Professional Guide
Professional & Research Guides
Practical professional guides that explain the methods behind the calculators — research and statistics, workforce and operations, quality, business and finance, time and productivity, HR, and data analysis — and link straight to the tools that implement them.
Research & Statistics
How to Choose the Right Statistical Test
A practical framework for picking the right statistical test: start from your research question, data type and study design, then check the assumptions.
Sample Size and Margin of Error: A Practical Guide
How sample size controls margin of error, the formulas behind both, the finite-population correction, and the practical caveats researchers should not skip.
Understanding P-Values and Statistical Significance
What a p-value actually means, what it does not mean, the role of the significance level, and why the field is moving away from the 0.05 bright line.
Confidence Intervals Explained
What a confidence interval is, how to interpret the 95% level correctly, how to calculate one for a mean or a proportion, and what changes its width.
Correlation vs Regression
The difference between measuring a linear association (correlation) and modelling a relationship to make predictions (regression), and how R² connects them.
T-Test vs Z-Test vs ANOVA
When to use a z-test, a t-test or an ANOVA, the assumptions behind each, and how the tests relate — including why F equals t² for two groups.
How to Calculate NPS
The Net Promoter Score formula, how to classify promoters, passives and detractors, a worked example, and the caveats about small samples and timing.
Survey Research Statistics: A Practical Guide
The core statistics every survey researcher should understand — response, completion and incidence rates, sample size, margin of error and significance — and how they fit together.
Effect Size and Statistical Power: Designing Studies That Can Detect Effects
Why statistical significance is not enough — how to measure effect size with Cohen's d and design studies with adequate statistical power before you collect data.
Workforce & Operations
Workforce Capacity and Utilization: A Practical Guide
How to measure available capacity, the utilization rate and productivity, and how to use them to decide whether you have enough people to meet demand.
FTE and Staffing Requirements: How Many People Do You Need?
Full-time equivalents, staffing ratios, shift coverage and headcount planning — how to translate workload into the right number of people.
SLA Compliance and Turnaround Time: Service Levels That Hold
How to measure service-level agreement compliance, on-time delivery, turnaround time and cycle time — and use the numbers to keep promises you can keep.
Erlang C and Call-Centre Staffing: How Many Agents Do You Need?
The Erlang C formula for staffing a service desk or call centre to a target answer time, with the assumptions, limits, and how queue abandonment fits in.
Quality & Compliance
Measuring Process Quality: DPMO, First Pass Yield and Rework
How to quantify process quality with defects per million opportunities, first-pass yield and rework rate — and how a quality scorecard ties them together.
Process Capability (Cp/Cpk) Explained
How to judge whether a process can meet its specification: capability indices, what Cpk < 1 means, and how capability differs from simply being in control.
AQL Sampling and Audit Sample Size: How Many to Inspect
Acceptable quality limits, sampling plans and audit sample sizing — how to decide how many units to inspect or records to audit to make a defensible decision.
Business & Finance
ROI, CAGR and Break-Even: A Finance Guide for Non-Finance Professionals
How to evaluate an investment with return on investment, compound annual growth rate and break-even analysis — the three numbers that make a business case credible.
Profit Margin, Markup and Budget Variance: Pricing and Control
The difference between margin and markup, why the confusion is expensive, and how budget variance turns planned numbers into a control tool.
Time & Productivity
Planning Across Time Zones: Distributed Teams Done Well
How to convert times, find overlapping working hours, and cost the meetings you schedule across time zones — so distributed teams work, not just talk.
Estimating Work Hours and Project Timelines
How to estimate work and billable hours, build a realistic project timeline, work back from a deadline, and budget focused time — without the usual optimism bias.
HR & People Operations
Measuring Employee Turnover and Its Cost
How to calculate turnover rate, time-to-fill and the true cost of losing a hire — the numbers that make retention a business case, not a feeling.
Workforce Planning: Headcount, Span of Control and Compensation
How to plan headcount, use compa-ratio for pay equity, size span of control, and measure workforce diversity and employee experience with eNPS.