure 1:

Often, the small things make the biggest difference in life. Sometimes these things we do not recognize at first as big but as soon as we draw our attention to them, they become more important.

In analytical method validation, one of these small things is the so-called sum of squares or residual sum of squares (RSS). The (residual) sum of squares you will often find as a number in validation reports that, at first sight, might be of no interest at all. That is why, in this article, we will explain in more detail what this number actually means and why it is of importance. We will discuss its meaning and its importance, as well as the pros and cons and what can be done to avoid statistical pitfalls when using the RSS.

In this blog article the influence of filter integrity test parameters on bacterial retention will be discussed.

Sterile filters can be used during the manufacture of parenteralia for example. If the product is is a protein solution two filtration steps are required for aseptic preparation. First a bioburden reduction filtration and directly before filling a sterile filtration.

Microbiological methods are used in many applications in the pharmaceutical industry. Since it involves working with living organisms, various factors must be considered during an ongoing experiment. Many traditional methods have been established over the years and are listed universal methods in the pharmacopoeias. Considering the given requirements in the instruction their application doesn’t need a validation, only a verification is sufficient. Due to recent technological advancements, it is possible to use alternative methods developed by the laboratory or a company itself. To ensure the new method also demonstrably leads to correct results, a previous validation is must.