Slope ratings

[spidey]

Dunno if this is the right place to post this question, but....

What does a Slope rating sheet look like. I'm curious to know what is rated and how it's rated in coming up with a slope for a course.

I guess my ulterior motive is to second-guess the slopes of various courses, but it just seems that some of the tracks around town seem to be easier, or harder than their slopes would suggest.

spidey

[Gary Hill]

Under the slope system, courses are rated according to the relative difficulty for both the scratch player and the bogey player. The system takes into account all factors that affect the playing of the course. The course rating team is composed of at least three trained and experiences persons determined by the provincial association's course review committee. The team must be apprised of any unusual local conditions. The team leader must be a graduate of an R.C.G.A. course rating seminar. Each team member will evaluate every obstacle on the course on a scale from 1 to 10 and the team shall reach a consensus on the obstacle rating. The rating file will be sent to the provincial association for future reference including the names of the team members, a scorecard, information regarding weather, availability of a fairway watering system, conditions of the day, and a certificate verifying the accuracy of the course measurements.

Measurement of the holes shall be done on a horizonal plane from the starting point (which shall be permanently marked) midway, back to front, of the teeing area to be used, for each set of markers, to the center of the green for each hole. In the case of a dogleg hole, measurement shall be along the center line of the fairway to the axis and then to the center of the green.

Effective playing length is obtained from official measurements of the course and an evaluation of the factors which cause the course to play significantly longer or shorter than its measured length. Yardage ratings for both scratch and bogey golfers are determined by applying the effective playing length to the yardage rating formulas. Course rating is the scratch yardage rating of a course modified by the obstacle factors as they affect a scratch player. Bogey rating is the bogey yardage rating of a course modified by the obstacle factors as they affect the bogey player. Slope rating is the difference between the bogey rating and the scratch rating multiplied by 5.381 for men and by 4.24 for women.

The effect of obstacles is converted to yardage which is added to or subtracted from the measured length to yield the effective playing length. Effective playing length, in turn, is applied to the yardage rating formula to produce scratch and bogey yardage ratings. Other general factors will be factored in such as elevation, doglegs, prevailing winds, abnormal roll, and altitude above sea level. Each hole will be rated for obstacles on a scale from 1 to 10 and considered separately for scratch and bogey golfers. When the rating process has been completed, units for each factor are totalled and multiplied by a relative weight factor.

The following 10 obstacles rated shall be rated on a scale from one to ten by each team member.

Topography - Difficulty of stance in the landing area and the vertical angle of the shot from the landing area to the green
Fairway - The effective width and depth of the landing area, which can be reduced by a dogleg, trees, or fairway slope.
Recoverability and Rough - The existence of rough and other penalizing factors in the proximity of the landing area and around the green.
Out of Bounds/Extreme Rough - The existence of out of bounds in the proximity of the landing area and around the green: extreme rough which is similar in effect to out of bounds.
Water Hazards - The existence of water hazards near the landing area and around the green.
Trees - The strategic location, size, height and number of trees.
Bunkers - The existence of bunkers in the proximity of the landing area and around the green.
Green Target - The size, firmness, shape and slope of a green in relation to the normal length of the approach shot.
Green Surface - The contour and normal speed of the putting surface.
Psychological - The mental affect of play created by the proximity of obstacles to a target area.

The scratch yardage rating for men will equal the effective playing length of the course plus 40.9 divided by 220.
The bogey yardage rating for men will equal the effective playing length of the course plus 50.7 divided by 160.
The scratch yardage rating for women will equal the effective playing length of the course plus 40.1 divided by 180.
The bogey yardage rating for women will equal the effective playing length of the course plus 51.3 divided by 160.

The course rating will equal the scratch yardage rating plus the scratch obstacle stroke value.
The bogey course rating will equal the bogey yardage rating plus the bogey obstacle stroke value.

The slope rating for men will equal 5.381 times the difference between the bogey course rating and the scratch course rating.
The slope rating for women will equal 4.24 times the difference between the bogey course rating and the scratch course rating.

This should be all the information you need to second guess the slope rating.

[spidey]

but thanks anyway, much appreciated.

spidey :

[Dutchie]

As I am a bit of a number nut, I have done some serious spreadsheet work on course ratings and slopes of local courses.

First of all, the course ratings...

I calculated scratch yardage ratings for a number of local courses, and to my surprise these numbers were without exception within one point of the course rating. In other words, the so called scratch obstacle stroke value seems to be pretty insignificant for Ottawa courses, as it is less than one, compared to an average rating of about 68 of the white tees for most courses.
To my even greater surprise, often the scratch yardage rating was higher than the course rating, which means a negative value for the obstacles. To me that seems to be impossible according to the rules?

Then the slope ratings...

I used these to calculate bogey course ratings, and compared these with calculated bogey yardage ratings. Now the spread is larger, the difference between the two being between -2 and +4. Again we see negative values, and on average not much difference between the official rating and a rating calculated from yardages.

This begs the question: are courses around Ottawa rated at all, or do they just do a calcution based on yardage?


By the way, based on its length, the new longish Falcon Ridge 9-hole course will have a course rating of 37.3 and a slope of 127, so don't worry if you shoot 5 shots over your average

[Gary Hill]

I calculated scratch yardage ratings for a number of local courses

It is impossible for you to calculate the scratch yardage ratings for a golf course.

I think you have failed to differentiate between measured yardage and EFFECTIVE playing length.

The effects of obstacles (see earlier post) are converted to yardage and then added or subtracted to the ACTUAL yardage to give EFFECTIVE playing length of the hole.

Your failure to use EFFECTIVE playing length has virtually guaranteed the calculated similarity between the official rating and the rating from calculated yardage.

BTW - Falcon Ridge has not been rated and any associated numbers are purely speculative.

[Dutchie]

Thanks for your reply Gary.

I agree I failed to differentiate between effective playing length and actual yardage. Looking back at the USGA website about course rating (http://www.usga.org/handicap/CourseRating.html) I found that:

The effective playing length (...) is derived by adding the measured yardage of the course to any adjustments made for elevation, roll, forced lay-ups, wind, and altitude.

The obstacle stroke value is a numerical evaluation of all obstacles (topography, fairway, green target, recovery and rough, bunkers, out of bounds, water, trees, green surface, and psychology) on the golf course.

So it seems that your remark that "the effects of obstacles are converted to yardage and then added or subtracted to the ACTUAL yardage to give EFFECTIVE playing length of the hole" is inaccurate.

Anyway, it is still a fact that there is little difference between the actual course rating and slope, and the one calculated from the measured yardage of the course. This means that the effective playing length of courses around Ottawa is very close to their actual yardage and that the obstacle stroke value is usually insignificant.

In short: the course rating is for 98% determined by its ACTUAL length. That really surprises me.

BTW - Falcon Ridge has not been rated and any associated numbers are purely speculative.

Of course, but based on the above I bet my estimate will be pretty close!

[Gary Hill]

I agree that "of obstacles" was erroneously inserted into the statement instead of listing roll, elevation, dogleg, prevailing wind, and altitude separately from topography, fairway, recoveryability and rough, out of bounds/extreme rough, water hazards, trees, bunkers, green target, green surface, and psychological.

Anyway, it is still a fact that there is little difference between the actual course rating and slope, and the one calculated from the measured yardage of the course.

Could you explain what you mean by "the one calculated from the measured yardage". I am unaware of any rating calculated on measured yardage alone.

More explanation may not convince you that "rating" is much more than "yardage", but I will try once more.

The scratch yardage rating is derived AFTER determining the effective playing length.
The separate bogey yardage rating is derived AFTER determining the effective playing length.

An evaluation is made on each hole to determine a Scratch Obstacle Stroke Value.
A separate evaluation is made on each hole to determine a Bogey Obstacle Stroke Value.

Course Rating is the Scratch Yardage Rating PLUS/MINUS the Scratch Obstacle Stroke Value.
Bogey Course Rating is the Bogey Yardage Rating PLUS/MINUS the Bogey Obstacle Stroke Value.

Slope Rating (for men) is 5.381 times the difference between the Bogey Course Rating and the Scratch Course Rating.

In short: the course rating is for 98% determined by its ACTUAL length.

It would be equally accurate/inaccurate to say that course rating is for 98% determined by its ACTUAL par.

This means that the effective playing length of courses around Ottawa is very close to their actual yardage and that the obstacle stroke value is usually insignificant.

I am unaware of any public disclosure of effective playing length by the R.C.G.A. and no relationship to actual yardage can be made without it.

Champlain Golf Course (Blue tees) is 6180 yards with a course rating of 68 and a slope of 118.
Royal Ottawa Golf Couse (Regular Tees) is 6179 yards with a course rating of 70.1 and a slope of 127.

I do not consider such a difference insignificant. The difference in measured length is only one yard and the only other variables in the rating calculations are effective playing length and obstacle stroke value.

Of course, but based on the above I bet my estimate will be pretty close!

I decline to accept the bet. It would be presumptuous of me to guess at a course/slope rating (although seeing that it is a Par 38, it might fit nicely into my new theory of ratings based on par).

[Dutchie]

First of all, let it be clear I do not intend to say that I think it is possible to calculate rating/slope just from the yardage. I do understand how the rating system works, all I am interested in is how large the influence of so-called 'effective playing length' and 'obstacle stroke value' is.

Could you explain what you mean by "the one calculated from the measured yardage". I am unaware of any rating calculated on measured yardage alone.

So this is what I did. I took the ACTUAL (measured) yardage found on the scorecards of sixteen golf courses around Ottawa, and used this value in the formula used the calculate scratch yardage rating (I know that this formula actually uses effective playing length, but I don't have that information. It doesn't matter anyway, because I want to know the influence of actual yardage on the ratings. In other words: let's assume for now that actual yardage = effective yardage, and if it is very different we'll find out from the results).

For example: Stonebridge Sapphire, 6105 yards. 6105 / 220 + 40.9 = 68.7. The course rating is 68.8. So that's very close.

The slope formula is a bit more complex. First calculate bogey yardage rating (6105 / 160 + 50.7 = 88.9), and then the slope ( 88.9 - 68.7 ) x 5.381 = 109. The actual slope is 129, so that's quite a bit higher than calculated. Obviously, that's the effect of the difference between effective playing length and actual yardage, and of obstacle stroke value.

I did this calculation for 16 courses around Ottawa with in total 37 different tees. The difference between average course rating and the average based on actual yardage is only 0.04! Both are 69.0. The maximum difference between the two values is -1.1 (Meadows N-W white tees) and +1.1 (Royal Ottawa regular tees). Two-thirds of the values are within 1 rating points. So the combined effect of effective playing length and obstacle strokes for the scratch player is +/- 1 rating point for ANY course around Ottawa, compared to on average 69 points. Less than I'd expected (those guys are good!).

Then the slope. Slopes purely based on actual yardage are almost all less than the actual slope rating. The average difference is 10.3 points. Apparently, the combined effect of effective playing length and obstacle strokes for the is larger for the bogey player than for scratch player. Also, the spread is larger, varying from -3 to + 20 for the difference in actual slope and one calculated from actual yardage. Most courses fall between +10 and +15, however.

In a sense, it is possible to make a ranking of course difficulty corrected for its actual yardage by taking the difference between actual slope and 'yardage slope' (assuming we're all bogey players!).

Five most 'difficult':
Stonebridge +19.7
Royal Ottawa +18.0
Eagle Creek +15.2
Emerald Links +14.8
Le Dome +14.5

Four most 'easy':
Cloverdale -2.5
The Meadows +3.0
Glen Mar +6.2
Champlain +8.3

So this should be an indication of the amount of obstacles etc. It seems about right, based on my experience of these courses. The rating system survived (sorry Spidey - see top of page)!

Once again, there's no official value to all the numbers above, I just compared the actual yardage of a course with it's rating and slope. Still, the actual yardage predicts course rating within 1 point and slope within 5 points for two-thirds of the courses. From this we can learn that for most courses the effect of obstacles, elevation etc. are similar, with a few exceptions listed above.

Champlain Golf Course (Blue tees) is 6180 yards with a course rating of 68 and a slope of 118.
Royal Ottawa Golf Couse (Regular Tees) is 6179 yards with a course rating of 70.1 and a slope of 127.

It is funny that you mention it. Champlain is the ONLY course that has the same rating of 68 for both the blue and white tees. For ALL other courses, the difference between tees is what can be expected based on their yardage. To me it seems Champlain blue rating should be more around 69. Play the white tees if you want to lower your handicap

...although seeing that it is a Par 38, it might fit nicely into my new theory of ratings based on par

Can you elaborate on that?

[Gary Hill]

For example: Stonebridge Sapphire, 6105 yards. 6105 / 220 + 40.9 = 68.7. The course rating is 68.8. So that's very close.

You have a fatal flaw in your theory. Scratch Yardage Rating is NOT Course Rating.

There are two variables (effective playing length & obstacle stroke value) in the course rating. Since neither of these variables is made public, no amount of backwards calculation from the results will determine either of them. On courses of similar length, one course may have a higher effective playing length and a lower obstacle stroke value while the other course may have a lower effective playing length and a higher obstacle stroke value. The courses could end up with a similar ratings but no conclusions could be drawn with regards to effective playing length or obstacle stroke value.

Let's plug in some hypothetical numbers.

Rulesnut Red Course Yardage: 6000 Course Rating:70 Slope: 130

7502 (effective playing length) / 220 + 40.9 = 75 (Scratch Yardage Rating)
Obstacle Stroke Value = -5

75 (Scratch Yardage Rating) -5 (Obstacle Stroke Value) = 70 (Course Rating)

Rulesnut Blue Course Yardage: 6000 Course Rating:70 Slope: 130

5302 (effective playing length) /220 + 40.9 = 65 (Scratch Yardage Rating)
Obstacle Stroke Value = 5

65 (Scratch Yardage Rating) + 5 (Obstacle Stroke Value) = 70 (Course Rating)

A similar proof could be done for slope rating.

What conclusions can be drawn from actual course length with respect to effective playing length and obstacle stroke value? NONE.

It is funny that you mention it. Champlain is the ONLY course that has the same rating of 68 for both the blue and white tees. For ALL other courses, the difference between tees is what can be expected based on their yardage. To me it seems Champlain blue rating should be more around 69. Play the white tees if you want to lower your handicap

Again, you seem to have no faith in the rating system. Obstacles such as doglegs, fairways bunkers, trees, etc. could come into play to a greater or lesser degree depending on the tees from which you played. This has all been factored into the rating and coincidentally the tees have identical ratings. Playing from the white tees will not lower your handicap.