# Effort is not duration: when adding people helps > Why ten days of review don't become two with five reviewers: the parts that can't be split, the cost of coordinating, and the waiting no extra person removes. - Course: [Project Management Without the Bureaucracy: Run One Project from Brief to Closure](https://productovi.com/courses/project-management-without-bureaucracy.md) - Module: Time: dependencies and the critical path - Lesson 11/32, ~24 min - Source: https://productovi.com/courses/project-management-without-bureaucracy/effort-is-not-duration ## Five reviewers, two days? **Leo:** Vira's review is on the critical path and takes ten days. I know five physics teachers. Five reviewers, two days, problem solved. **Vira:** It doesn't work like that. **Alex Tutor:** Leo just divided **effort** by people. Effort is the amount of work, in person-days. **Duration** is the calendar time from start to finish, including waiting, briefing and the parts only one person can do. **Alex Tutor:** Duration is never simply effort divided by the number of people. Let's see why on the review itself. > **Exercise:** **True or false:** a review that takes one person 10 days takes five people 2 days. ## What the review is made of > **The review, part by part** > > Vira's review of the five units, as she describes it: > > - **8 days that can be split:** reading and checking the units, about 1.6 days per unit. > - **2 days that can't:** Vira's final pass across all five units, checking that terms, notation and difficulty line up. > - **1 day per extra reviewer:** briefing them and agreeing what counts as an error, before they start. > > Duration with *n* reviewers = 8 ÷ *n* + 2 + (*n* − 1) × 1. **Vira:** Reading units can be shared. The final pass can't: someone has to hold all five in one head, and that someone is me. **Alex Tutor:** And each new reviewer costs a day before they help: briefing, agreeing what counts as an error. Otherwise you get five different standards to reconcile. **Danylo:** Same in my world. Two developers on one feature spend the first day agreeing how it should work. **Sofia:** So with one more reviewer: 8 split in two is 4, plus Vira's 2, plus 1 day of briefing. **Alex Tutor:** Before you answer, notice that Vira's 2 days stay the same however many reviewers join. That part sets a floor no headcount can go below. > **Exercise:** Using the review formula, 8 ÷ n + 2 + (n − 1) × 1, how many days does the review take with **two** reviewers? ## And with five? **Alex Tutor:** Seven days instead of ten: three days off the critical path. Now Leo's five. **Sofia:** 8 divided by 5, plus Vira's 2, plus 4 days of briefing for four extra people. **Leo:** That can't be slower than two reviewers. **Alex Tutor:** Check it. The part you can split keeps shrinking, but the parts you can't split stay, and coordination grows with every person. > **Exercise:** And with **five** reviewers, as Leo suggested? In days, to one decimal place. **Alex Tutor:** Why does coordination grow so fast? Count the pairs. > **Exercise:** Coordination grows with group size because every pair of people may need to agree. How many pairs are there in a group of **5** reviewers? ## Effort goes up **Hanna:** And what do I pay for? Two reviewers mean more person-days, not fewer. **Alex Tutor:** Count it before Hanna does. > **Exercise:** With two reviewers the review takes 7 calendar days: 8 splittable days, Vira's 2-day final pass, and a briefing day for each of the two. How many **person-days of effort** is that? **Alex Tutor:** Right. With two, the effort is 8 + 2 plus a briefing day for each of them: 12 person-days for 7 calendar days. You buy calendar time with extra effort. **Alex Tutor:** That's worth it only on the critical path. Three days saved on a task with float buys nothing. **Vira:** One extra reviewer I can live with. Someone I know, briefed by me, early in the review. **Hanna:** Then I'll plan 8,000 UAH for them, as our own assumption, from the 154,550 we have left. > **Exercise:** When is adding a person to a task likely to shorten the schedule? Select all that apply. ## Waiting doesn't split **Danylo:** Roman's screening shows 9 days of effort but 18 days of duration. Is he slow? **Alex Tutor:** No. Candidates take days to reply, and they're free only evenings and weekends. Half of that duration is waiting. **Sofia:** So a second recruiter would mostly wait twice. **Alex Tutor:** Mostly. Waiting shrinks by starting earlier or asking differently, not by adding people. **Vira:** Roman already asks candidates for their free slots in the first call. That saved him a round of messages. **Alex Tutor:** Danylo's question has a general answer. Pick it. > **Exercise:** Roman's screening is 9 person-days of effort but takes 18 days: candidates take days to reply and are free only evenings and weekends. What best shortens that kind of duration? **Alex Tutor:** So before adding anyone, ask four questions. Is the task on the critical path? Can its work really be split? Who briefs the newcomer, and is that person critical too? Is the duration work or waiting? **Leo:** And if every answer says no? **Alex Tutor:** Then change the plan, not the headcount: start something earlier, run it in parallel, or cut scope on the critical path. **Sofia:** That's the case next: all seventeen tasks, and the real date. > **Exercise:** Which question should you ask **first** before adding a person to any task? **Alex Tutor:** Leo still wants more recruiters. Use the four questions in your reply. > **Exercise:** Leo proposes giving Roman two more recruiters "to cut sourcing from 18 days to 6". Its effort is 9 person-days and it has float. Reply to Leo in three or four sentences. > **Key ideas** > > - **Effort** is work in person-days; **duration** is calendar time, including waiting, briefing and parts only one person can do. Duration is never simply effort ÷ people. > - The review: 8 splittable days + 2 days only Vira can do + 1 day per extra reviewer. One reviewer: 10 days; two: 7; five: 7.6, slower than two. > - Extra people raise effort (12 person-days for 7 calendar days with two reviewers): buy calendar time only on the critical path. > - Waiting (candidates replying) doesn't split; start earlier instead. > - Before adding anyone: critical? splittable? who briefs them? work or waiting? - Previous lesson: [The critical path and float](https://productovi.com/courses/project-management-without-bureaucracy/critical-path-and-float.md) - Next lesson: [Case: the schedule to 1 February](https://productovi.com/courses/project-management-without-bureaucracy/schedule-to-a-fixed-date-case.md) --- Productovi Learning. Free, no sign-up needed to read.