Co-author: Mariel Solomon, MS, CCC-SLP


If the last few months have taught us anything, it’s that the only constant is change. New diagnoses, new policies and procedures, and rapidly evolving research mean that best practices one day may no longer be best practices a short time later (Namasivayam-McDonald & Riquelme, 2020). How are busy practicing clinicians supposed to keep up?

 ASHA’s National Center for Evidence-Based Practice is here to help you keep pace with the latest dysphagia research and make the best treatment decisions for your clients. We’ve streamlined the EBP process with our updated resources and a new EBP toolkit. One key component of EBP is external scientific evidence.

Primary Research

Primary research refers to individual studies attempting to answer a specific research question using raw data collected by the researcher(s). In experimental studies, the investigator manipulates one or more variables to compare those that received the manipulated condition to those that did not. In qualitative and observational/non-experimental studies, although there is no experimental manipulation, they may involve a comparison group. 

Primary research can be conducted 

  • retrospectively (i.e., researchers collect data on the study participants’ past) or 
  • prospectively (i.e., researchers follow study participants over time and collect data to capture change). 

Here are some common types of study designs:

Experimental Study Designs 

  • Randomized controlled trial (RCT) – Participants are randomly assigned to either the control group or an experimental group. Researchers compare outcomes from each group to determine whether the intervention caused any change.
    • Controlled trial – A study involving non-randomized groups (i.e., experimental, comparison/control), which helps determine the effects of the intervention.
  • Single-subject designs – Also known as single-case experimental designs, this type of experimental design allows researchers to closely examine specific changes in each participant. Each participant serves as their own control (i.e., compared to themselves) and researchers measure the outcome or dependent variable repeatedly across phases (e.g., baseline phase, intervention phase, withdraw phase). There are many variations of a single-subject design study.
  • Cross-over trial – This is a study in which participants first receive one type of treatment and then researchers switch them to a different type of treatment.

Observational/Non-Experimental Study Designs

  • Cohort – A cohort is an observational design study, possibly including a control group, in which researchers follow participants over time to determine the factors leading to different outcomes. Cohort studies can be retrospective or prospective.
  • Case–control – This retrospective, observational study identifies an outcome of interest and compares a sample of people with that outcome (case) and a sample of people without that outcome (control). This design enables researchers to determine possible differences of previous exposures, experiences, and risk factors—any of which could explain their different outcomes. 
  • Cross-sectional – This is a study of a single sample at one point in time to understand the relationships among variables in the sample.
  • Case study – A case study is an uncontrolled, observational study of events and outcomes in a single case.
    • Case series – A description of uncontrolled, non-experimental events and outcomes for a series of similar cases who receive the same intervention or have the same outcome.

The chart below can help you better understand the features of the study designs commonly seen in audiology and speech-language pathology research.

Secondary Research

Secondary research, also called synthesized research, combines the findings from primary research studies and provides conclusions about that body of evidence. Below are three common types of synthesized research, which are also found on the ASHA Evidence Maps.

Systematic Reviews

Systematic reviews use systematic methods to search for and compile a body of evidence to answer a research or clinical question about the efficacy/effectiveness of an assessment or treatment approach. Typically, studies included in a systematic review have met predetermined eligibility and quality criteria (e.g., studies must be experimental designs). The systematic review then provides qualitative conclusions based on the included studies.

Well-done systematic reviews offer greater transparency because they provide details about their inclusion/exclusion process. They also typically assess each study for its methodological quality and level of evidence. Using transparent methods reduces bias and increases the confidence of the findings and conclusions of the research. Systematic reviews can provide a synopsis of the state of the evidence about a given clinical topic.


Meta-analyses use systematic and statistical methods to answer a research or clinical question about a specific assessment or treatment approach. Like systematic reviews, included primary studies must meet predetermined eligibility and quality criteria. The meta-analyses provide quantitative conclusions (e.g., pooled effect size, confidence interval) to determine the overall treatment effect or effect size across studies. The additional statistical measures can provide a better picture of the clinical significance.

Clinical Practice Guidelines

Clinical practice guidelines are systematically developed statements created by a group of subject matter experts to provide a comprehensive overview of a disorder, detail the benefits and harms of specific assessment and treatment approaches, and optimize delivery of services. Guidelines grade recommendations based on the quality and amount of available evidence and classify them as either of the following two types of recommendations:

  • Evidence-based recommendations: A systematic review of the evidence informs the group of experts and their recommendations.
  • Consensus-based recommendations: These recommendations are based on a summary of expert opinions.


When looking for research, it’s important to consider what question you’re trying to answer in order to choose the best research design.

Consider the study designs below to answer your clinical question most effectively.

If you need to: assess accuracy in differentiating clients with or without a specific condition.

You want to ask: Screening/Diagnosis

For example: Is the Toronto Bedside Swallowing Screening Test or the 3 oz water swallow test more accurate in identifying patients with dysphagia following stroke?

Preferred study designs: Prospective, blind comparison to reference standard; cross-sectional also works 

If you need to: determine the efficacy of an intervention

You want to ask: Treatment/Service Delivery

For example: What is the most effective treatment to improve labial seal in adults with oral dysphagia? 

Preferred study designs: Randomized controlled trial (RCT); controlled trial (non-randomized) and single-subject/single-case experimental design also work

If you need to: identify causes or risk factors of a condition or predict the client’s likelihood of outcomes over time due to factors other than intervention.

You want to ask: Etiology/Prognosis 

For example: What are the risk factors for dysphagia? What is the prognosis of an individual with multiple sclerosis? 

Preferred study design: Cohort; case–control Case series also work 

If you need to: obtain and assess clients’ opinions and experiences

You want to ask: Quality of Life/Perspective 

For example: How do patients feel about modified diets? 

Preferred study design: Qualitative studies (e.g., case study, case series)

If you need to: compare cost of treatments, tests, and other factors due to the disorder.

You want to ask: Cost 

For example: What is the cost of care for individuals with dysphagia requiring a feeding tube compared to those requiring diet modification? 

Preferred study design: Economic analysis

If you need to: identify factors to reduce likelihood of a disorder.

You want to ask: Prevention 

For example: What are some strategies to prevent aspiration pneumonia? 

Preferred study design: randomized control trial; controlled trial (non-randomized), cohort, and case-control also work 


Finding the right study type for your clinical question helps ensure that you find what you are looking for. External scientific evidence combined with client data, your own clinical expertise and your client’s perspective ensure that your clinical decision is one that you can feel confident in (Higginbotham & Satchidanand, 2019). Our resources are here to help you every step of the way.


Namasivayam-MacDonald, A. & Riquelme, L. (2020). Speech-Language Pathology Management for Adults With COVID-19 in the Acute Hospital Setting: Initial Recommendations to Guide Clinical Practice American Journal of Speech-Language Pathology.

Higginbotham, J. & Satchidanand, A. (2019). From Triangle to Diamond: Recognizing and Using Data to Inform Our Evidence-Based Practice. ASHA Journals Academy. Retrieved July 29, 2020 from

Co-author Bio

Mariel Solomon, MS, CCC-SLP, is a clinical research associate for ASHA’s National Center for Evidence-Based Practice in Communication Disorders (N-CEP), where she focuses on pediatric speech-language pathology topics for resources such as the ASHA Evidence Maps. Prior to working at ASHA, she was a clinician in a variety of school settings ranging from early intervention to post-secondary education services.