Stuttering Formulas and Calculations
What are the stuttering formulas? How on earth do you calculate them? What does it all mean?
This article is here to help you through it all. But, if you want the quick, down and dirty way, you can input your sample data and have it calculated for you using this stuttering calculation spreadsheet (it’s basically a stuttering calculator, so you can avoid ever having to do a stuttering calculation like the ones listed below ever again). It has a video to tell you how to use it. It even tells you information about the numbers it calculates for you to allow for an easier overall evaluation translation that I talk about below. Want it to be even easier? Get the stutter assessment bundle here.
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The formulas:
- Weighted SLD Severity: [(How many word/syllable/sound repetitions occurred) x (avg # of repetitions per repetition occurrence)] + [(Blocks+Prolongations) x (avg duration length of blocks and prolongations)] → 4–9.99 = Mild Stutter, 10–29.99 = Moderate Stutter, and ≥30 = Severe Stutter (Ambrose and Yairi, 1999)
- Stuttering-Like Disfluency % (SLD%): [(How many word/syllable/sound repetitions happened) + (How many blocks and prolongations)] / (Number of words in the sample) → Typically individuals who stutter have 3% or more; Fluent individuals produce 2% or less (Tumanova et al., 2014)
- NONStuttering-Like Disfluency % (NSLD%): (Number of NONstuttering-like disfluencies: interjections/phrase repetitions/revisions) / (Number of words in the sample) → Even though these are considered “normal,” people who stutter can use these to try to “cover up” their stutter, so be on the lookout for higher usage of these.
- Total Disfluency % (TD%): [(How many word/syllable/sound repetitions occurred) + (How many blocks and prolongations) + (Number of NONstuttering-like disfluencies: interjections/phrase repetitions/revisions)] / (Number of words in the sample) → Usually 8% or more categorizes a person as someone who stutters (Tumanova et al., 2014).
- Stuttering-Like Disfluencies Compared to ALL disfluencies (SLD/TD):[(How many word/syllable/sound repetitions occurred) + (How many blocks and prolongations)] / [(How many word/syllable/sound repetitions occurred) + (How many blocks and prolongations) + (Number of NONstuttering-like disfluencies: interjections/phrase repetitions/revisions)] → Usually 65% or more categorizes a person as someone who stutters (Yairi & Ambrose, 1999)
- Average Duration Length of Blocks/Prolongations: (Add up all of the duration lengths; 1=brief, 2=noticeable, 3=distracting)/ (Number of blocks and prolongations) → You’ll need this for your Weighted SLD Severity Rating
- Average # of Reps per Repetition Stutter Type Occurrence: (Add up all of the repetition numbers — ex: “B-b-b-ball, m-m-mom” would be 3+2) / (Number of time a repetition occurred — ex: “B-b-b-ball, m-m-mom” would be 1+1) → You’ll need this for your Weighted SLD Severity Rating
- Ratio of Disfluencies (RDF) NDF/SDF: (NONstuttering-like disfluencies: interjections/phrase repetitions/revisions) / [(Number of blocks and prolongations)+(Number of Word/Syllable/Sound Repetitions) → <1 indicates stuttering, 1–3 indicates cluttering-stuttering, 3+ indicates cluttering (Van Zaalen-Op ‘t Hof et al., 2009)
- Sound Prolongation Index (SPI%): (Number of blocks and prolongations)/ [(How many word/syllable/sound repetitions occurred) + (How many blocks and prolongations) + (Number of NONstuttering-like disfluencies: interjections/phrase repetitions/revisions)] → Usually higher SPI% = more severe stutter (Schwartz & Conture, 1988)
- Number of Sound/Syllable/Word Repetitions: Count all of these→ You’ll need this count to help you figure out some of the above calculations.
- Number of Blocks/Prolongations (B & P): Count all of these→ You’ll need this count to help you figure out some of the above calculations.
- Number of NONStuttering-Like Disfluencies: Count all of these→ You’ll need this count to help you figure out some of the above calculations.
- Approx. Average # of Syllables Per Minute: (Number of Words in Sample/Minutes it Took to Complete Sample)*1.5 → It is timed by 1.5 because it is approximating on average each word has about 1.5 syllables in the sample. Lower syllable avg per minute compared to peers can = longer stutters, which can = more severe stutter (Furquim de Andrade et al., 2003)
My hope is that this information empowers you to complete your next stuttering evaluation. To make it simpler, use 100 word samples. Again, if you want to take the easy road out, here is a bundle to help you elicit 100 word samples and calculate the data for them.
