Stock Market Participation and Aktiesparkonto Experiment

Last registered on May 11, 2026

Pre-Trial

Trial Information

General Information

Title
Stock Market Participation and Aktiesparkonto Experiment
RCT ID
AEARCTR-0018546
Initial registration date
May 04, 2026

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
May 11, 2026, 8:01 AM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Locations

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Primary Investigator

Affiliation
University of Copenhagen

Other Primary Investigator(s)

PI Affiliation
University of Copenhagen

Additional Trial Information

Status
In development
Start date
2026-05-05
End date
2028-06-01
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
Stock market participation remains low across the world despite favorable conditions. Recent evidence (Duraj et al., 2025) suggests a key barrier is the misperception that successful investing requires expertise, continuous monitoring, and active trading. A related policy puzzle is the limited uptake of the Aktiesparekonto (ASK), a tax-advantaged stock savings account that is planned to be introduced across the EU. At the other end of the financial spectrum, financially constrained households tend to underestimate spending on recurring subscriptions.
This pre-registered survey experiment, fielded on a representative sample of the Danish adult population (N=70,000), screens respondents on financial constraint and investment status and routes them into one of three survey and experimental arms.
Unconstrained non-investors are randomized to a video explaining the efficient market hypothesis, diversification, and index funds, or to a control video on the stock market generally. Unconstrained investors without an ASK are randomized to information about the account's features and tax advantages, or to a passive control. Constrained respondents — those unable to cover a 10,000 DKK unexpected expense without borrowing — are randomized to listing their subscriptions in detail, or to a general subscription question to prompt them to consider automatic expenses.
We measure four classes of outcomes: immediate beliefs, stated intentions, self-reported behavior in a November 2026 follow-up survey, and actual stock market entry and ASK take-up observed in Danish administrative registry data. The design traces the pipeline from beliefs to intentions to behavior across three financial-decision contexts and uses administrative data to mitigate self-report bias and intention–behavior gaps that limit much of the existing literature on household financial behavior.
External Link(s)

Registration Citation

Citation
Gravert, Christina and John Kramer. 2026. "Stock Market Participation and Aktiesparkonto Experiment." AEA RCT Registry. May 11. https://doi.org/10.1257/rct.18546-1.0
Experimental Details

Interventions

Intervention(s)
Experiment 1: The treatment video briefly explains the efficient market hypothesis (EMH), diversification and index funds; the control video explains the stock market generally.
Experiment 2: The treatment group is shown facts about the ASK, including, but not limited to the fact that it is tax-advantaged in certain situations. The control group is passive.
Experiment 3: The treatment group is prompted to think about their subscriptions in categories, the control group is only asked to estimate the total.
Intervention Start Date
2026-05-05
Intervention End Date
2026-12-01

Primary Outcomes

Primary Outcomes (end points)
Experiment 1. Opening a trading account in 2026 - measured in the register data
Experiment 2. Opening a tax-advantaged account (ASK) in 2026 - measured in the register data
Experiment 3: Intending to cancel at least one subscription - measured in the survey
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Self-reported measures of the primary outcomes in a follow-up survey in November 2026
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
To address our research questions, we conduct an online survey with a representative sample of the Danish population aged between 18 and 55. We invite 70,000 randomly sampled individuals between 18 and 55 to participate through the Danish digital mailbox. The survey will be sent out on the 5th of May 2026 at 9am CET and will close on the 24th of May 2026 at midnight. We will send a reminder on the 19th of May. In November 2026, we will send a follow up survey to a subset of all participants who completed the survey.

The survey experiment has three arms based on respondents financial liquidity and their current investment status.
Arm 1: Respondents who could afford an unexpected expense of 10,000DKK and who are NOT currently investing in the stock market
Arm 2: Respondents who could afford an unexpected expense of 10,000DKK and who are currently investing in the stock market
Arm 3: Respondents who could NOT afford an unexpected expense of 10,000DKK

All participants start the same survey and are asked some general questions about their finances and financial literacy, but are then funneled into their respective arms based on their answers.

Participants in arm 1 are then randomized into a treatment or control video about stock market investing. The treatment video briefly explains the efficient market hypothesis (EMH), diversification and index funds; the control video explains the stock market generally.
Participants in arm 2 are randomized into a treatment and control group. The treatment group is shown facts about the ASK, including, but not limited to the fact that it is tax-advantaged in certain situations. The control group receives no information.
Participants in arm 3 are randomized into two groups. The treatment group is prompted to think about their subscriptions in categories, the control group is only asked to estimate the total.

We then elicit some personality traits for all respondents.
Experimental Design Details
Not available
Randomization Method
Question Pro randomizes participants who reach the randomization stage of the survey.
Randomization Unit
Individual respondents are randomized.
We also randomize incentives to participate to the survey (3 groups).
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
No clusters
Sample size: planned number of observations
We invite 70,000 participants to the survey and expect a 10% response rate, resulting in 7000 responses.
Sample size (or number of clusters) by treatment arms
According to aggregate statistics, ca 20% of Danes cannot cover a 10,000 DKK unexpected expense without borrowing. That means 1400 respondents will be funneled into the constrained survey. Ca. 25% of all Danes invest in the stock market, that is 1750 respondents, as we believe there is little overlap between the ones who already invest and the most economic vulnerable. Around 30% of investors already have an ASK, which leaves us with 1225 respondents for the ASK experiment. That leaves 3850 expected responses for the survey of non investors. The baseline 12-month account-opening rate among non-investors is 3%.
We randomize participants 50/50 into treatment and control for each arm.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
Non-investors: Under these assumptions, we are powered (beta = 0.80, alpha = 0.05) to detect a minimum treatment effect of approximately 1.5 percentage points on the non-investor account-opening outcome (outcome is opening any trading account). Investors: We are powered to detect a 3.5 pp increase in ASK opening among the investors, at an estimated baseline of 3.5% (outcome is opening an ASK). Constrained: We assume that 30% of individuals in the control group will want to cancel a subscription they have after treatment. We are powered to detect a 8pp increase in intentions to cancel a subscription (outcome is intention to cancel a subscription).
IRB

Institutional Review Boards (IRBs)

IRB Name
University of Copenhagen, Department of Economics
IRB Approval Date
2025-12-18
IRB Approval Number
N/A
Analysis Plan

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