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‘High’ Achievers?Cannabis Access and Academic Performance
Olivier Marie Ulf Zölitz Maastricht University IZA and Maastricht University
RAND
Cannabis Access and Academic Performance 2
Motivation – Wind of Change in Drug Policies
Public opinion has reached a tipping point
Cannabis Access and Academic Performance
Cannabis Access and Academic Performance 4
Motivation – Wind of Change in Drug Policies
Public policies regarding marijuana/cannabis are changing now
US: radical recent change in public opinion and policy:
Colorado & Washington have legalized in 2014
Alaska, Oregon and Washington, D.C voted in favour of legalization
California might legalize in 2016
Uruguay is the first country that fully legalizes marijuana in 2014
Europe: decriminalisation in Czech Republic, Portugal, Norway…
Cannabis Access and Academic Performance 5
Motivation – Wind of Change in Drug Policies
Cannabis Access and Academic Performance 6
Research Question
Does drug policy affect student achievement via a change in consumption behavior?
Cannabis Access and Academic Performance 7
Motivation – The Arguments
Pros: + Legalization cuts the link to illegal markets + The war on drugs is a loosing battle:
Legalization will reduce crime & cut costs of the legal system
Cons: − Easy availability will increase demand− Marijuana is a gateway drug− Negative externalities for society
Does legal access affect consumption? What are the (unintended) consequences of legalization?
Cannabis Access and Academic Performance 8
Medical Evidence: Cannabis Use and Cognitive Functioning
Bossong et al. (2013) experiment with THC admission in fMRIs:
Subjects had to recall whether they had seen information before
Conclusion: “THC impairs performance on high-level cognitive functions essential for goal-directed behavior”
Cannabis Access and Academic Performance 9
Medical Evidence: Cannabis Use and Cognitive Functioning
Gilman et al. (2014) look at young, non-dependent marijuana users and find that recreational use is associated with brain abnormalities: abnormalities in gray matter density and volume abnormalities in the shape of the nucleus accumbens and amygdala
Ranganathan & da Souza (2006) Review of medical evidence on the effects of THC:
“THC…impairs immediate and delayed free recall of information presented after, but not before, drug administration”
Cannabis Access and Academic Performance 10
Medical Evidence: Cannabis Use and Cognitive Functioning
Crean et al. (2011)
Cannabis Access and Academic Performance 11
Related Economics Literature
Pacula et al. (2003) 10th grade marijuana use is associated with a 15% reduction in std. math test
performance in 12th grade
Chatterji (2006) Adolescent marijuana consumption is related to 0.2 years less schooling
Cobb-Clark et al. (2013) Early marijuana use (age 14) predicts 8% lower high school completion rates
and lower university entrance scores
Van Ours (2011 & 2014) Individuals who grow up closer to cannabis-shops start smoking earlier Using cannabis increases the likelihood of mental health problems (onset
ages)
Cannabis Access and Academic Performance 12
The Causality Problem
The main problem is to identify the causal direction in the relationship between drug use and outcomes:
Individual consumption decision driven by unobserved factors that also affect outcomes
Policy changes are a result of general societal change (Pacula & Sevigny; 2014)
Truthful reporting of consumption is also affected by legal status and changes
Cannabis Access and Academic Performance 13
Contribution
We study a unique policy experiment that suddenly restricted legal cannabis access based on nationality
We and observe student performance before and after
We have clean identification using a difference in differences approach
We estimate the causal impact of a change in soft drug access on an educational outcome
We can provide some additional evidence on the underlying mechanisms and how soft drug use affects performance
Cannabis Access and Academic Performance 14
A Reduced Form Approach
We have a reduced form approach as we do not directly observe smoking behavior of students but only their test scores
Reduced form is informative since policy changes also affect the probability to admit consumption in questionnaire studies
Cannabis Access and Academic Performance 15
Drug Policy in the Netherlands
Basis of Dutch ‘tolerance’ policy is the Opium Law (1976) introduced to “minimize harm done to users and their environment”
Possession and retail of small quantities (< 5g) of cannabis are legal but large scale cultivation or wholesale remains illegal
Legal access exclusively via licensed ‘coffie-shops’ which must follow number of strict rules: no sales to ages <18; no advertising; etc.
25% of the Dutch municipalities have decided to allow licensed cannabis-shops
Cannabis Access and Academic Performance
Belgium
Germany
Coffee-shop density
Cannabis Access and Academic Performance 17
The Maastricht Policy Change
Proximity to borders attracted a lot of ‘drug tourists’
The City was very concerned about the drug tourism, street dealing and negative externalities for the city residents
To respond to city concerns, the coffie-shop union (VOCM) proposed to only allow Dutch, German, and Belgian (DGB) passport holders
As of October 1st, 2011 the ‘neighborhood country criterion’ was introduced in all establishments selling cannabis in Maastricht
Volume of sales before: € 100 million per year (with 40% city taxes)
Cannabis Access and Academic Performance
Cannabis Access and Academic Performance 19
Potential Effects of the Policy?
Intended effect: stop drug tourism and reduce street dealing
Indirect effect: increase in access costs for non-DGB residents and reduces consumption of marginal consumer
Although not targeted by the policy many of the 16,000 Maastricht University students were affected.
We do not directly observe smoking behavior of students but we have very good panel data on potentially affected educational outcomes:
grades, course passing, course dropout
Cannabis Access and Academic Performance 20
Data: Course Grades and Student Course Evaluations
All students taking Bachelor courses in the School of Business and Economics over 3 academic years: 2009/10 to 2011/12
Observe over 58,000 course grades for 4,800 students with 53% German, 33% Dutch, 4% Belgian and 10% Non-DGB
Teaching structure in all years is composed of 6 blocks:
4 regular blocks (2 months) + 2 skills blocks (2 weeks)
Additionally we make use of student course evaluation surveys to look at the underlying mechanisms
Cannabis Access and Academic Performance
Month - YearCannabis
AccessAcademic
YearAcademic
Period Total t
September-2009
All Access
2009/2010
1 1October-09November-09
2 2December-09January-10
3 3February-10March-10
4 4April-10May-10
5 5June-10July-10
6 6August-10September-10
2010/2011
1 7October-10November-10
2 8December-10January-11
3 9February-11March-11
4 10April-11May-11
5 11June-11July-11
6 12August-11September-11
2011/2012
1 13October-11
DGBOnly
November-112 14
December-11January-12
3 15February-12March-12
4 16April-12May-12
AllRestricted
5 17June-12July-12
6 18August-12
Cannabis Access and Academic Performance 22
Grade Distribution before and after the Policy0
.1.2
.30
.1.2
.3
0 1 2 3 4 5 6 7 8 9 10
Grade Distribution Before Access Restriction
Grade Distribution After Access Restriction
Dens
ity
Course Grades
0.1
.2.3
0.1
.2.3
0 1 2 3 4 5 6 7 8 9 10
DGB Grade Distribution
Non-DGB Grade Distribution
Dens
ity
Course Grade
Cannabis Access and Academic Performance 23
Empirical Strategy: Basic Diff-in-Diff
Adopt simple difference in differences approach to identify the causal effect of restricting cannabis access on performance
𝐶𝑜𝑛𝑡𝑟𝑜𝑙
𝑇𝑟𝑒𝑎𝑡
all access time
Let’s start by looking at this graphically. Common trends?
Other Nationalities: Non-DGB
No access
Have accessHave access
Have access
Cannabis Access and Academic Performance 24
5.4
5.6
5.8
6
6.1
6.2
6.3
6.4
6.5
6.6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Academic Period
DGB (Left Axis) All Other (Right Axis)
Graphical Analysis
No access
Have access
Cannabis Access and Academic Performance 25
Empirical Strategy: Enhanced Diff-in-Diff
Econometrically, the basic diff-in-diff coefficient is β:
Add observable individual characteristics: age, gender
For heterogeneity in course choice: # courses and course FE
Major problem of individual heterogeneity: individual FE (!)
Finally control for temporal cyclicality: period FE & time trends
Cannabis Access and Academic Performance 26
Impact of Restricted Cannabis Access on Student Grades
(1) (2) (3) (4) (5)
Std. Grade Std. Grade Std. Grade Std. Grade Std. Grade
No-access nationality * Restriction time periods 0.0595* 0.0580* 0.0709* 0.1044** 0.0926**
(0.025) (0.024) (0.029) (0.018) (0.016)
No-access nationality -0.2666* -0.2713** -0.2597*
(0.090) (0.088) (0.100)
Restriction time periods 0.0260 0.0270* 0.0423** -0.0108 0.0161
(0.013) (0.013) (0.014) (0.007) (0.019)
Observations 52,424 52,424 52,424 52,424 52,424 Number of students 4,314 4,314 4,314 4,314 4,314
R-squared 0.004 0.008 0.157 0.545 0.546 Individual Controls No Yes Yes Yes Yes Course Number & Course FE No No Yes Yes Yes Student FE No No No Yes Yes Period Dummies and Time Trend No No No No Yes
Note: Robust standard errors clustered at the nationality level reported in parenthesis.
*, and ** indicate significance at the 5 and 1 percent level respectively.
Cannabis Access and Academic Performance 27
Restricted Cannabis Access: Other outcomes
(1) (2) (3) (4)
Std. grade Passed Dropout # Courses
No-access nationality * Restriction time periods 0.0926** 0.0400** -0.0109 0.0463*
(0.016) (0.008) (0.010) (0.020)
Restriction time periods 0.0161 0.0131** -0.0123** -0.0129
(0.019) (0.003) (0.004) (0.008)
Mean of Outcome NA 0,746 0,142 2,033 Effect size NA 0,054 -0,077 0,023 Observations 52,424 52,424 57,816 57,816 R-squared 0.546 0.373 0.366 0.616
Note: Additional controls are age gender, number of courses enrolled in, Course FE, Student FE, Teaching period dummies
and time trends. Robust standard errors clustered at the nationality level reported in parenthesis. * and ** indicate significance at the 5 and 1 percent level respectively.
Cannabis Access and Academic Performance 28
Main Results - Interpretation
The cannabis prohibition raised grades by 0.09 std. deviations The treatment effect on the treated depends on the fraction of
treated consumers in the underlying population
To get some idea on baseline consumption rates we ran a survey‒ Non-DGBs who smoked marijuana in past 7 or 30 days: 26 %‒ Treatment effect on smokers: 0.09 / 0.26 = .35 SD in grades
These are large effects! Teachers 0.13-0.19 | Peers 0.01-0.19 Other reduced form: Alcohol: 0.03-0.13 | Marijuana: 0.09 Do students comply with the law / report honestly?
Cannabis Access and Academic Performance 29
Further Results
Are effects heterogeneous across subgroups?
Differences in consumption propensity and policy compliance?
What are the mechanisms?
How exactly does consumption affect university performance?
Cannabis Access and Academic Performance 30
Results by Sub-Groups
Subgroup: Coefficient on Grade Coefficient on Passing
Average passing rate
Number of observations
Female 0.1257** 0.0457** 81.69 20,380
(0.031) (0.012)
Male 0.0692** 0.0356** 77.35 37,436
(0.014) (0.009)
Younger students 0.1160** 0.0571** 77.93 28,941
(0.028) (0.014)
Older students 0.0240 0.0050 79.92 28,875
(0.031) (0.015)
Lower Performers 0.0890** 0.0472* 62.20 27,001
(0.032) (0.017)
Higher Performers 0.0555** -0.0096 94.53 26,985 (0.017) (0.009)
Note: Robust standard errors clustered at the nationality level reported in parenthesis.
*, and ** indicate significance at the 5 and 1 percent level respectively.
Cannabis Access and Academic Performance 31
Robustness Analysis: Placebo Treatments
1) Placebo in time: Is there a similar effect one year before the actual policy?
2) Placebo in nationality: Effects if we pretend Belgians instead of Non-DGB treated?
(1) (2) (3) (4)
Placebo policy - 1 year earlier
Placebo nationality - Belgians are treated
Std. Grade Passed course Std. Grade Passed course
Placebo Policy Effect -0.0129 -0.0004
0.0103 0.0284
(0.030) (0.013)
(0.048) (0.022)
Observations 34,325 34,325
48,762 48,762 R-squared 0.567 0.393
0.542 0.366
Same Controls and FE Yes Yes Yes Yes
Note: Robust standard errors clustered at the nationality level reported in parenthesis. *, and ** indicate significance at the 5 and 1 percent level respectively.
Cannabis Access and Academic Performance 32
Evidence on the Underlying Channels
The evidence from the medical literature suggests that in particular numerical problem solving skills are affected.
Can we confirm that?
What are the effects stronger for more mathematical / theoretical courses?
Cannabis Access and Academic Performance 33
Channels – Numerical vs. Non-numerical Skills
Medical literature shows that marijuana consumption harms numerical skills Are our results consistent with these findings?
(1) (2) (3) (4) Grades -
Non-Numerical
Pass - Non-
Numerical Grades -
Numerical Pass -
Numerical
No-access nationality * Restriction time periods 0.0426** 0.0231** 0.2284** 0.0733**
(0.016) (0.007) (0.028) (0.010)
Restriction time periods 0.0329 0.0024 -0.1828** -0.0554**
(0.022) (0.006) (0.029) (0.020)
Mean of Outcome NA 0.794 NA 0.663 Effect size NA 0.029 NA 0.110 All Controls and FE Yes Yes Yes Yes Observations 34,347 34,347 18,077 18,077 R-squared 0.533 0.375 0.672 0.505
Note: Robust standard errors clustered at the nationality level reported in parenthesis.
*, and ** indicate significance at the 5 and 1 percent level respectively.
Cannabis Access and Academic Performance 34
Channels – Changes in Student Course Evaluations
Mechanism CategoryNon-DGB
*RestrictionSurvey Question(s)
in Course Evaluation
Hours Worked[N = 15,987]
-0.244(0.376)
How many hours per week on average did you spend on self-study?
FeelStimulated[N = 15,937]
0.087(0.059)
‘The learning materials stimulated me to start and keep on studying’ & ‘…stimulated discussion with my fellow students.’
FunctionsWell[N = 15,997]
0.032(0.064)
‘overall functioning of your tutor…’ &‘My tutorial group has functioned well.’
UnderstandBetter[N = 13,520]
0.122*(0.064)
‘The lectures contributed to a better understanding…’ & ‘Working in tutorial groups helped me to better understand the subject matters of this course’
QualityImproved[N = 15,897]
0.017(0.061)
‘The tutor sufficiently mastered the course content of this course’ & ‘give overall grade for the quality of this course´
Cannabis Access and Academic Performance 35
Are there spill overs in the classroom?
Given the large effect, can we identify classroom spillovers?
Does being in class with a high share of treated increase grades?
Cannabis Access and Academic Performance 36
Peer effects? – Effect of Fraction Treated in Section
(1) (2) (3)
Std. grade Pass Dropout
No-access nationality * Restriction time periods * Share no-access nationality 0.1670 0.2109* 0.0128
(0.133) (0.080) (0.084)
No-access nationality * Restriction time periods 0.0772** 0.0214* -0.0122
(0.020) (0.010) (0.009)
Restriction time periods 0.0144 0.0159** -0.0073
(0.029) (0.002) (0.006)
Restriction time periods * Share no-access nationality 0.0370 -0.0153 -0.0574
(0.125) (0.030) (0.032)
Share of no-access nationality in class -0.0017 -0.0066 0.0080
(0.068) (0.027) (0.015)
Observations 52,395 52,395 57,782
R-squared 0.546 0.373 0.366
Individual Controls Yes Yes Yes
Course Number & Course FE Yes Yes Yes
Student FE Yes Yes Yes
Period Dummies and Time Trend Yes Yes Yes
Note: Robust standard errors clustered at the nationality level reported in parenthesis. *, and ** indicate significance at the 5 and 1 percent level respectively.
Cannabis Access and Academic Performance 37
Conclusion
To our knowledge first causal evidence on how drug policy affects performance
Results are only a part of what has to be considered in societal cost-benefit analysis of drug policies
Effects are perhaps not symmetric for prohibition and legalization
We provide solid evidence that restricting legal access to cannabis increases university performance
In line with clinical evidence the channels point to improved understanding and improved numerical skills
Cannabis Access and Academic Performance 3838
.
End of slideshow, click to exit.
Cannabis Access and Academic Performance 39
Motivation – Wind of Change in Drug Policies
Cannabis Access and Academic Performance 40
5.4
5.6
5.8
6
6.1
6.2
6.3
6.4
6.5
6.6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17Academic Period
DGB (Left Axis) All Other (Right Axis)
Graphical Analysis
No access
Have access
Cannabis Access and Academic Performance 41
Differences in observables between DGB and non-DGB students
Student nationality All DGB Non-DGB Difference Min Max
Grade 6.5355 6.5688 6.0996 -.4693*** 1 10Passed course .7892 .7959 .7010 -.0949*** 0 1Course dropout .0935 .0906 .1296 .0390*** 0 1Observations 57903 53622 4281
Student nationality All DGB Non-DGB Difference Min Max
Female .3526 .3480 .4077 .0446*** 0 1
Age 20.27 20.29 20.21 .1002*** 16.24 39.73
Final GPA 6.5656 6.6142 5.9770 -.5288*** 1 9.75
Courses enrolled 1.9927 1.9876 2.0556 -.06794*** 1 5
Observations 4419 4083 336
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