Impact Index, unlike every other cricket statistical system in the world, is completely transparent in its workings. It is possible to do all these calculations manually too, at the back of an envelope, once the system is understood. However, to save time and energy, we have automated the entire system and are in the process of running all cricket data through it.
A simplified step-by-step list of its mechanism is given below, in case you want to understand how it really works. This methodology is for limited over matches.
1) Based on the innings totals, a base figure is generated for the match. This is measured in runs, for all players (batsmen and bowlers and wicket-keepers).
2) Every performance in the match is thereafter measured against this base figure (as a ratio). One IMPACT point is procured when the performance is equal to the base. That is seen as merely the par performance for the match.
3) For a batsman, IMPACT points are garnered for a) Runs Tally b) Strike Rate c) Pressure d) Chasing and staying not out in the second innings. e) Partnership-Building.
4) The Strike Rate IMPACT can go into negative or positive depending on his strike rate vis-à-vis the base strike rate in the match.
5) The Pressure IMPACT only measures pressure that comes from fall of wickets. It kicks in when a batsman comes in to bat in a tough situation (as defined from how many wickets have fallen) and crosses the base runs. Tough situations are defined as per the base runs.
6) For a bowler, IMPACT points are garnered for
a) Wickets (the top 8 wickets and the last 3 have different values, in most cases, as per the circumstances of the match)
b) the Economy Rate (again, calculated against the base economy rate of the match - in T20 matches, the economy rate has a slightly higher value, as per the circumstances of the match)
c) Breaking Partnerships (its limit is set by using a multiple of the base) d) Building Pressure (taking quick wickets within the base).
7) Catches, stumpings and credited run-outs all get extra IMPACT points (a fraction of the base). The winning captain also gets an addition to his IMPACT (again, a fraction of the base). Wicket-keepers get flat points for doing an assigned job.
8) All the above points are measured against the base figure, and are therefore ratios of the base in some way (which is fundamentally why they are measurements and not ratings).
9) For Strength of Opposition - all teams in all matches are graded in categories of A, B or C in terms of team strength (with A being the strongest). The break-up is done in a scientific manner, using previous series as a pointer, and also the result of that series.
10) For Series/Tournament Defining performances - the highest-valued single component in this system rewards outstanding performances in critical circumstances for a team within a tournament or a series context – all chosen completely objectively, with no scope for subjective interpretations.
11) In a career context, the figures from all heads are tallied. All numbers are necessarily between 0 and 5, up to two decimal points.