Find an exact binomial probability

Calculate the chance of a specified count in independent trials.

Guides · Basic statistics · 3 min read

Example: exactly two nonconforming labels

Inspect 25 labels. Assume each has a 4% chance of nonconformance, independently of the others.

Download the scenario reference (CSV)

This is the same example used in Help. The CSV lists reference scenarios. Enter the selected scenario manually on Inputs; importing it does not configure this calculator. Use Open example in a practice copy in Help to prefill the inputs.

1. Create the workspace

In the sidebar, open Basic Statistics and choose Distributions. Create an analysis, name it, select New blank worksheet, then choose Create analysis.

2. Choose the calculation

On Inputs, choose Discrete for Distribution type, Binomial for Distribution, then Probability mass (PMF) for Calculation.

3. Enter the model

Enter 25 in Number of trials (n) and 0.04 in Success probability (p). Here a “success” means finding a nonconforming label.

4. Enter the question

Choose Single value for Value source. Enter 2 in Value (x). No worksheet columns are assigned.

Distributions: Inputs with the example’s assignments and settings
Inputs with the selected distribution, calculation, model parameters and question. View full-size image (opens in a new tab)

5. Run analysis

Choose Run analysis, then open Results.

6. Interpret results

  1. Check the question

    Inspect 25 labels. Assume each has a 4% chance of nonconformance, independently of the others.

  2. Read the calculated value

    The PMF is 0.187707, about 18.77%. Under this model, that is the chance of finding exactly two nonconforming labels among 25.

  3. Understand what it means

    Exactly two excludes counts of zero or one. For at most two, use the cumulative probability instead.

  4. Use the model carefully

    Check whether the same nonconformance probability and independence are reasonable for the labels being sampled. Batch clustering can make this model inappropriate.

More details: read each result section

Complete result tables use six significant digits, as in Help.

Distribution values

x is the count requested. PMF is P(X = x), the probability of exactly that count. Exactly two excludes counts of zero or one. For at most two, use the cumulative probability instead.

Distribution values · 1 row
xPMF
20.187707

Distribution summary

Type distinguishes continuous values from whole-number counts. Distribution names the model. Calculation records PMF (exact-count probability), PDF (density), CDF (cumulative probability) or ICDF (quantile). The remaining rows record the active parameters; they are assumptions entered on Inputs.

Distribution summary · 5 rows
SettingValue
TypeDiscrete
DistributionBinomial
CalculationPMF
Number of trials (n)25
Success probability (p)0.04
  • Binomial(n=25, p=0.04)

7. Create a report

Keep Distribution values (or the quantile table) and Distribution summary. State the model assumptions, time unit or count interval, and the question being answered. Exactly two excludes counts of zero or one. For at most two, use the cumulative probability instead.

Choose Add to report from the completed run. Open Choose individual items and advanced options to select tables and charts, then choose Add to draft. Hidden items stay in the saved analysis.

Name the report and add the purpose of the study and your interpretation. Choose Save, review Preview, then use Export → Download HTML. The example below contains the full selected content, including results beyond one screen.

Complete native output for this Help example, including applicable tables, charts and run notes. Report numbers use the app’s displayed precision. Exported charts are static. On narrow screens, scroll wide charts and tables sideways.
View example report: Exactly 2 nonconforming labels in a 25-label sample

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