Activity Definition, Duration Estimation, and Productivity

Introduction

Construction schedules are only as reliable as the activities from which they are built. An activity is not merely a line of text such as “construct building.” It is a measurable, logically bounded piece of work that can be assigned, monitored, resourced, and linked to other work. Poorly defined activities produce ambiguous responsibilities, unrealistic durations, weak progress measurement, and unreliable completion forecasts.

Activity definition and duration estimation connect the project scope to the schedule. The estimator must translate drawings, specifications, quantities, construction methods, crew capabilities, site conditions, and contractual constraints into a time estimate. This process is partly quantitative and partly judgmental. Quantities and production rates provide a computational foundation, while productivity variation, learning, weather, access, uncertainty, and organizational performance determine whether the estimate is credible.

This chapter presents a systematic approach to defining activities, estimating durations, measuring productivity, and incorporating uncertainty into construction schedules.

Learning Objectives

By the end of this chapter, students should be able to:

1. Define activities that are measurable, assignable, and suitable for schedule control.
2. Distinguish effort, duration, production rate, and productivity.
3. Estimate activity duration from quantity, crew composition, and production rate.
4. Adjust estimates for learning, site conditions, weather, rework, and nonproductive time.
5. Use historical data and expert judgment responsibly.
6. Recognize uncertainty and distinguish estimated duration from schedule contingency.
7. Evaluate productivity data and identify ethical and managerial implications.
8. Apply these principles to develop a defensible construction activity estimate.

1. From Scope to Schedule Activities

1.1 The role of the work breakdown structure

The work breakdown structure (WBS) decomposes the project scope into progressively smaller deliverables and work packages. Activities are developed from work packages, drawings, specifications, procurement requirements, construction methods, and project constraints.

A work package describes a manageable portion of scope. An activity describes the work required to produce a measurable result within that package. For example, a work package called “reinforced-concrete frame” may contain activities such as:

• fabricate and place reinforcement;
• install formwork;
• inspect reinforcement and embedded items;
• place concrete;
• cure and protect concrete;
• strip formwork; and
• repair identified defects.

The appropriate level of detail depends on project size, reporting needs, risk, contractual requirements, and the ability to collect reliable progress data. Excessive detail creates administrative burden and false precision. Insufficient detail prevents meaningful control.

1.2 Characteristics of a well-defined activity

A useful activity normally has the following characteristics:

• A clear verb and object: “Place 120 m³ of slab concrete,” rather than “slab work.”
• A measurable scope: quantity, area, length, number, or defined milestone.
• Defined boundaries: a start condition and a finish condition.
• A responsible party: crew, subcontractor, supplier, or project function.
• Known resources: labor, equipment, materials, and temporary works.
• A logical location: floor, zone, building, grid, or workfront.
• A logical relationship: predecessor and successor activities.
• A suitable duration: long enough to control but short enough to reveal progress.
• A verifiable completion condition: inspection approval, installed quantity, test result, or accepted deliverable.

Activity names should be consistent. A practical naming convention is:

Verb + object + location + qualifier

For example: “Install 80 mm chilled-water insulation, Level 3, Zone B.”

1.3 Activity, milestone, and summary task

An activity consumes time and usually resources. A milestone represents a significant event, such as “building permit approved” or “roof watertight,” and normally has zero duration in a network schedule. A summary task groups lower-level activities and should not be used as a substitute for measurable work. Confusing summary tasks with activities can cause double counting and inaccurate resource loading.

1.4 Activity boundaries and handoffs

Activity boundaries should correspond to meaningful control points. Boundaries may be established by:

• physical location;
• trade responsibility;
• inspection or testing requirement;
• change in crew or method;
• shift or production cycle;
• material availability; or
• contractual payment measurement.

For example, “install drywall” may be divided into board installation, joint treatment, sanding, and inspection if these stages involve different crews or control points. However, splitting every minor operation into a separate activity may make the schedule difficult to maintain.

2. Fundamental Concepts and Terminology

2.1 Quantity

Quantity is the measurable amount of work. Typical units include m³ of concrete, m² of formwork, tonnes of reinforcement, metres of pipe, units of doors, or cubic metres of excavation. Quantity should be based on a defined measurement rule. For example, excavation quantity may be measured as in-place volume, while hauled material may be measured as loose volume. These are not interchangeable without an appropriate conversion.

2.2 Production rate

A production rate expresses output per unit of time. Examples include 40 m³ of concrete placed per shift or 120 m² of blockwork completed per crew-day.

2.3 Unit labor productivity

Unit labor productivity is often expressed as labor input per unit of output, such as 1.8 labor-hours per m² of formwork. This is the inverse of a production rate when the resource basis is consistent.

2.4 Effort and duration

Effort is the amount of labor or machine time required. Duration is the elapsed calendar or working time between activity start and finish. A task requiring 80 labor-hours may take two 10-hour working days with four workers, or four 10-hour days with two workers. The effort is similar, but duration differs.

A simple relationship is:

where:

• D = activity duration in working days;
• E = total labor effort in labor-hours;
• n = number of workers;
• h = scheduled hours per worker per day; and
• u = utilization factor, expressed as a decimal.

The utilization factor accounts for breaks, movement, waiting, minor interruptions, and other nonproductive time. This formula assumes that the crew can work together effectively and that increasing crew size does not create congestion or coordination losses.

2.5 Calendar time and working time

A duration estimate must state its calendar basis. “Five days” may mean five working days, five consecutive calendar days, or five shifts. Weekends, holidays, night work, restricted hours, curing periods, and weather calendars can materially change the completion date.

3. Estimating Duration from Quantity and Production Rate

The basic quantity-rate method is the most transparent starting point for duration estimation.

where:

• D = duration in the time unit used by the rate;
• Q = quantity of work; and
• R = production rate in quantity units per time unit.

The units must be compatible. If Q is 240 m³ and R is 60 m³ per shift, then D is four shifts.

The production rate may be based on a crew, a machine, a subcontractor, or an entire work system. The estimate should identify which. A rate of 60 m³ per shift is meaningless unless the estimator knows whether it refers to one placing crew, two pumps, or the complete concrete operation.

Worked Example 1: Concrete placement

A project requires 360 m³ of concrete for foundations. Historical records indicate that a crew using one pump places 45 m³ per 10-hour shift under comparable conditions. The planned work calendar provides one shift per working day.

Therefore, the planned duration is eight working days, assuming the pump, concrete supply, reinforcement, formwork, labor, testing, and access are all available. The arithmetic is straightforward, but the estimate is valid only if the historical rate is genuinely comparable.

3.1 Adjusting the nominal production rate

A nominal rate may be adjusted for site conditions. One useful representation is:

where:

• R_adj = adjusted production rate;
• R_b = baseline production rate; and
• f₁, f₂, …, f_k = dimensionless adjustment factors.

Examples include factors for restricted access, congestion, weather, supervision, material supply, crew unfamiliarity, and work-at-height conditions. Each factor should be supported by historical evidence or documented expert judgment. Multiplying many uncertain factors can create an illusion of accuracy; therefore, the estimator should record the rationale and avoid double counting.

If the baseline rate is 50 m³ per shift, restricted access reduces output to 0.85 of normal, and difficult supply logistics reduce it to 0.90, then:

For 153 m³, the duration is:

The result is exactly four shifts under the stated assumptions. In practice, the schedule may require an additional shift if setup, testing, cleanup, or uncertain supply interruptions are not included in the rate.

4. Crew Composition and Resource-Based Estimation

A crew is a coordinated group of labor and equipment that performs a production cycle. Crew composition should be based on the construction method rather than a generic labor allowance. A concrete crew, for example, may include a foreperson, placing workers, vibrator operators, finishers, survey support, pump operator, testing technician, and laborers.

The estimator should distinguish:

• direct productive labor: physically contributes to the output;
• support labor: enables production but may not be directly measured in installed quantity;
• supervision: coordinates work and quality; and
• equipment resources: plant whose capacity may limit output.

Worked Example 2: Masonry wall

A crew consists of four masons and four laborers. The planned production rate is 80 m² per crew-day. The wall quantity is 1,120 m².

Because the rate is already expressed per complete crew, the duration is 14 working days with one crew. If two equivalent crews can work independently without interference:

The approximation is valid only if there are sufficient workfronts, materials, access, supervision, and quality-control capacity. If the workfront is too narrow, two crews may obstruct one another and the rate will not double.

4.1 Crew size is not infinitely scalable

Increasing labor does not always reduce duration proportionally. Common limiting conditions include:

• restricted work area;
• crane, hoist, or pump capacity;
• limited material delivery space;
• supervisory span of control;
• safety separation requirements;
• interference between trades; and
• inspection or testing capacity.

A schedule should therefore consider crew productivity as a system property, not merely a sum of individual worker capacities.

5. Productivity Measurement and Losses

Productivity is the relationship between useful output and resource input. In construction, it is affected by design quality, planning, materials, tools, workforce skills, management, weather, access, and rework.

A general productivity expression is:

where P is productivity, O is output, and I is input. If output is measured in m² and input in labor-hours, productivity is m² per labor-hour. The reciprocal, labor-hours per m², is often called a unit labor requirement.

Measured output must be defined consistently. For example, “installed pipe” should specify whether it includes supports, testing, insulation, and accepted quality. Counting defective work as output can overstate productivity.

5.1 Productive, contributory, and non-contributory time

Field observations often classify time as:

• productive: directly transforms materials or installs work;
• contributory: supports production, such as measuring, moving tools, or reading drawings; and
• non-contributory: waiting, avoidable travel, rework, or idle time.

This classification is useful for diagnosis, but it should not be used to blame workers for conditions created by poor planning. Waiting caused by late materials, inaccessible workfaces, design changes, or unsafe conditions is a management-system issue.

5.2 Common productivity losses

Productivity losses may arise from:

• incomplete or late design information;
• material shortages or incorrect deliveries;
• equipment breakdown;
• trade interference;
• poor site layout;
• excessive crew movement;
• unclear instructions;
• inspection delays;
• weather exposure;
• rework and defects;
• labor turnover; and
• unsafe or excessively fatiguing conditions.

The estimator should avoid applying a generic “productivity factor” without identifying the causal conditions. Better practice is to model specific constraints and remove them through planning where possible.

6. Learning Effects and Repetitive Work

Workers and crews often become faster as they repeat a task. This learning effect may result from improved coordination, tool familiarity, layout optimization, and reduced decision time. It is particularly relevant to high-rise floor cycles, housing units, repetitive road sections, and modular installation.

A commonly used learning-curve model is:

where:

• T_x = time per unit for the xth unit;
• T₁ = time for the first unit;
• x = unit number; and
• b = learning exponent, normally negative when learning occurs.

If the learning rate is L, meaning that time per unit becomes L of the previous time when cumulative quantity doubles, then:

This model assumes reasonably stable methods, crews, materials, and work conditions. It should not be applied mechanically when each unit is substantially different or when the crew changes frequently.

Worked Example 3: Learning in repetitive installation

The first apartment bathroom requires 20 labor-hours. Historical evidence suggests an 85% learning rate. Thus:

The estimated labor-hours for the eighth bathroom are:

This does not mean the eighth bathroom necessarily takes exactly 11.8 hours. It is a planning estimate dependent on stable design, materials, access, and crew continuity. Learning should not be used to justify unsafe acceleration or unrealistic labor expectations.

7. Historical Data and Expert Judgment

7.1 Using historical data

Historical data are valuable when they are relevant, complete, and normalized. The estimator should examine:

• project type and scale;
• quantity and measurement rules;
• crew composition;
• equipment and method;
• location and access;
• weather and calendar;
• quality and rework levels;
• shift length; and
• whether the record represents planned or actual performance.

Data from a high-volume industrial project may not transfer directly to a congested urban renovation. Historical rates should be adjusted only after comparing the conditions that produced them.

A useful data record contains the activity code, description, quantity, unit, crew, equipment, start and finish dates, actual productive hours, interruptions, weather, and notes on unusual events.

7.2 Expert judgment

Expert judgment is necessary when the work is novel, data are sparse, or project conditions differ from historical records. A defensible judgment should identify:

1. the basis of comparison;
2. the assumptions made;
3. the principal risks;
4. the confidence level; and
5. the evidence that would cause revision.

Where several specialists are consulted, independent estimates followed by structured discussion can reduce anchoring and dominance by one individual. The final estimate should not be changed merely to meet a desired completion date.

7.3 Three-point duration estimates

When uncertainty is significant, three estimates may be developed:

• optimistic duration a;
• most likely duration m; and
• pessimistic duration b.

A beta-type weighted estimate often used in project planning is:

The formula is a planning approximation, not a law of nature. It assumes that the three-point estimates represent the same scope and calendar basis and that the most likely estimate deserves greater weight.

For a = 6, m = 8, and b = 14 working days:

The estimator should not hide the range by reporting only 8.67 days. The range communicates risk and supports management decisions.

8. Weather, Calendars, and Uncertainty

Weather affects productivity through rainfall, temperature, wind, humidity, visibility, ground conditions, and worker fatigue. It may also prevent work entirely. Weather allowances should be based on the project location, season, activity sensitivity, and historical records.

A useful distinction is:

• weather-adjusted activity duration: expected duration under the selected calendar and normal seasonal conditions;
• risk allowance: time associated with identified uncertainty; and
• schedule contingency: management reserve or time allowance held for uncertainty, depending on the project’s control system.

These should not be double counted. If a production rate already reflects average seasonal weather, adding a full weather allowance again may overstate duration.

Uncertainty can be represented through ranges, scenarios, or simulation. For example, a planner may examine normal, constrained, and severe-access scenarios. The purpose is not to create false precision but to identify activities whose completion dates are sensitive to assumptions.

8.1 Dependencies and non-working periods

Some durations are governed by elapsed time rather than active labor. Concrete curing, statutory review, testing, procurement, and manufacturer lead times may continue while labor is absent. These are often represented as lag or as separate activities, depending on the scheduling system and the need for visibility.

9. Activity Definition and Duration Estimation Workflow

A practical workflow is:

1. Review scope and documents. Examine the WBS, drawings, specifications, bill of quantities, method statements, and constraints.
2. Define the deliverable. State what will exist when the activity is complete.
3. Select activity boundaries. Use location, trade, method, inspection, or control points.
4. Measure quantity. Record unit, source, and measurement convention.
5. Select method and crew. Identify labor, equipment, materials, and workfront.
6. Obtain a baseline rate. Use comparable historical data, estimating databases, or expert judgment.
7. Adjust for conditions. Consider access, congestion, weather, learning, supply, rework, and shift pattern.
8. Calculate duration. Check units and distinguish active work from elapsed constraints.
9. Document assumptions and confidence. Record the basis, exclusions, and uncertainty range.
10. Validate with the construction team. Review constructability and resource feasibility.
11. Integrate logic and calendars. Link predecessors, successors, constraints, and non-working periods.
12. Update using actual performance. Compare planned quantity, effort, and duration with field data.

10. Illustrative Case: Estimating a Floor-Cycle Activity

The following is a fictional illustrative case for educational purposes.

Background

A contractor is scheduling a six-storey reinforced-concrete office building. Each typical floor contains 420 m² of slab formwork, 58 tonnes of reinforcement, and 210 m³ of concrete. The objective is to establish a realistic floor-cycle schedule.

Problem

The initial proposal allows ten working days per floor. The site team believes this is achievable only if formwork, reinforcement, inspection, and concrete placement are coordinated. The estimator must test the proposal rather than accept it as a target.

Analysis

Historical rates for a comparable crew are:

These activities overlap. Formwork starts first; reinforcement follows in released zones; concrete placement occurs after inspection. The nominal durations cannot simply be added because work is organized as a flow system.

The formwork rate is reduced by a 0.90 access factor because of limited crane availability:

Therefore:

The reinforcement rate is reduced by a 0.95 factor for congestion:

Thus:

Concrete placement remains three shifts, but the schedule includes one day for pre-pour inspection, testing coordination, and setup. The activity should therefore distinguish active placing from the complete ready-to-pour-to-finished sequence.

Approach and solution

The team divides the floor into two zones. Formwork releases Zone A before Zone B is complete, allowing steel fixing to begin earlier. The schedule includes:

• formwork by zone;
• reinforcement by zone;
• inspection and release;
• concrete placement;
• curing and protection; and
• stripping and handover.

The team also identifies the crane as a shared resource. A second crew is rejected because it would exceed available lifting capacity and create congestion. The ten-day target is retained only as a conditional plan, with a documented risk that crane delays or inspection slippage may extend the cycle.

Outcome

The revised schedule is more informative than a single “floor construction—10 days” activity. It exposes the controlling resources, provides measurable progress points, and permits the team to diagnose delay. The schedule baseline records the adjusted rates, assumptions, and a likely range of 10–12 working days per floor under normal conditions.

Learning points

1. A floor cycle is a production system, not one indivisible task.
2. Overlap must be supported by released workfronts and inspections.
3. Shared equipment can limit the benefit of adding labor.
4. Conditional targets should not be presented as guaranteed durations.
5. Activity definition improves both planning and later delay analysis.

11. Technology, Data, and Contemporary Practice

Estimators increasingly use digital quantity take-off, building information modelling, field data platforms, mobile time records, location-based scheduling, and automated progress measurement. These tools can improve consistency, but they do not eliminate the need for professional judgment.

Artificial intelligence and machine-learning systems may identify patterns in historical productivity or predict likely delays. Their usefulness depends on data quality, comparable project conditions, transparent assumptions, and human review. A model trained on projects with abundant labor and unrestricted access may produce misleading estimates for a constrained site.

Good governance requires version control, traceable data sources, documented model assumptions, and clear responsibility for approving the estimate. Workers should not be monitored in ways that violate privacy or encourage unsafe production behavior. Productivity measurement should support improvement, fair planning, and safe work—not punitive surveillance.

12. Common Errors and Best Practices

Common errors

• defining activities too broadly to measure progress;
• defining activities so narrowly that schedule maintenance becomes excessive;
• using rates without stating crew or equipment basis;
• mixing labor-hours, crew-days, shifts, and calendar days;
• assuming crew doubling will halve duration;
• ignoring setup, access, inspection, and cleanup;
• double counting weather or contingency;
• treating planned rates as actual performance;
• using historical data without checking comparability; and
• manipulating estimates to fit a predetermined completion date.

Best practices

• define completion criteria before estimating duration;
• use consistent quantity measurement rules;
• document assumptions, exclusions, and confidence;
• validate rates with the people who perform the work;
• separate active production from waiting and elapsed constraints;
• use location and workfront planning for repetitive construction;
• update estimates from actual field performance;
• protect workers from unsafe acceleration; and
• maintain an auditable record of changes to the baseline.

Chapter Summary

Activity definition converts project scope into manageable, measurable, and logically connected units of work. A strong activity has clear boundaries, a responsible party, identifiable resources, a measurable quantity, and a verifiable completion condition. Duration estimation commonly begins with D = Q ÷ R, but the reliability of the result depends on the definition of quantity, the basis of the production rate, crew composition, equipment, workfront, and calendar.

Productivity is affected by access, congestion, materials, design quality, supervision, weather, learning, rework, and safety conditions. Historical data are powerful when normalized and comparable; expert judgment is necessary when conditions are novel but should be documented transparently. Learning curves can assist with repetitive work, while three-point estimates communicate uncertainty better than a single deterministic number.

A professional schedule distinguishes effort from elapsed duration, recognizes resource limits, avoids double counting allowances, and is updated using actual performance. Technology can strengthen estimating and monitoring, but ethical governance, data quality, and human judgment remain essential.

Key Terms

Activity: A defined piece of work that consumes time and may use resources.

Activity boundary: The stated start and finish conditions of an activity.

Baseline production rate: The output rate used before project-specific adjustments.

Calendar: The working-time rules governing shifts, holidays, weekends, and restrictions.

Crew: A coordinated group of workers and equipment performing a production operation.

Duration: Elapsed working or calendar time required to complete an activity.

Effort: Quantity of labor or machine time required to perform work.

Learning curve: A model describing improved unit performance through repetition.

Milestone: A significant event or control point, normally with zero duration.

Non-contributory time: Time that does not directly or supportively advance production.

Production rate: Output quantity produced per unit of time.

Productivity: Output achieved relative to resource input.

Quantity: Measurable amount of work included in an activity.

Rework: Repetition or correction of work because it was defective or incomplete.

Risk allowance: Time or resources associated with identified uncertainty.

Summary task: A grouping of subordinate schedule activities.

Three-point estimate: An estimate using optimistic, most likely, and pessimistic values.

Utilization factor: The proportion of scheduled time effectively available for production.

Work package: A manageable component of the work breakdown structure.

Workfront: The physical area released and available for a crew to perform work.

Review Questions

Short Answer Questions

1. What characteristics distinguish a well-defined construction activity from a vague task description?
2. Explain the difference between effort and duration.
3. Why might doubling the crew fail to halve an activity’s duration?
4. What information should be recorded when using historical production data?
5. Distinguish weather-adjusted duration from schedule contingency.

Long Answer Questions

1. Explain how a work breakdown structure is transformed into measurable schedule activities. Include the importance of boundaries, quantities, responsibility, and completion criteria.
2. Discuss the quantity-rate method of duration estimation and explain the assumptions required for its valid application.
3. Describe the principal causes of construction productivity loss and explain how a planner can diagnose and reduce them.
4. Explain the use of learning curves in repetitive construction. Discuss their assumptions and limitations.
5. Compare historical data and expert judgment as sources of duration estimates. How should a professional combine and document them?

Analytical / Application Questions

1. A crew must install 1,800 m² of wall panels at a baseline rate of 150 m² per day. Restricted access has a factor of 0.80, and material deliveries have a factor of 0.90. Calculate the adjusted rate and duration, then identify two assumptions that should be validated in the field.
2. A concrete activity has optimistic, most likely, and pessimistic durations of 5, 8, and 17 working days. Calculate the weighted three-point estimate and explain why reporting only the weighted value may be misleading.
3. A project manager proposes adding a second installation crew to reduce a 12-day activity to 6 days. Analyze the proposal using workfront availability, equipment capacity, supervision, safety, and productivity considerations. Recommend the information needed before approving the change.

Multiple Choice Questions with Answers

Question 1

Which characteristic is most important for a measurable schedule activity?

A. It has a broad and general description.

B. It has a defined quantity and completion condition.

C. It has the longest possible duration.

D. It excludes responsibility for resources.

Correct Answer: B. It has a defined quantity and completion condition.

Question 2

A crew places 240 m³ of concrete at 60 m³ per shift. What is the nominal duration?

A. 2 shifts

B. 3 shifts

C. 4 shifts

D. 5 shifts

Correct Answer: C. 4 shifts

Question 3

What is the principal difference between effort and duration?

A. Effort is elapsed calendar time, while duration is labor input.

B. Effort is resource time, while duration is elapsed time.

C. Effort and duration always have identical values.

D. Duration applies only to equipment.

Correct Answer: B. Effort is resource time, while duration is elapsed time.

Question 4

A baseline production rate is 50 m³ per shift. Access and logistics factors are 0.85 and 0.90. What is the adjusted rate?

A. 38.25 m³ per shift

B. 40.00 m³ per shift

C. 45.00 m³ per shift

D. 53.00 m³ per shift

Correct Answer: A. 38.25 m³ per shift

Question 5

Which condition most directly limits the benefit of adding a second crew?

A. Independent workfronts are available.

B. Materials are delivered reliably.

C. The work area is congested and shared equipment is limited.

D. Supervision and inspection capacity are increased.

Correct Answer: C. The work area is congested and shared equipment is limited.

Question 6

In a learning-curve model, a negative exponent generally indicates that:

A. Unit time increases with repetition.

B. Unit time decreases with repetition.

C. Quantity is measured incorrectly.

D. Weather has no effect on production.

Correct Answer: B. Unit time decreases with repetition.

Question 7

For optimistic duration 6 days, most likely duration 8 days, and pessimistic duration 14 days, the weighted three-point estimate is approximately:

A. 7.00 days

B. 8.00 days

C. 8.67 days

D. 10.00 days

Correct Answer: C. 8.67 days

Question 8

Which practice best supports responsible use of historical productivity data?

A. Use the highest rate ever achieved on any project.

B. Transfer rates without checking project conditions.

C. Normalize the data for method, crew, access, and measurement rules.

D. Ignore interruptions because they reduce the apparent rate.

Correct Answer: C. Normalize the data for method, crew, access, and measurement rules.

Question 9

What is a milestone in a network schedule?

A. A resource-consuming activity with a variable crew.

B. A significant event or control point, normally with zero duration.

C. A summary task containing all project work.

D. A production rate adjustment factor.

Correct Answer: B. A significant event or control point, normally with zero duration.

Question 10

Why should productivity measurement not be used simply as punitive worker surveillance?

A. Productivity is unaffected by management conditions.

B. It can ignore system causes and encourage unsafe behavior.

C. Workers never influence production.

D. Historical data are always more accurate than field data.

Correct Answer: B. It can ignore system causes and encourage unsafe behavior.