Scottish Crime and Justice Survey 2019-20: FOI release

Information requested

1) The Relative Standard Errors for each datapoint provided in Table A1.2 of the Scottish Crime and Justice Survey 2019-20. Please only provide the RSEs for 2019-20 figures for the categories of all SCJS crime, property crime, violent crime and comparable crime.

2) The confidence interval that was used to judge whether a rise or fall in the statistics in Table A1.2 were statistically significant. I am asking for the confidence interval as a percentage.

3) How the upper and lower estimates for the aforementioned categories of crime (all SCJS, property, violent, comparable) were calculated. For example, were these the upper and lower bounds of the confidence interval - or are they the interquartile range of the data etc. Please provide the methodology for calculating the upper and lower estimates.

Response

1) Table A1.2 in the Scottish Crime and Justice Survey (SCJS) 2019/20: Main Findings report provides the volume estimates of the extent of crime in Scotland.

The relative standard errors for the 2019/20 figures for each crime type, including all SCJS crime, property crime, violent crime and comparable crime, can be found in Section 10.1 (Table 10.1) of the 2019/20 SCJS Technical Report.

2) The SCJS gathers information from a sample rather than from the whole population and, although the sample is designed carefully, survey results are always estimates, not precise figures.

To indicate the extent of uncertainty, the SCJS Main Findings report presents key results on the extent (and prevalence) of crime using both best estimates and lower/upper estimates. The best estimate is the mean figure drawn from the sample. The lower and upper estimates are for the 95% confidence interval.

The following table provides the requested confidence intervals as a percentage for the above crime categories. At the 95% confidence level, when assessing the results of a single survey it is assumed that there is a one-in-20 chance that the true population value will fall outside the 95% confidence interval range calculated for the survey estimate. Similarly, over many repeats of a survey under the same conditions, one would expect that the confidence interval would contain the true population value 95 times out of 100.

Confidence intervals as a percentage for all SCJS crime, property crime, violent crime and comparable crime, 2019/20.

Crime category	Confidence intervals as a percentage
All SCJS crime	563,000 +/-11%
Property crime	369,000 +/-11%
Violent crime	194,000 +/-24%
Comparable crime	379,000 +/-14%

Note: the crime volumes in this table are rounded to the nearest 1,000

3) The SCJS Main Findings report presents key results on the extent (and prevalence) of crime using both best estimates and lower/upper estimates. The best estimate is the mean figure drawn from the sample. The lower and upper estimates are for the 95% confidence interval. The published 2019/20 SCJS Technical Report provides more detailed information on the methodology used for calculating confidence intervals and statistical significance in Section 10.2.

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