diff --git a/DESCRIPTION b/DESCRIPTION
index d652038a..e6df7330 100755
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -7,19 +7,40 @@ Authors@R: c(
         given = c("Matthijs", "S."),
         family = "Berends",
         email = "m.s.berends@umcg.nl",
-        role = c("aut", "cre"),
+        role = c("aut", "dis", "cre"),
         comment = c(ORCID = "0000-0001-7620-1800")),
     person(
         given = c("Christian", "F."),
         family = "Luz",
         email = "c.f.luz@umcg.nl",
-        role = c("aut", "ctb"),
+        role = c("aut", "dis"),
         comment = c(ORCID = "0000-0001-5809-5995")),
     person(
         given = c("Erwin", "E.A."),
         family = "Hassing",
         email = "e.hassing@certe.nl",
-        role = "ctb"))
+        role = "ctb"),
+    person(
+        given = "Corinna",
+        family = "Glasner",
+        email = "c.glasner@umcg.nl",
+        role = "ths",
+        comment = c(ORCID = "0000-0003-1241-1328")),
+    person(
+        given = c("Alex", "W."),
+        family = "Friedrich",
+        email = "alex.friedrich@umcg.nl",
+        role = c("ths", "ldr"),
+        comment = c(ORCID = "0000-0003-4881-038X")),
+    person(
+        given = "Bhanu",
+        family = "Sinha",
+        email = "b.sinha@umcg.nl",
+        role = "ths",
+        comment = c(ORCID = "0000-0003-1634-0010")),
+    person(
+        family = "University of Groningen",
+        role = "uvp"))
 Description: Functions to simplify the analysis of Antimicrobial Resistance (AMR)
     of microbial isolates, by using new S3 classes and applying EUCAST expert rules
     on antibiograms according to Leclercq (2013)
diff --git a/NEWS.md b/NEWS.md
index 80c5afdb..52828cad 100755
--- a/NEWS.md
+++ b/NEWS.md
@@ -58,6 +58,7 @@
 
 #### Other
 * Unit testing for all Linux and macOS releases of R 3.1 and higher: https://travis-ci.org/msberends/AMR
+* Added thesis advisors to DESCRIPTION file
 
 # 0.2.0 (latest stable version)
 **Published on CRAN: 2018-05-03**
diff --git a/R/freq.R b/R/freq.R
index ad832703..9346a233 100755
--- a/R/freq.R
+++ b/R/freq.R
@@ -326,7 +326,7 @@ frequency_tbl <- function(x,
       header <- header %>% paste0(' (unique: ', boxplot.stats(x)$out %>% n_distinct(), ')')
     }
   }
-  if (any(class(x) == "rsi")) {
+  if (NROW(x) > 0 & any(class(x) == "rsi")) {
     header <- header %>% paste0('\n')
     cnt_S <- sum(x == "S")
     cnt_I <- sum(x == "I")
diff --git a/README.md b/README.md
index b68843fc..6fbee0e2 100755
--- a/README.md
+++ b/README.md
@@ -6,14 +6,17 @@ This R package was created for academic research by PhD students of the Faculty
 :arrow_forward: Download it with `install.packages("AMR")` or see below for other possibilities.
 
 ## Authors
-
-  - [Berends MS](https://github.com/msberends)<sup>1,2</sup>, PhD Student
-  - [Luz CF](https://github.com/ceefluz)<sup>1</sup>, PhD Student
-  - [Hassing EEA](https://github.com/erwinhassing)<sup>2</sup>, Data Analyst (contributor)
+<a href="https://orcid.org/0000-0001-7620-1800"><img src="https://cran.r-project.org/web/orcid.svg" height="16px"></a> Matthijs S. Berends<sup>1,2,a</sup>,
+<a href="https://orcid.org/0000-0001-5809-5995"><img src="https://cran.r-project.org/web/orcid.svg" height="16px"></a> Christian F. Luz<sup>1,a</sup>,
+Erwin E.A. Hassing<sup>2</sup>,
+<a href="https://orcid.org/0000-0003-1241-1328"><img src="https://cran.r-project.org/web/orcid.svg" height="16px"></a> Corinna Glasner<sup>1,b</sup>,
+<a href="https://orcid.org/0000-0003-4881-038X"><img src="https://cran.r-project.org/web/orcid.svg" height="16px"></a> Alex W. Friedrich<sup>1,b</sup>,
+<a href="https://orcid.org/0000-0003-1634-0010"><img src="https://cran.r-project.org/web/orcid.svg" height="16px"></a> Bhanu Sinha<sup>1,b</sup>
   
-<sup>1</sup> Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands
-
-<sup>2</sup> Certe Medical Diagnostics & Advice, Groningen, the Netherlands
+<sup>1</sup> Department of Medical Microbiology, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands<br>
+<sup>2</sup> Certe Medical Diagnostics & Advice, Groningen, the Netherlands<br>
+<sup>a</sup> R package author and dissertant<br>
+<sup>b</sup> Thesis advisor
 
 <a href="https://www.rug.nl"><img src="man/figures/logo_rug.png" height="60px"></a>
 <a href="https://www.umcg.nl"><img src="man/figures/logo_umcg.png" height="60px"></a>