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12/12/2006:// The recent out of season bathing water survey carried out by Northumbrian Water is riddled with errors and shows a very poor grasp of even the most basic mathematics, according to the campaign group Surfers Against Sewage (SAS).
Analysis of the raw data used by Northumbrian Water reveals an unacceptably high number of errors including several instances of water users being removed from data tables. Other basic maths ‘mistakes’ result in situations like that at Saltburn on the 18th of December when the survey count was almost halved from 21 to 12.
While one or two mistakes are understandable, SAS highlight that the number of errors revealed is very high and every single one leads to a reduction in the estimation of water use. SAS are also concerned that many more errors may go undetected. On top of these errors, the survey methodology unjustifiably ignores any users getting in or out of the water, or using water outside of the official designated areas.
As well as Northumbrian Water showing that they lack attention to detail, the conclusions drawn from the survey also suggests they lack basic numeracy skills.
Their conclusion that none of the Bathing Waters have use exceeding an average of 10 users per week is actually based on the average number of water users they recorded in the water at any one time.
For instance, according to the data collected by Northumbrian Water, Tynemouth has an average of 4.8 surfers in the water at any one time during the survey period. According to their report, Northumbrian Water have incorrectly concluded that this means Tynemouth is used by less than 10 surfers per week.
If you assume each surfer stays in for 1 hour and that 8 hours a day are available for surfing, calculations suggests that an average of around 38 surfers at Tynemouth each day. These calculations, while no more than rough estimates made with poor data, highlight the huge errors Northumbrian Water have made in their conclusions.
According to SAS Campaigns Director Richard Hardy, “It’s a bit like quickly looking out your window, seeing three cars pass, ignoring one, miss-counting another and then concluding that the road has an average of one car using it per week. Northumbrian Water’s conclusion that their survey shows that no water has an average use exceeding 10 per week is absolutely ridiculous and is based on poor understanding of what the data they have collected actually represents. This is even before you consider the inaccuracies brought about by all the errors Northumbrian Water have made”.
The fact remains that the waters in question are very popular with recreational users outside of the bathing season, often with over 50 surfers in the water at any one time when conditions are right. Its high time Northumbrian Water acknowledged this fact and stopped wasting everyone’s time with poorly constructed arguments backed up with inaccurate and error-ridden reports.
To help put them straight SAS have reserved a place for the Managing Director at Northumbrian Water on a part-time Maths Workshop Numberskills Certificate course at Hartlepool College of Further Education starting tonight at 6pm. We hope he’ll be able to get along!
Notes:
Below is an exert from SAS’ critical assessment on Northumbrian Water’s survey, submitted to the Environment Agency as part of the consent application process
1. Northumbrian Water’s Out-of-Season Water Users Survey
1.1. Northumbrian Water carried out a survey of bathing water use outside of the bathing season, between October 2005 and April 2006. They concluded that there was little use of the bathing water during the period of the survey, and that none of the Bathing Waters have use exceeding the 10 users per week on average and thus fall into the “Little or No Use” category. These conclusions are highly flawed as will be shown below.
1.2. Incorrect Conclusions
1.2.1. According to the methodology used by Northumbrian Water, it seems that they have estimated the average number of surfers (i.e. users) per week by recording number of surfers in the water during the short site visits (which were often less than 3 minutes) and then calculating the average.
1.2.2. The figure they calculate is not in fact the average number of surfers per week but the average number of surfers in the water at any given moment.
1.2.3. It should be remembered that all users will not be in the water at the same time. There is likely to be a significant turnover of individuals so that the actual number of users per day or week is likely to be substantially larger than Northumbrian Water’s conclusions suggest.
1.2.4. To convert Northumbrian Water’s figure (average number of surfers in the water at any given moment) into the number of surfers for a given time period, an approximation similar to the following should be made:
Number of users = a x (t/l)
Where a = the number of surfers in the water at any given moment, t = the time period in hours and l = the length of time in hours an individual surfers spends in the water (note t > l).
1.2.5. Using this method, it can be seen that if the average number of surfers in the water at any given moment is 5 and the average length of time spent in the water is 1 hour, over a 2 hour period, you could expect 10 surfers to have used the water. Over a day (assuming only 8 hours is available for surfing) you could expect 40 surfers to have used the water.
1.2.6. By using these assumptions, and the average user figures derived from Northumbrian Water survey, the following table shows how they convert into more useful information.
Beach
Average number of surfers in the water (according to Northumbrian Water)
Calculated average number of surfers using the water in one day (8 hours)
Tynemouth (Longsands South)
4.8333
38.64
Saltburn
2.5625
20.5
1.2.7. It can be seen that this increases the estimate by approximately one order of magnitude. These calculations suggest that the average number of surfers in one day comes can come close to 40, which contradicts Northumbrian Water’s assumption that none of the bathing waters surveyed have use exceeding 10 users per week.
1.2.8. Contrary to Northumbrian Water’s flawed assumptions, more robust estimations suggest that this data shows that these beaches have a high usage outside of the bathing season.
1.3. The Survey Ignores Some Water Users
1.3.1. By reading the comments section of Appendix C of the survey, it is often the case that user numbers are underestimated as those getting ready to enter the water or just leaving it are not recorded.
1.3.2. For instance, at Saltburn on 01/04/06, it is noted that 3 surfers were changing in the car park but they were not considered to be ‘users’ as they were not in the water.
1.3.3. On another occasion on 13/10/05 at Tynemouth (Longsands South), it is noted that 8 surfers were in the sea 15 minutes after the ‘inspection’. Considering that the time spent for each inspection over the survey period varies considerably and the comments clearly indicate that the observers were still at the site, this omission suggests a bias in the data recorded.
1.3.4. While this inflexibility might be an accurate way of assessing the average number of surfers in the water at any given moment, it is not good way of gaining an accurate view of the number of out-of-season beach users.
1.3.5. Similarly, on 05/04/06 at Seaton Carew North, 7 surfers are seen in the water but as they are not considered to be within the ‘bathing water’, their presence is not recorded.
1.3.6. The survey methodologies inability to appreciate the real situation is not just directed toward surfers. On 01/11/05 at South Shields, one ‘divers overboat’ is noted. No divers are recorded in the water on this occasion. This is presumably because diving is carried out underwater and therefore not visible. As divers could only be seen while about to enter or having just left the water (during which time they would presumably not count as ‘users’ if the same methodology is followed as with surfers), it is unsurprising that no divers were recorded during the whole survey.
1.4. Errors in the Data Recorded
1.4.1. Analysis of the raw data gained from the surveys highlights many errors. For instance, on the 20/04/06 at King Edwards Bay, it is noted in the comments section that there was one bather in the water. Despite this, the number of bathers in the water is recorded in the table as zero.
1.4.2. On the 05/11/05 at Seaham Hall, the comments section notes 2 paddlers throwing stones. Again, the number of paddlers in the table is recorded as zero.
1.4.3. On the 29/04/06 at Redcar Coatham, the comments section reads 1 surfer, 2 just about to go in. Yet again, there are no surfers recorded in table.
1.4.4. On 18/12/05 at Saltburn, according to the comments, 7 surfers are on the south side of the pier and 14 on the north side. Instead of 21 being recorded as the number of surfers in the water, the number entered is 12.
1.4.5. While a few mistakes can be expected, the frequency of errors in this survey is unacceptably high. It should be noted that all of the errors highlighted result in a reduction of the number of water users recorded by Northumbrian Water.
1.4.6. The only reason these errors are noticeable is because of additional comments made on some occasions. Considering the lack of attention to detail given to the survey, there is every chance that other important data has been left out (and presumably defaulted to zero water users) but no additional comments are available to highlight the mistakes made. Consequently, confidence in the results should not be considered high.
1.5. Other Comments on the Survey
1.5.1. The vast majority of the site visits occurred between late morning and early afternoon. While this may be acceptable on the weekend, it should be remembered that many surfers would be restricted in the week by work hours and consequently go surfing before (i.e. early morning) or after (late afternoon to early evening). This has not been considered in the survey methodology. It could therefore be expected that mid week estimations of surfer numbers (and therefore any averages derived from them) is lower than it should be.
1.5.2. Other than occasional sporadic comment, the survey makes no attempt to record the surf conditions. It is imperative that any survey on surfer participation takes into account if the conditions are conducive to surfing as this may explain low usage on some occasions. Low participation under poor surf conditions should not be used to imply that overall usage is sporadic or low.
1.6. In conclusion, Northumbrian Water’s survey does not prove that there is little use of the water outside of the bathing season. The assumptions Northumbrian Water have drawn from their survey (which itself is riddled with errors) does not show any appreciation for what the data they collected actually represents. The lack of validity of the survey suggests it is unsuitable for use as a robust tool for estimating out-of-season water use.
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