Calculating effective SSN (sunspot number) I am doing research on SSN-like parameters. As I can see, effective SSN is a parameter that is derived from SSN or other parameters. Do anyone know how to calculate effective SSN?

For example, this file has some parameters. See also this page.
The effective sunspot number $R_{\text{eff}}$ is calculated through a mix of observations and model calculations. It focuses primarily on some parameter called the frequency of the ionosphere F2 layer, denoted $\text{foF2}$, the highest frequency of electromagnetic radiation which can be reflected off the F2 layer; it can be observed as well as computed based on a certain model (real-time observational data from stations around the world is available here). More information on $\text{foF2}$ can be found on this page.

The mean-squared error between the observational value $\text{foF2}_{\text{obs}}$ and the calculated value $\text{foF2}_{\text{calc}}$ over observations by $n$ stations is
$$\Delta=\frac{1}{n}\sum_{i=1}^n\left(\text{foF2}_{\text{obs},i}-\text{foF2}_{\text{calc},i}\right)^2$$
where $_i$ denotes the value at station $i$. $R_\text{eff}$ is defined to be that chosen sunspot number such that $\Delta$ is minimized.

This is just an application of a least squares method to fit a model framework to match observations. An example of this using the Simplified Ionospheric Regional Model (SIRM) is Zolesi et al. (2004), although the procedure for calculating $R_\text{eff}$ was first proposed by Houminer et al. (1993). This was introduced to augment or replace something called the 12-month smoothed sunspot number, $R_{12}$, which is entirely based on observations. Zolesi et al. write


  It is therefore expected that during periods of relative ionospheric quietness, when the observed $\text{foF2}$ value is much closer to the model predicted median values, the $R_{\text{eff}}$ does not differ much from the $R_{12}$. On the contrary, during periods of ionospheric activity, the $R_{\text{eff}}$ should have large difference form [sic] $R_{12}$.