GolfCabal Handicaps
Handicaps are a standard part of golf, and are completely covered by USGA rules. This document will discuss the way USGA calculates handicaps, the philosophy behind it, and how GolfCabal handicaps will necessarily differ from the USGA method. My own theory of golf simulation handicapping will leak through, and that is good, because it will help you understand both the existing USGA-like system, and the new, more relevant system we will soon to begin to pilot.
Roger Davis
The Basics
The handicap, in its most primitive form, would be the average over (or under) par that a golfer scores. If Shivas averages 8 over par, and Hunter averages 10 over par, then Shivas is going to give Hunter 2 strokes per round advantage, the difference between their handicaps. The USGA formula is more complex than this simple plan, but works out to very nearly the same number, mathematically, as you will see. The differences came to exist for three main reasons:

1) This scheme allows a player to cheat the system by intentionally scoring high in some rounds, thus padding the handicap, or even by purposely scoring exhorbitant scores on the last few holes of each round, after the bets have been settled.

2) The simple plan of using the average over par is accurate only if the players have established their averages on the same course, or the same set of courses in the same proportion.

3) A better scheme is necessary so that the superior player retains a small but definite advantage. "You dont get full credit for how bad you are" is an objective that is behind all the innovations in the USGA handicap method.
The Formula, How it Differs from Simple Average
In the USGA plan, you dont count all the rounds. Only the 10 best of the last 20 are averaged. A potential sandbagger is not likely to spend half his golfing days shooting intentionally bad scores.

Equitable Stroke Control (ESC) prevents a player from benefitting by shooting 12's on the last few holes, by providing that before submitting a round for handicap, a player changes all higher scores to "7". (This "7" rule is almost accurate, but the max score per hole varies a bit according to handicap.)

The par on particular holes, and thus particular courses, varies from the norm, so an adjusted "par" called Course Rating is established to normalize scores shot at different courses. Course rating is based more upon distances than difficulty, although both attributes are considered.

The latest equilizer that the USGA added to the scheme is Slope Rating, whose purpose is to factor in how severely the particular course penalizes the inferior golfer.
Equitable Stroke Control
When you come to the clubhouse with your completed scorecard, the first thing you must do is get rid of "blow up" holes. Earlier I said "No score can be higher than 7." This is actually true only if your handicap is between 10 and 17, but...that's where most of us live. For those of you in other ranges, here is a chart from USGA. I'm a 13, so if I shoot an 8 or a 9 or a 10 on a hole, I change it to "7" on the card. AFTER I settle my bets, that is. But before I report the round to the handicapper.

The Course Rating
The next USGA adjustment is to use an "adjusted par" or Course Rating to normalize the differences between various courses. Baynes Creek GC is very short, with par 4's ranging from 285 to 370, and only 3 par 5's on the course. The par is 71, but the Course Rating is 66. If I shoot 83 at Baynes Creek, I subtract 66 from 83, and my Handicap Differential for the round is 17. I shot 12 over par, but it is the course Rating that matters. Par doesnt enter into it.
The Slope Rating
You will recall that at Baynes Creek, while the par is 71, the course rating is only 66, and that this difference is based mainly upon Course Rating. On the other hand, this course has a lot of trouble. The difficulty is reflected mostly on the back nine, where the holes are very narrow, and, while there is plenty of good fishing, there was not really enough land to build a course. You are crossing creeks and ponds, or playing alongside of them on every hole, and you have lots of trees to deal with as well.
The USGA realized there was a need to begin reflecting into the handicap the relative difficulty of courses. We will soon discuss how the USGA determines the Slope Rating, but first, let's see how the Slope Rating is used in handicapping.
Adjusting the Differential
So far, we have adjusted our 84 at Baynes Creek by changing an 8 to a 7, bringing the score to 83. Then we subtracted the Course Rating of 66, giving a Differential of 17.

Now is the time we apply the Slope Rating, and here is how: You multiply the Differential by 113, then divide the result by the Slope Rating.

Baynes Creek has been assigned a Slope Rating of 118 (indicating it is above average in difficulty).
In the present case, we saw that a 17 Differential went down to 14.8. This means that even though we shot 17 over, it is being reckoned as if it was 14.8 over, because it is an above-average difficulty course. I know, it sounds like Form 1040. Basically all you are doing is multiplying by a difficulty factor.
Here is a chart that shows the sense of the Difficulty Factor:
The Factor INCREASES the Handicap Differential on easy courses, and DECREASES the Differential on difficult courses. This is because shooting +10 over at a tough course is like shooting +5 over at an easy is an equally tough accomplishment.
Likewise, when you shoot +5 on that easy course, the Factor will be more than 1, and when you multiply it by the actual differential you shot, the result will reflect the difficulty of the course.
At the end of each round, you calculate your Differential as detailed above, and you keep a journal, noting all details of calculation, and including the date of the round.

When you are ready to calculate your handicap, your first select your last 20 rounds, and discard the others to history.

Now, sort those 20 rounds by the Differential. Keep the rounds with the 10 lowest differentials, and throw out the 10 rounds with highest differentials. You do not get credit for your worst rounds, only your best.

Take the average of those 10 lowest rounds. Do not round off, always simply lose all digits to the right of the tenths place. Always err in favor of a lower handicap.

Finally, multiply that average by .96

Why? Because still again, you do not get full credit for how bad your are. While we are trying to level the playing field, no factor can ever be allowed to disadvantage the better golfer.
Back to the Question: Where does that Slope Rating come from?
There are two theoretical characters who are considered in investigating the Slope Rating of a course: The Scratch Golfer, and the Bogie Golfer.

The Scratch Golfer can hit driver an average of 250 yards, and has the distance to reach a 470-yard green in two shots. He will usually score in the neighborhood of par.

The Bogie Golfer can hit driver an average of 200 yards, and has the distance to reach a 370-yard green in two shots. He will usually score about 18 over par.

The definitions of these two ideal golfers will hold true on courses of moderate difficulty, but on very easy courses, the difference between their scores will be smaller. The Scratch Golfer may win by only 15 or 12 or less on the easier courses. (Picture a course where each hole is only 2 feet in length. This is the world's easiest course, and certainly the Bogie Golfer will not need any handicap strokes at all.) On the more difficult courses, the differential between the two golfers can increase to far more than the usual 18 strokes.

When the USGA set out to level out the differences in difficulty between courses, the first thing they did was to draw some graphs:
As the chart shows, the Bogie Golfer's score suffers more than the Scratch Golfer's, as they move to progressively more difficult courses. The green line shows the Difference between their scores. And the SLOPE of the green line reflects the extra impact on the bogie golfer's score. The tougher the course, the steeper the slope.

The slope of that line, once determined by the observation of tens of thousands of actual rounds of golf, is normalized to 113 (why not 100? I believe the USGA did not want to stigmatize courses that are a little easier than average...they are still above 100.)

A Slope Handicap does not give the golfer an absolute handicap. It provides an Index, which references the Slope Rating of a course in order to determine your Course Handicap at that venue. Your handicap will be higher on more difficult courses, and lower on easier courses.
Checking your work: The one mistake you can make is getting the Factor "upside-down"..."Is it Slope-over-113, or 113-over Slope?" you ask yourself. In this instance, the Course Rating of 125 is higher than 113, so it is a more difficult course. I expect my handicap to go UP. And, from 12 index to 13 Course Handicap, it indeed went up.

It is fair to mention that you dont need to take a calculator to the course. All USGA-approved courses post a chart that correlates your Handicap index to your Course Handicap. But arent you happier now that you know how to produce the chart?
How GolfCabal Handicaps will Differ
The initial GolfCabal handicap method will be as strictly according to USGA rules as possible. Still, there is one USGA adjustment that will not be possible. Equitable Stroke Control will not be employed. The game itself does not make the adjustment, and GolfCabal does not currently record scores by the hole. However, because of the practical reality of the scores we shoot, it is hardly relevant. We do not often score more than 7 on a hole.

But there is another point of view to be considered: The ESC chart above reflects a formula, but it does not tell the whole story when it comes to the handicaps that we earn playing Links golf. Extending this formula to a handicap of -10, the maximum score per hole would be par!

A much deeper problem exists with very low scores. The top PGA Pro golfers IRL, Tiger Woods, Vijay Singh, Phil Mickelson...those guys have NEGATIVE handicaps. Meaning, they subtract a NEGATIVE number from their gross score, to get their net score, in effect ADDING strokes. I can imagine playing vs Tiger at Baynes Creek: I would subtract strokes from my score, he would add strokes to his. Even so, I would need 3 gotchas and 5 wedgies to have a chance.

I'm sorry for digressing. The point is, if a golfer has a handicap that is slightly negative, like -1 or -2, the system still works reasonably well. But at GolfCabal we are going to have handicaps of -9 and even lower. And the problem that arises is this: Remember our theoretical Scratch Golfer and Bogie Golfer? Well, nice guys that they are, they are completely irrelevant to Links golf. Excuse me, their RELATIONSHIP is irrelevant. The Scratch Golfer still matters, but now he is the INFERIOR golfer. For Slope Ratings to be truly pertinent in Links golf, they would relate the performance of the Scratch Golfer to the Stellar Golfer, or the MesoMorph Golfer. And that, on a Links course, with Links yardages at issue.

Equally troubling is that we currently use the Course Rating and the Slope Rating of the IRL Prototype courses in calculating our handicaps, and there is no assurance that IRL difficulty tracks at all with sim difficulty. Considering a pair of courses, the one that is easier IRL might be more difficult in Links.

The reason for the "best 10 of the last 20 rounds"...the reason it is 20 rounds and not 4 or 8, is because the handicap should reflect average performance over a long period of time. The USGA actually offers smaller versions of the same scheme, and this is the other USGA schema that GolfCabal has opted out of, because we play far more rounds than the outdoor golfers do. In the best years of my life, I played golf 3 times per week, usually shooting about 72 holes. Most GolfCabal golfers play 8 rounds or more in an off week! GolfCabal will not begin handicapping a golfer until he has played at least 20 rounds, and handicaps will not be re-calculated during a tournament. New handicaps are calculated once per week, and the same handicap will apply to all four rounds of a player's tournament.

We are initially using a very compliant USGA system of handicapping, but at the same time we will be tracking our actual performance on all courses, including APCD original courses for which there is no IRL prototype. We will also collect scores from other web sim sites, and we will include course conditions into our calculations, to judge their impact. This additional information will prove to be of increasing interest as the database growths through time, and will help us all discover where our games need the most work. Gathering this info will finally allow us to calculate Course Ratings and Slope Ratings that will truly level the playing field by offering a handicapping structure that is far more pertinent to Links golfers. Did you ever notice that when USGA handicaps are used in Links, the winning handicap score is often well over par? Did you ever notice that the better players tend to win handicap events rarely or not at all? These are strong indicators that the handicaps systems that have been used are not accurate.

To repeat: The handicap system currently in place on The Golf Connection is a strongly USGA-like engine, and it utilizes the Course Rating and Slope Rating of the IRL Prototype courses. Later, we will begin to also display net scoring results of an exciting new handicap system more pertinent than USGA to computer simulation golf.