confidence interval, and 3) Determine whether the
percentage of the primary data in the census tracts falls
into the confidence interval, obtain the value of the
local S-index, and calculate the global S-index.
There are two critical values. One of them is the
global S-index. Another is the local index, which is
applied to identify statistically significant changes on
the micro-scale (local changes). The local S-index has
three values (−1, 0, 1), which means the base dataset
is lower than, similar, or higher than the test dataset
in a spatial unit, respectively. The global S-index
value is the count of the local S-index, which equals
zero, and then divides the number of all spatial units.
The value of the global S-index ranges from 0 (no
similarity) to 1 (perfect similarity), and 0.80 is used
as the threshold to indicate that two spatial point
patterns are similar. Furthermore, we used Moran’s I
to explore the spatial autocorrelation of local changes
to observe the epidemical impact on local areas.
3.2.3 Crime Trend Discovery
As the continuing pandemic of the COVID-19, many
of us face a long-term impact on our lives. Since the
COVID-19 pandemic and the resulting economic
recession have negatively affected many people’s
financial situation and mental health, people’s lives
and relations have dramatically changed over the past
years. Our research expects to discover the local
crime trends in Montgomery during the COVID-19.
As a branch of artificial intelligence, machine
learning is used in many areas that enable a computer
to learn without being explicitly programmed.
Machine learning has already been applied to
COVID-19 related research in these years; however,
few research studies are focused on criminal justice.
Thaipisutikul, et al., in 2021 proposed a framework
to classify the illegal and violent activities from
online Thai news during the COVID-19 pandemic. In
our research, the hidden correlations between crime
trends and the effect of the pandemic are challenging
to disclose; therefore, we apply machine learning to
reveal the relationships between the number of
reporting crimes and the number of COVID-19 cases
in Montgomery from March 13, 2020 to March 13,
2021. We rely on two types of COVID-19 cases in
Montgomery; one is the number of confirmed cases,
and the other is the number of deaths caused by
COVID-19.
Our research adopts one of the most widely used
machine learning methods, supervised learning.
Under supervised learning, the data set is well
labeled; every data instance is tagged with a pre-
defined category. Therefore, each data example is a
pair that consists of an input (X) and corresponding
output (Y). During the training phase, labeled data
has been fed into a machine learning algorithm, which
produces a mapping function to map the input data
with the output value. The generated mapping
function can map the unseen examples to a label in
the test step. Some widely used metrics can be applied
to evaluate the performance of the inferred function
used in the test data. In a word, supervised learning
aims to learn a mapping function from the labeled
data and discover the relationship between the input
and data output. Supervised learning can further be
categorized into classification and regression.
Because our data output is continuous, we will apply
the regression to our research.
To investigate the relationship between the crime
trends and the COVID-19 pandemic, we examine
how the confirmed cases or/and deaths affect the
number of total crimes and the number of individual
crime types in Montgomery. In our research study,
the number of crimes in Montgomery is used as the
output (Y); the number of confirmed cases or/and
deaths is used as input of data (X). We use two state-
of-art machine learning algorithms to fulfill our tasks,
the Support Vector Regression (SVR) and the Linear
Regression. SVR uses the same strategy as Support
Vector Machine (SVM) but is used for regression
tasks. Linear regression models a linear relationship
between input variables and the single output.
Additionally, we use the Root Mean Square Error
(RMSE) method to evaluate the regression
performance of machine learning models.
4 RESULTS AND DISCUSSION
There were 22,944 criminal cases in Montgomery
County from March 13, 2020 to March 13, 2021.
Compared to the pre-pandemic year of 2019 (i.e.,
March 13, 2019 to March 12, 2020), total crime fell
by around 8.26%. For different types of crime, the
numbers of burglary, larceny, traffic violations,
vehicle theft, simple assault, and suicide decreased by
27.47%, 25.30%, 19.72%, 13.43%, 2.91%, and
1.52%, while the numbers of manslaughter,
aggravated assault, robbery, murder, domestic crime,
and rape increased by 42.24%, 38.36%, 18.86%,
14.43%, 6.02%, and 4.41% (Table 1). The number of
crimes of different crime types and the rate of crime
change one year after (March 13, 2020 to March 12,
2021) and before (March 13, 2019 to March 12, 2020)
the first COVID-19 confirmed case are illustrated in
Table 1. The symbol "+" means an increment, and
the symbol "−" refers to a decrement.