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Improving victimisation estimates from the Crime Survey for England and Wales

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This slide pack describes why we’ve changed our method for calculating repeat victimisation on the Crime Survey for England and Wales. It also describes what we have done, and its effect on the estimates we produce.

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Improving victimisation estimates from the Crime Survey for England and Wales

  1. 1. 1 Improving victimisation estimates from the Crime Survey for England and Wales (CSEW) Joe Traynor 24 January 2019 CSEW survey manager Centre for Crime and Justice
  2. 2. We’ve changed how repeat victimisation is estimated • This includes a small change to the survey weights. • Repeat victimisation is defined as the same thing, done under the same circumstances, probably by the same people, against the same victim. 2
  3. 3. We’ve replaced the cap of 5 from the old methodology • This was a limit on the number of repeat incidents included in the estimates. • We’ve replaced this limit with the 98th percentile value. • We’ve adjusted the weights used on the survey to better suit the inclusion of these higher counts. 3
  4. 4. There has been no impact on the long-term picture of total crime • However, the number of incidents for total CSEW crime are slightly higher across the entire time series than previously published. • Since the year to March 2002, the average increase in total CSEW crime (excluding fraud and computer misuse) was 2.8%. 4
  5. 5. The increase is primarily seen in violent offences • Since the year to March 2002 CSEW, estimates of violence have increased between 6.4% and 31.6% than previously published. This is due to repeat incidents being more common in violent offences. • For most crime types, the estimated number of incidents is unaffected. 5
  6. 6. The number of victims of crime is almost identical • The new cap doesn’t impact the number of victims. • However, the small change to the survey weights had a marginal effect on all crime survey estimates. • For example, for the year to March 2018 CSEW, the estimated number of victims of violent crime increased by 0.4%. 6
  7. 7. Published data • Estimates using this new methodology are published for the first time in the Crime in England and Wales: year ending September 2018 release on 24 January 2019. • Users should not use releases published before January 2019 for estimates on the number of incidents from the crime survey. 7
  8. 8. 8 Why we’ve changed our method
  9. 9. We interview one adult from each household selected for the Crime Survey for England and Wales (CSEW) sample. We ask them whether they have been a victim of any crime in the last 12 months. 9
  10. 10. Measuring incidents of crime Sometimes a respondent reports being a victim of multiple crimes that are each isolated incidents differing in nature. These incidents are counted separately. 10 Fraud 1 incident + Theft 1 incident + Violence 1 incident + Violence 2 1 incident = 4 incidents
  11. 11. Series of incidents Occasionally, we find people have been victims of the same thing, done under the same circumstances, probably by the same people. We call these a series of incidents. 11 Fraud 1 incident + Theft 1 incident + Violence 1 incident + Violence 2 3 incidents = 6 incidents
  12. 12. To gain estimates of the actual amount of crime in England and Wales, we multiply respondents’ answers by around 1,300 We survey around 1 in every 1,300 people 12
  13. 13. Total incidents experienced by respondent 1 + 1 + 1 + 3 = 6 This respondent represents 1,300 people so we multiply their answers by around 1,300 Fraud: 1 incident + Theft: 1 incident + Violence A: 1 incident + Violence B: 3 incidents Total incidents counted 1,300 x 6 = 7,800 Weight Out of around 1,300 adults in the population we interviewed this adult in this household. Incident count Weight x incidents 13
  14. 14. Occasionally people report being a victim of a large number of repeat incidents. The number of such victims included in the survey, varies from year to year. This can lead to volatility in the data. Volatility in the data 14
  15. 15. Total incidents experienced by respondent 1 + 1 + 1 + 95 = 98 Weight Out of around 1,300 adults in the population we interviewed this adult in this household. This respondent represents 1,300 people so we multiply their answers by around 1,300 Violence B - 97 incidents Total incidents counted 1,300 x 98 = 127,400 Fraud: 1 incident + Theft: 1 incident + Violence A: 1 incident + Violence B: 95 incidents Incident count Weight x incidents 15
  16. 16. The number of incidents can change dramatically between years This makes it difficult to determine trends 16
  17. 17. When the survey was set up in 1981, it was decided to cap the number of incidents that can be counted within a series. This was set at a maximum of 5. Removing this volatility 17
  18. 18. Total incidents experienced by respondent 1 + 1 + 1 + 95 = 98 Weight Out of around 1,300 adults in the population we interviewed this adult in this household. This respondent represents 1,300 people so we multiply their answers by around 1,300 Violence B - 97 incidents Total incidents counted 1,300 x 98 = 127,400 Fraud: 1 incident + Theft: 1 incident + Violence A: 1 incident + Violence B: 95 incidents Incident count Weight x incidents 18
  19. 19. Total incidents experienced by respondent 1 + 1 + 1 + 5 = 8 Weight Out of around 1,300 adults in the population we interviewed this adult in this household. This respondent represents 1,300 people so we multiply their answers by around 1,300 Violence B - 97 incidents Total incidents counted 1,300 x 8 = 10,400 Fraud: 1 incident + Theft: 1 incident + Violence A: 1 incident + Violence B: 5 offences Incident count with cap Weight x incidents 19
  20. 20. Capping the number of incidents reduces volatility This makes it possible to discern trends over time 20
  21. 21. However… • We now know that the arbitrary cap of 5 disregards a lot of incidents, especially acts of violence. • Victims of violence are more likely to be repeat victims. 21
  22. 22. 22 0 20 40 60 80 100 Violence Theft Offences Criminal damage Robbery Percentageofincidents INCLUDED EXCLUDED 40% of violent incidents were excluded in this CSEW survey year compared to only 9% of theft offences. Proportion of CSEW incidents excluded by crime type, example taken from the year ending March 2017
  23. 23. 23 between handling volatility in the estimates and not disregarding a lot of incidents A balance was needed
  24. 24. To find this balance we… • commissioned an independent review • ran a public consultation • sought advice from the National Statistician’s Crime Statistics Advisory Committee • published our decisions in response to the consultation in November 2016 24
  25. 25. We decided to… • remove the arbitrary limit of 5 • move to the 98th percentile value where this value is greater than 5 • adjust the weights used on the survey to better suit the inclusion of these higher counts • publish the uncapped data with caveats to their use as they are subject to considerable volatility 25
  26. 26. Calculating the 98th percentile • Order the victims (across 3 years) by the number of repeat incidents they have experienced. • Find the victim who is at the 98th percentile, that is, below which 98% of victims are found. • Use the number of repeat incidents experienced by that victim. 26
  27. 27. 27 We now include a much higher volume of violent incidents reported by respondents What does this mean in practice?
  28. 28. 28 0 10 20 30 40 50 Jan '95 to Dec '95 Apr '07 to Mar '08 Apr '16 to Mar '17 Apr '17 to Mar '18 Percentage of incidents Proportion excluded with 98th percentile Proportion excluded with Cap of 5 Proportion of violent incidents excluded by methodology for a selection of survey years
  29. 29. The overall picture hasn’t changed, the number of incidents has increased across the whole series What’s the impact on total crime? 29
  30. 30. 30 0 5,000 10,000 15,000 20,000 Jan '81 to Dec '81 Jan '87 to Dec '87 Jan '93 to Dec '93 Jan '97 to Dec '97 Apr '01 to Mar '02 Apr '03 to Mar '04 Apr '05 to Mar '06 Apr '07 to Mar '08 Apr '09 to Mar '10 Apr '11 to Mar '12 Apr '13 to Mar '14 Apr '15 to Mar '16 Apr '17 to Mar '18 Numberofincidents(thousands) Capped at 5 98th percentile Total CSEW crime excluding fraud and computer misuse by old and new methodology, year ending December 1981 to year ending March 2018
  31. 31. The overall picture is broadly similar, the number of incidents has increased across the whole series What is the impact on violent crime? 31
  32. 32. 32 0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000 Jan '81 to Dec '81 Jan '87 to Dec '87 Jan '93 to Dec '93 Jan '97 to Dec '97 Apr '01 to Mar '02 Apr '03 to Mar '04 Apr '05 to Mar '06 Apr '07 to Mar '08 Apr '09 to Mar '10 Apr '11 to Mar '12 Apr '13 to Mar '14 Apr '15 to Mar '16 Apr '17 to Mar '18 Numberofincidents(thousands) Capped at 5 98th percentile This rise in violence that we see here is a genuine reflection of sustained higher volumes of repeat incidents Being reported by respondents around this time-period. Across financial years, new violence estimates will be between 6% to 32% higher than previously published estimates
  33. 33. What’s next • We plan to publish microdata containing: • new crime category variables based on the 98th percentile • new crime category variables with the removal of the cap altogether for specialist users to conduct their own analyses • We are also planning a new strand of research on the extent and characteristics of repeat victimisation. 33
  34. 34. In summary: how have we changed the way we treat CSEW data back to 1981? For some crimes where repeat victimisation appears more frequently in the untreated data, the cap of 5 was too stringent. We have decided to use the 98th percentile count for each of these crime types instead. No change Maximum number of incidents in a series remains at 5 where 98th percentile is below this level. Otherwise maximum number of incidents reflects the 98th percentile count of number of incidents for that crime type. • Burglary • Other Household Theft • Personal Theft Offences • Vehicle Crime • Bicycle Theft • Robbery • Fraud • Computer Misuse Violence New maximum values from 1981 to 2018 range between 8 - 20. Criminal damage For some years between 1981 and 2018 a maximum value of 9 will be applied. Weights The inclusion of more count data from violence has meant that we have had to pay more attention to the impact of extreme weights and alter they way in which we treat these cases. 34

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