Rating FIFA 'A' matches is somewhat more challenging than rating national professional leagues. League play is typically a well balanced design with a small number of teams, each playing all others twice, home and away. Every game counts towards the league standings.
The collection of international matches is highly unbalanced, with little contact between some regions. Some teams go for extended periods without playing a match at all, while others schedule numerous matches.
International matches come in several categories: friendlies, friendly tournaments, continental qualifiers, continental championships, World Cup qualifiers, and finally, World Cup matches. These matches are taken more or less seriously, and leading to variation in the quality of the teams fielded by a country. Thus it is important to weight the matches. I am studying the proper weighting scheme, but at present have only two levels, with all types of `friendly' matches getting 2/3 the weight of the `serious' matches. This will no doubt change at some point, but based on estimation of the over-dispersion (excess variability) of friendly matches, it seems like a reasonable value.
The model used represents the log of the odds for the home team in terms of the difference of the ratings. A difference of 100 rating points corresponds to 2:1 odds, or a winning probability of 2/3. The absolute value of the ratings is not important, only the differences between ratings. For more details, see my ratings system description, which is unfortunately not quite up to date. You should complain to the author directly.
There are also terms representing the home field advantage ( currently worth about 130 rating points for men's teams, and 60 points for women's teams) and the probability of a tie. I'll be happy to provide details on request.
Here is a small table showing the predicted probabilities of wins, losses, and ties, for various rating differences, based on men's results. It assumes that the match is played on a neutral site (else add home field points to the home team rating).
Rating Probability of
Difference Win Loss Tie
0 .31 .31 .38
100 .48 .19 .33
200 .65 .10 .25
300 .79 .05 .16
400 .88 .03 .09
500 .94 .01 .05
This assumes that the home field advantage and the
tendency to tie matches is constant across
teams, which is probably not correct. However, it should be
about right on the average.
I extracted the data form the RSSSF archive of International results maintained by Ron Kessler ; and Russell Gerrard's RSSSF searchable Archive of (men's) International Football Results.
You may wish to compare these ratings to
FIFA's national team ratings.
FIFA also maintains a list of
International A matches.