5. Bringing together crime statistics
Why are there two sources of crime statistics?
This chapter compares the Scottish Crime and Justice Survey (SCJS) and police recorded crime to help assess whether and to what extent they show consistent trends. It examines the scale of the difference between the volume of crime that is recorded by the police and the level of crime that is estimated by the survey to be experienced by the adult population living in households in Scotland. This builds on an analytical paper published in 2014.
A range of information is provided based on analysis of a sub-set of comparable crimes. The two sources of crime statistics are reviewed briefly first, then the chapter looks at trends in these two sources over time, including a specific focus on three broadly comparable sub-groups: violent crime, acquisitive crime and vandalism. Finally this chapter compares police recorded crime with the proportion of SCJS crime estimated to have been reported to the police.
The SCJS and police recorded crime are essential, complementary evidence sources that, when considered together, present a fuller picture of crime in Scotland.
Police recorded crime captures a broad range of crimes that are recorded by the police. It provides a good measure of crimes that are well-recorded and reported to the police and is particularly useful for lower-volume crimes that are challenging for sample surveys of the population to capture. Police recorded crime is used to develop and evaluate measures put in place to reduce crime, and to assess the performance of policing and criminal justice organisations. However, this data is sensitive to changes in recording practices and police activity, and does not include information about crimes that are not reported, or recorded by, the police.
Crime surveys allow a wider assessment of the overall level of crime and likelihood of experiencing crime. They also provide a range of additional information, for example on the characteristics of crime, the relative likelihood of experiencing crime across the population and on repeat victimisation. However, surveys are often not as good at picking up some rarer crimes, crimes where there is no specific victim, or where the victim is not covered by the survey sample (for example, crimes against businesses and children).
As well as these differences, the SCJS and police recorded crime also cover different timescales. The 2018/19 Recorded Crime results cover crimes recorded during the 2018/19 financial year. Whereas the 2018/19 SCJS includes crimes experienced by SCJS respondents over a 25-month 'reference period'.
Overall, the two sources each feature relative strengths and limitations, making them more appropriate in different contexts and for different purposes. Taking account of these differences, comparisons between recorded crime and SCJS data can be made by examining a broadly comparable sub-set of crimes which are covered by each source. This sub-set of crimes are made up of those crimes that are coded in the survey in approximately the same way as they would be recorded by the police. Almost two-thirds (64%) of 'all SCJS crime', as measured by the 2018/19 SCJS, fall into categories that can be compared with police recorded crime.
What are the trends in comparable SCJS and police recorded crime?
There is relatively good consistency in the trends in overall comparable SCJS and police recorded crime, particularly over the longer term, with both showing large decreases.
Of the 573,000 crimes estimated by the 2018/19 SCJS, almost two-thirds (366,000) can be compared with police recorded crimes. Figure 5.1 demonstrates the scale of the difference between the two series of crime statistics. In 2018/19, the police recorded 125,953 crimes and offences in the comparable sub-set, representing approximately 34% of the number of crimes in the SCJS comparable sub-set.
Sources: SCJS, Police recorded crime.
There are a number of reasons for these differences, including that SCJS estimates tend to be higher than recorded crime figures, even in the comparable category, because the survey is able to capture crime which does not come to the attention of the police. Overall, from the answers given by respondents in the survey when asked if the police came to know about an incident, the 2018/19 SCJS estimates that 41% of all crime in the comparable sub-set came to the attention of the police.
Both the SCJS and police recorded crime provide evidence of large decreases in crime in Scotland over the last decade or so. As shown in Table 5.1, the SCJS estimates that the volume of comparable crime fell by 50% between 2008/09 and 2018/19, whilst comparable recorded crime is down by 42% over the same period.
Table 5.1: Comparable crime group estimates, 2008/09 to 2018/19
|2008/09||2017/18||2018/19||% change since 2008/09||% change since 2017/18|
|All comparable crime|
|Comparable SCJS Crime||731,000||386,000||366,000||-50%||No change|
|Comparable Recorded Crime||215,901||130,418||125,953||-42%||-3%|
|SCJS Acquisitive Crime||64,000||51,000||46,000||-28%||No change|
|Recorded Acquisitive Crime||27,527||17,867||16,644||-40%||-7%|
|SCJS Violent Crime||317,000||172,000||165,000||-48%||No change|
|Recorded Violent Crime||82,855||63,835||63,771||-23%||-0.1%|
|SCJS Vandalism||350,000||163,000||155,000||-56%||No change|
Sources: SCJS; Police recorded crime; SCJS Base: 2008/09 (16,000); 2016/17 (5,570); 2017/18 (5,480); 2018/19 (5,540).
Note: changes in SCJS results specified where statistically significant.
Since 2017/18, the SCJS found no change in the level of comparable crime, whilst comparable recorded crime fell by 3%.
In 2016, Her Majesty's Inspectorate of Constabulary in Scotland (HMICS) published an audit of incidents and crimes recorded by Police Scotland. This audit found no systematic data quality issues around the recording of crimes and offences, with the resulting report stating that 'the quality of most incident and crime recording decisions by Police Scotland is good'.
The following section looks at comparable acquisitive crime, violent crime and vandalism in more detail.
The acquisitive comparable crime group includes bicycle theft, housebreaking and theft of a motor vehicle. In 2018/19 the SCJS estimated that there were 46,000 acquisitive crimes (+/- 11,000, meaning that the true number of acquisitive crimes experienced by the population is estimated to be between 35,000 and 57,000). The police recorded 16,644 acquisitive crimes in 2018/19.
Both SCJS estimates and recorded acquisitive crime figures decreased between 2008/09 and 2018/19 (by 28% and 40% respectively). Since 2017/18 police recorded acquisitive crime has decreased by 7%, while the SCJS found no change in acquisitive crime. This is likely to be due in part to the smaller sample sizes involved, which means it can be more challenging to identify significant changes between adjacent survey years.
Violent comparable crime includes serious assault, minor assault and robbery. In 2018/19 the SCJS estimated that there were 165,000 violent crimes (+/- 44,000, meaning that the true number of violent crimes experienced by the population is estimated to be between 121,000 and 209,000), while the police recorded 63,771 violent crimes.
Table 5.1 shows that the two sources of comparable violent crime data both show large decreases over the longer term, but broadly stable figures since 2017/18. Between 2008/09 and 2018/19, both SCJS estimates and police recorded violent crime figures have shown a decrease (by 48% and 23% respectively). Since 2017/18, comparable police recorded violent crime has shown a small decrease of 64 incidents, while the SCJS has found no change in violent crime.
The vandalism comparable crime group includes motor vehicle vandalism and property vandalism. In 2018/19 the SCJS estimated that there were 155,000 instances of vandalism (+/- 24,000, meaning that the true number of vandalism crimes experienced by the population is estimated to be between 130,000 and 179,000). The police recorded 45,538 vandalism crimes in 2018/19.
The trends in comparable crimes of vandalism across both the SCJS and police recorded crime between 2008/09 and 2018/19 are very similar – with the SCJS showing a decrease of 56% and police recorded crime showing a decrease of 57%. Since 2017/18 there has been no change in the SCJS estimate of vandalism, while crimes of vandalism recorded by the police have fallen by 7%.
An alternative approach to investigating the relationship between the two sources is to examine the amount of police recorded crime against the volume of SCJS crime estimated to have been reported to the police.
SCJS respondents are asked whether the police 'came to know about' the crime, either from them or somebody else. This allows comparisons to be made between comparable crime estimated to have been reported to the police in the SCJS (i.e. a sub-set of comparable crime), and police recorded crime figures.
The previously cited analytical paper, published in 2014, outlined two methods for calculating this: the first, comparing the (at that time) biennial SCJS to annual recorded crime figures and the second comparing the (at that time) biennial SCJS against two reporting years of averaged police recorded crime data. This section updates the information using the first method, to compare now annual SCJS estimates to annual recorded crime figures. Although it is not possible to determine on an individual basis whether a crime that the police 'came to know about' was captured in police recorded crime data, this type of analysis can give an indication of the level of crime that goes unreported, and the broad relationship between police recorded crime figures and SCJS estimates.
Figures from the 2018/19 SCJS indicate that of the 366,000 crimes in the overall comparable sub-set, around 149,000 incidents (41%) were estimated to have been reported to police. Figure 5.2 displays the difference by volume between SCJS comparable crimes estimated to be reported to the police (as a sub-set of all SCJS crime) and police recorded crime for all years since 2008/09.
Sources: SCJS; Police recorded crime.
In 2018/19, the police recorded 125,953 crimes in the comparable category. It is therefore estimated that around 85% of comparable crime estimated to be reported to the police was recorded by the police in 2018/19. Figure 5.3 shows how this figure has varied over time.
Sources: SCJS; Police recorded crime.
This type of analysis can be extended across the comparable crime sub-groups, where similar results are found. For example, around 67,000 violent crimes are estimated to have been reported to the police in 2018/19 (or 39% of the number of violent crimes estimated by the SCJS), while the police recorded 63,771 violent crimes. It is therefore estimated that almost all (95%) of comparable violent crime estimated to be reported to the police was recorded by the police in 2018/19.