Decision Making
Purchase Task
Also called: hypothetical purchase task, commodity purchase task, behavioral economic demand task
Measure how demand changes with price, with hypothetical quantities, peak spending and an exponentiated demand curve.
4-6 minUntimed
Free to start: 10 free participants per account, then $0.99 per participant for academic research, or any yearly plan. Try it here first, with no account.
- Papers, 2021 to 2025
- 178
- Evidence grade
- C
- Registered clinical studies
- 89
What it measures
Measures how demand changes with price. Adults report how many units of one commodity they would buy for a day at 16 rising prices. Reports demand elasticity, intensity, breakpoint and peak spending. All purchases are hypothetical.
Constructs
- Behavioral economic demand
- Price sensitivity
- Commodity valuation
Research uses
- Behavioral economics research
- Consumer decision research
How the paradigm works
The Purchase Task measures how quantity demanded changes with price. Adults imagine buying and using one commodity over 24 hours with their usual budget. They report quantities at 16 ascending prices, including free, for snack food, alcohol, cigarettes or e-cigarettes. Each price is a separate purchase; nothing is bought. A comprehension question and number-entry practice come first.
Scores
- Demand Elasticityscore
- Alpha from the exponentiated demand curve, fitted in original quantity units including zeros. Its scale depends on commodity units, currency and fixed k.
- Larger alpha means demand falls more rapidly with price; compare the same units and k
- Demand Intensitycount
- Reported units at zero price.
- Unconstrained quantity in this scenario
- Breakpointstudy currency
- First price with zero units; null when no zero is observed or the series is incomplete.
- Price per commodity unit
- Maximum Spendingstudy currency
- Largest observed price times quantity over the complete price series.
- Peak hypothetical spending
- Price at Maximum Spendingstudy currency
- Lowest price at the observed spending maximum; null when all spending is zero.
- Price per commodity unit
- Fitted Intensitycount
- Q0 estimated by the demand curve, distinct from the free-price answer.
- Model estimate of unconstrained quantity
- Demand Fit R²score
- Variance explained by the fitted curve; null when no identifiable decreasing fit is available.
- Describes fit to these answers
- Demand Fit Availableflag
- 1 for an identifiable fit to the complete series, otherwise 0.
- Check before comparing fitted parameters
- Demand Trendscore
- Log10 quantity decrease divided by log10 price span, adding 0.01 to quantities and prices.
- Below 0.025 is flagged
- Demand Bounce%
- Share of price increments where quantity rises by more than 25% of the initial quantity plus 0.01.
- Above 0.10 is flagged
- Trend Flagflag
- 1 when trend is below 0.025. All-zero demand is retained.
- Review within the study
- Bounce Flagflag
- 1 when more than 10% of price steps have a large upward jump.
- Review within the study
- Reversal Flagflag
- 1 when positive purchasing follows at least two consecutive zero answers.
- Review within the study
- Zero Demandflag
- 1 when every price has an explicit zero answer in a complete run.
- A valid reported preference, not a missing response
- Prices Answeredcount
- Prices with a usable integer quantity and response time of at least 100 ms.
- 16 in a complete run
- Comprehension Correctflag
- Whether the participant correctly said each price is a separate purchase.
- Describes understanding of the instructions
- Median Decision Timems
- Median time to enter and confirm a usable quantity.
- Descriptive; no deadline
- Anticipationscount
- Quantity answers made in under 100 ms, omitted from demand indices.
- Describes response timing
Use and evidence
178 papers from 2021 to 2025 name this task in their title or abstract, up 1% compared with 2016 to 2020. That ranks it 166 of 582 test families in our census. See the counts for every test.
Show the numbers
| Year | Papers |
|---|---|
| 2025 | 46 |
| 2024 | 26 |
| 2023 | 24 |
| 2022 | 54 |
| 2021 | 28 |
| 2020 | 43 |
| 2019 | 39 |
| 2018 | 29 |
| 2017 | 33 |
| 2016 | 32 |
| 2015 | 19 |
| 2014 | 17 |
| 2013 | 8 |
| 2012 | 13 |
| 2011 | 3 |
| 2010 | 6 |
| 2009 | 3 |
| 2008 | 3 |
| 2007 | 1 |
| 2006 | 3 |
| 2005 | 0 |
| 2004 | 2 |
| 2003 | 0 |
| 2002 | 0 |
| 2001 | 1 |
| 2000 | 0 |
Use grade C
100 to 299 papers from 2021 to 2025.
Evidence grade C
At least 2 test-retest papers, 30 reliability or validity papers or 3 registered clinical studies.
- Papers on test-retest reliability
- 7
- Papers on reliability or validity
- 100
- Registered clinical studies using it as an outcome
- 89
Measured on ConductCognition
Pooled across the studies that feed our platform norms, by device group. A figure needs 50 or more people.
No pooled figure yet.
Note on the counts: Original hypothetical purchases; adults only; four commodities; study currency; observed demand indices and exponentiated fit; no diagnostic claim..
How the grades work
Use: A is 1,000 or more papers from 2021 to 2025, B 300 to 999, C 100 to 299, D 30 to 99 and E fewer than 30. Evidence: A means at least 25 papers report its test-retest reliability and at least 25 registered clinical studies use it as an outcome; B, at least 8 test-retest papers, and either 5 registered clinical studies or 150 reliability or validity papers; C, at least 2 test-retest papers, 30 reliability or validity papers or 3 registered clinical studies; D, little published measurement evidence found. The counts measure use. They include every paper that names the task in its title or abstract. Grades describe the published research on this task, not ConductCognition's version of it.
Source: ConductCognition test census 0.39.0, counted 10 November 2026 from OpenAlex and ClinicalTrials.gov.
Task design
The trial sequence as the test runs in ConductCognition.
- Purchases
- 16 ascending prices from 0 to 100 by default, multiplied by 0.1, 1, 10 or 100 in settings. Quantities are whole units from 0 to 999. All prices are answered, even after zero demand.
- Commodity
- Snack food (30 g portions), alcohol (standard drinks of 10, 12 or 14 g alcohol), cigarettes (one cigarette) or e-cigarettes (10 puffs). Participants imagine their usual preferred product.
- Scenario
- One day, 24 hours, with the usual budget, no existing supply or other source, no sharing or saving. Each price is an independent hypothetical purchase. Nothing is bought.
- Eligibility
- Adults aged 18 or older only. An age confirmation precedes the questions; under-18 participants leave the task.
- Practice
- One comprehension question with feedback and one number-entry practice. No time limit.
- Curve
- Exponentiated demand equation with zeros retained, fitted by least squares including the free-price answer. k is 3 by default, 1 to 5 in settings. Keep currency, units and k the same for comparisons.
- Scores
- Observed intensity, first zero-demand price, maximum spending (Omax), its lowest tied price (Pmax), fitted intensity, elasticity (alpha), fit R² and trend, bounce and reversal checks.
An original hypothetical purchase task following the demand model of Koffarnus and colleagues. The price schedule and commodity units are our own. Unlike their 2015 analysis, this fit includes the free-price answer and uses a study-set k. Flat or all-zero curves retain observed indices and have no fitted elasticity. Nonsystematic-data checks flag answers for review and do not automatically exclude them. Compare adults using the same scenario and units.
Quality checks
Each session is marked valid, needs review or invalid, with the reason, before you see its scores.
Demand choices have no correct answer. Responses under 200 ms on at least half the price screens invalidate. Incomplete runs and the trend, bounce and reversal checks are flagged; zero demand is retained.
Why these rules
Stein et al. (2015) checks describe response patterns and do not automatically exclude a person's demand curve. A fit needs a complete ordered price series; missing answers are never zero purchases.
No percentile. Scores and quality flags only.
Running this test
Settings you can change
| Setting | Standard | Allowed |
|---|---|---|
| Commodity | Snack food (standard) | Snack food (standard), Alcohol, Cigarettes, E-cigarettes |
| Study currency | USD | USD, EUR, GBP, CAD, AUD, JPY, CNY, BRL, CHF, INR |
| Price multiplier | 1 | 0.1, 1, 10, 100 |
| Demand curve span (k) | 3 | 1 to 5 |
| Alcohol per standard drink (g) | 14 | 10, 12, 14 |
Yearly plans can change settings within these limits. Free and pay-as-you-go studies use the standard settings.
Need a setting this test does not have?
Devices and languages
- Untimed test: runs on desktops, laptops, tablets and phones. Participant devices
- Languages: English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese.
- Available on: Every plan, including the free plan.
- No percentile. Scores and quality flags only. How norms work
- Recruiting online? See the setup guides for Prolific, Sona Systems, CloudResearch Connect and Qualtrics.
Cite and describe
Participants completed the Purchase Task in a web browser (ConductCognition task version 1.0.0, scoring version 1.0.0; Koffarnus, Franck, Stein & Bickel, 2015; Stein et al., 2015), with the standard settings (commodity: Snack food; study currency: USD; price multiplier: 1; demand curve span (k): 3; alcohol per standard drink (g): 14). The main score was demand elasticity (alpha from the exponentiated demand curve, fitted in original quantity units including zeros).
ConductCognition versions: task version 1.0.0, scoring version 1.0.0. Every export records the versions each session used, for a methods section.
- Koffarnus, M. N., Franck, C. T., Stein, J. S., & Bickel, W. K. (2015). A modified exponential behavioral economic demand model to better describe consumption data. Experimental and Clinical Psychopharmacology, 23(6), 504-512. https://doi.org/10.1037/pha0000045
- Stein, J. S., Koffarnus, M. N., Snider, S. E., Quisenberry, A. J., & Bickel, W. K. (2015). Identification and management of nonsystematic purchase task data: Toward best practice. Experimental and Clinical Psychopharmacology, 23(5), 377-386. https://doi.org/10.1037/pha0000020
Source papers
Questions
How long does the Purchase Task take?
About 4 to 6 minutes, as listed in the test library.
What device does a participant need?
Untimed test: runs on desktops, laptops, tablets and phones. The browser must be Chrome, Edge, Firefox or Safari.
What scores does it produce?
Demand Elasticity, Demand Intensity, Breakpoint, Maximum Spending, Price at Maximum Spending, Fitted Intensity, Demand Fit R², Demand Fit Available, Demand Trend, Demand Bounce, Trend Flag, Bounce Flag, Reversal Flag, Zero Demand, Prices Answered, Comprehension Correct, Median Decision Time and Anticipations. Each session is also marked valid, needs review or invalid, with the reason.
How widely is the Purchase Task used in research?
178 papers from 2021 to 2025 name it in their title or abstract, up 1% compared with 2016 to 2020. That ranks it 166 of 582 test families in the ConductCognition test census (use grade C). Source: ConductCognition test census 0.39.0, counted 10 November 2026 from OpenAlex and ClinicalTrials.gov.
How much reliability evidence does the Purchase Task have?
In the published research, 7 papers report its test-retest reliability and 89 registered clinical studies use it as an outcome (evidence grade C in the ConductCognition test census).
Does it report a percentile?
No. Scores and quality flags only.
Which settings can a researcher change?
Commodity (Snack food (standard), Alcohol, Cigarettes, E-cigarettes), study currency (USD, EUR, GBP, CAD, AUD, JPY, CNY, BRL, CHF, INR), price multiplier (0.1, 1, 10, 100), demand curve span (k) (1 to 5) and alcohol per standard drink (g) (10, 12, 14). Settings can be changed on yearly plans; free and pay-as-you-go studies use the standard settings.
Which languages can participants use?
Participants can take this test in English, Spanish, French, German, Italian, Portuguese (Brazil), Chinese (Simplified) and Japanese, with its words in the same language. English is on every plan, and the other languages come with yearly plans. Have a native speaker read the machine-translated text before launch.
Is this a clinical test?
No. ConductCognition is for research use only. It runs, scores and exports the test; clinical interpretation is outside the platform.
Every test: the full test list.
Run this test in your next study
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