de Swart et al. (2003)


Treatment Groups

Note: Scroll about 80% of the way down the page to read the summary of the intervention procedures.


 C =  Clinician

 EBP =  evidence-based practice

 LSVT = Lee Silverman Voice Treatment 

 NA = not applicable 

 P =  Patient or Participant

 PLVT = Pitch Limiting Voice Treatment

 PD =  Parkinson’s disease

 pmh =  Patricia  Hargrove, blog developer

 SLP =  speech–language pathologist

SOURCE: de Swart, B. J. M., Willemse, S. C., Massen, B. A. M., & Horstink, M. W. I. M. (2003). Improvement of voicing in patients with Parkinson’s disease by speech therapy. Neurology, 60, 498-500.


DATE: January 29, 2021

ASSIGNED GRADE FOR OVERALL QUALITY:  No grade assigned. This was not an intervention investigation, rather it could be considered ‘proof-of-concept’ research in which information from a single 30-minute procedure has application for the development of an intervention procedure.  

TAKE AWAY: This clinically related (not clinical intervention) research compares Pitch Limiting Voice Treatment (PLVT), Lee Silverman Voice Treatment (LSVT), and habitual speaking style to determine if PLVT can increase loudness like LSVT and also modulate pitch to avoid increased pitch level. This single session task served as a proof of concept for PLVT because the investigation indicated that both PLVT and LSVT resulted in increased loudness but only PLVT limited pitch increases.

1.  What type of evidence was identified? 

•  What was the type of evidence? Single Group Experimental Design with 3 tasks and 3 conditions (i.e., a repeated measure design) 

•  What was the level of support associated with the type of evidence? Level =  Not Applicable (NA); this was not an intervention investigation

2.  Group membership determination: 

•  If there was more than one group, were participants (Ps) randomly assigned to groups? Not Applicable (NA)

3.  Was administration of intervention status concealed?

  from participants? No

•  from clinicians? No

•  from analyzers? Unclear  

4.  Was the group adequately described?  Yes 

– How many  Ps were involved in the study? 

•  total # of Ps: 32

•  # of groups: 1


•  cognitive skills: Ps with dementia were excluded

•  expressive language: Ps who were diagnosed as having “severe, hardly intelligible dysarthria” (p.498) were excluded

•  diagnosis: Parkinson’s disease (PD)

•  social/emotional status: Ps with depression were excluded

•  neurological status: Ps with other comorbid neurological conditions were excluded 

•  hearing status: Ps with hearing loss were excluded

•  previous speech therapy: Ps with a history of speech therapy within a year of the investigation were excluded

•  Other: the Ps were from an outpatient service and they were consecutively identified from the P enrollments; Ps with “on-off” phenomena (p. 498) were excluded


•  age: 36 years to 75 years

•  gender: 17m; 15f

•  vocal status: diagnosed with mild to severe voice disorders 

•  medications: All Ps were taking PD medications at the time of the investigation 

•  time since diagnosis: 1 to 18 years

–  Were the groups similar before intervention began?  NA 

  Were the communication problems adequately described? Yes 

•  disorder type:  (List) dysarthria associated with PD

•  functional level: mild to severe

5.  Was membership in groups maintained throughout the study?

•  Did the group maintain at least 80% of their original members? Yes

•  Were data from outliers removed from the study?  No 

6.   Were the groups controlled acceptably?  NA

7.  Were the outcomes measure appropriate and meaningful? Yes

•  OUTCOME #1: Acoustic measure of loudness

•  OUTCOME #2: Acoustic measure of pitch

•  OUTCOME #3: Acoustic measure of jitter 

•  OUTCOME #4: Acoustic measure of duratioN

–  NONE of the outcomes were subjective.

–  ALL of the outcome measures were objective.

8.  Were reliability measures provided?  No

  Interobserver for analyzers?  No  

•  Intraobserver for analyzers?  No  

  Treatment fidelity for clinicians?  

9.  What were the results of the statistical (inferential) testing and/or  the description of the results?

—  What level of significance was required to claim significance?  p ≤ 0.01 

•  OUTCOME #1: Acoustic measure of loudness

     – Both PLVT and LSVT increased significantly from habitual level in all tasks

•  OUTCOME #2: Acoustic measure of pitch

     – LSVT increased significantly from habitual level in all tasks

     – PLVT increased significantly from habitual level only in reciting

•  OUTCOME #3: Acoustic measure of jitter

     – Both PLVT and LSVT decreased significantly from habitual level in the vowel task

     – The difference between PLVT and LSVT is not significant

•  OUTCOME #4: Acoustic measure of duration

      – Neither PLVT nor LSVT increased significantly from habitual level

—  What the statistical tests were used to determine significance?  Place xxx after any statistical test that was used to determine significance.  

•  ANOVA: (multivariate, repeated measures) 

•  Other:  There was also a Bonferoni Correction.

  Were confidence interval (CI) provided?  No __x___

10.  What is the clinical significance?  NA

11.  Were maintenance data reported?  No 

12.  Were generalization data reported?  Yes  

13.  Describe briefly the experimental design of the investigation.

• Thirty-two adults with PD were enrolled in this investigation by researchers from the Netherlands. The site was an outpatient clinic and the patients (Ps) were identified as consecutive Ps from the clinic’s patient rolls. The single experimental session for each P lasted approximately 30 minutes.

• The experiment involved 3 tasks and 3 conditions with each task/condition pairing being produced 2 times.

     – Tasks: 

          ∞ sustaining “ah” as long as possible, 

          ∞ reciting the months of the year, 

          ∞ reading a short passage in which the same 2 sentences form the middle of the passage were selected for analysis.

     – Conditions: 

          ∞ spontaneous speaking style (“the way you speak at home,” p. 498)           

          ∞ LSVT style (“think loud, think shout,” p. 499)

          ∞ PLVT style (“speak loud and low,” p. 499)

• Initially the experimenter gave the P a verbal direction but if the P was unsuccessful, the experimenter demonstrated the targeted behavior.

• The performance of the Ps was audiotaped for later acoustic analysis.

• The results were analyzed using multivariate analysis-of-variance with repeated measures.



PURPOSE: To explore if instructing Ps with PD to “speak loud and low” limits the pitch rise associated with increased loudness.

POPULATION: Parkinson’s disease adults




DOSAGE: one, 30-minute session

MAJOR COMPONENTS: 2 interventions are briefly described: PLVT and LVST.


• The clinician (C) directs the P to produce the target speaking “loud and low” (p. 499).


• The clinician (C) directs the P to “think loud, think shout” (p. 499) when attempting to produce targets.


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