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Table 4 Multivariate negative binomial regression model on the willingness to use a CE-drug (n = 2,887)

From: Evaluating the drivers of and obstacles to the willingness to use cognitive enhancement drugs: the influence of drug characteristics, social environment, and personal characteristics

  IRR a 95% CI b
Drug characteristics   
Magnitude of enhancement effect (Ref. 5 percent):   
▪ a factor of two 1.010 [0.849,1.201]
▪ a factor of three 1.329** [1.120,1.577]
Probability of enhancement effect (Ref. 5 percent):   
▪ 50 percent 1.287** [1.081,1.533]
▪ 100 percent 1.392*** [1.177,1.646]
Severity of side effects (Ref. very light depression):   
▪ moderate depression 0.924 [0.781,1.093]
▪ very strong depression 0.881 [0.746,1.041]
Probability of side effects (Ref. one of 1,000,000 users):   
▪ one of 1,000 users 0.955 [0.815,1.119]
▪ every user 0.634*** [0.533,0.754]
Drug price (Ref. free):   
▪ 20 Euros 1.118 [0.955,1.310]
▪ 100 Euros 0.683*** [0.572,0.815]
Social environment   
Peer prevalence (Ref. none):   
▪ every second 1.287*** [1.089,1.522]
▪ every one 1.321** [1.113,1.568]
Social suggestions (Ref. never):   
▪ sometimes 0.887 [0.749,1.051]
▪ very often 1.071 [0.907,1.265]
Social disapproval (Ref. no criticism):   
▪ moderate criticism 0.926 [0.788,1.090]
▪ very strong criticism 0.713*** [0.600,0.846]
Personal characteristics   
Risk attitudes 1.012 [0.980,1.045]
Academic procrastination 1.112** [1.034,1.196]
Study motivation 0.897** [0.839,0.960]
Cognitive test anxiety (CTA) 1.383*** [1.245,1.535]
Competencies 1.048 [0.915,1.199]
Internalized social norms 0.673*** [0.644,0.702]
Prior CE-drug use 2.409*** [1.873,3.097]
Demographic variables   
Male (Ref. female) 0.949 [0.812,1.110]
Agec 0.969 [0.928,1.012]
Field of study (Ref. sports):   
▪ Linguistics & cultural studies 1.260 [0.792,2.004]
▪ Legal, economic, & social sciences 1.237 [0.763,2.006]
▪ Mathematics & natural sciences 1.261 [0.797,1.995]
▪ Human medicine & health 1.272 [0.710,2.279]
▪ Agriculture, forestry, & nutritional sciences 1.285 [0.716,2.307]
▪ Engineering 1.845* [1.089,3.126]
▪ Arts & science of art 1.669 [0.981,2.839]
Log-pseudolikelihood (full model) -3566.2
Log-pseudolikelihood (base model) -3848.1
  1. *p < 0.05, **p < .01, ***p < .001 (Wald tests, robust standard errors).
  2. a Adjusted Incidence Rate Ratios (IRR).
  3. b Confidence Intervals (CI).
  4. c Age was treated as a metric variable (see Table 2 for the 14 measured categories).