Recommended Free Tools
iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
The preregistered SPY turn-of-month test found a positive return difference, but it did not meet the decision rule set before analysis. Its confidence interval included zero, its calendar-rotation test returned p = 0.212, and its net results fell short of the required matched-exposure benchmark. That is an inconclusive result for this test—not proof that the effect never existed or has disappeared.
What the test set out to measure
The turn-of-month effect is the historical claim that stock returns cluster around the transition between calendar months. This test used SPY daily returns from January 29, 1993, through September 24, 2026, covering 8,470 reported return bars. Its window was the final trading day of each month plus the first three trading days of the next month: four consecutive trading days, or 19.1% of the reported sample.
The author says the hypothesis and decision rules were frozen before examining the results. The preregistration file was identified by SHA-256 hash 04396d92f6a45d2ffebff0faff7c4e31cfde983e11d3bdfd5b5bc9f8e7d8cba2. The methods, figures, and hash are reported by the author; the underlying file and calculations have not been independently reproduced here. Read the author’s account of the SPY test.
Why a positive estimate still failed
The average return in the selected window was higher than on other days, but the preregistered rule required all five of its decision clauses to pass. They did not. A positive point estimate is not, by itself, evidence that the effect is distinguishable from noise or clears a prespecified practical benchmark.
#1 Best Overall
- Read Before You Buy — No Video Output: These adapters support charging and USB 2.0 data transfer, but cannot transmit video signals. Except for standard USB webcams (which use USB data only), they are not compatible with HDMI/DisplayPort cables, video-capable USB-C hubs, or docking stations with video output.
- Convert USB-A Ports to USB-C: Designed to connect USB-C earphones, cables, flash drives, card readers, and other USB-C accessories to standard USB-A ports. Plug-and-play with no drivers or software required.
- Aluminum Alloy Housing: Built with a sturdy aluminum alloy shell that aids in heat dissipation and protects against daily wear and scratches. Designed to maintain a stable and secure connection.
- Compact & Travel-Friendly: The ultra-compact design allows the adapter to stay plugged into your device without blocking adjacent ports or adding bulk, reducing wear and tear on your original USB ports.
- 12-Month Warranty: Backed by a 12-month manufacturer warranty for peace of mind. Designed to meet strict quality control standards for reliable everyday performance.
| Reported result | What it means for the decision |
|---|---|
| In-window mean: +7.28 basis points per day; other-day mean: +3.33 bps/day; difference: +3.95 bps/day | The estimated difference was positive. |
| Stationary-bootstrap 95% confidence interval for the difference: −2.02 to +9.80 bps/day | The interval included zero, so the estimate did not establish a positive difference under this analysis. |
| Circular-rotation null test: p = 0.212 | The result did not meet the test’s significance cutoff. |
| At 2 bps round-trip cost: annualized return 3.25%; matched-exposure null’s 95th percentile 3.38%; observed rule at the 93.8th percentile | It fell short of the preregistered 95th-percentile hurdle. |
| At 5 bps round-trip cost: annualized return 2.88%; matched-exposure null’s 95th percentile 3.02%; observed rule at the 93.7th percentile | It also fell short at this cost assumption. |
The cost comparisons use the author’s reported annualized figures and tested cost assumptions; they are not independently reproduced. The benchmark matters: the author compared the four-bar rule with randomly positioned four-contiguous-bar windows within each month, matching exposure rather than comparing a partly invested strategy only with cash.
How the preregistered checks were designed
Calendar alignment and uncertainty
The author reports using a circular-rotation null to test whether returns aligned unusually well with the calendar labels while preserving the return series and the number and spacing of labeled days. The confidence interval came from a stationary bootstrap with a mean block length of 20 trading days and 10,000 resamples. These choices were specified in the preregistration, according to the author.
Rank #2
- 5-in-1 USB-C Hub: Experience comprehensive connectivity featuring a Power Delivery input, two USB-A 2.0 ports, a USB-A 3.0 port, and an HDMI port. (Note: The USB-C power delivery input port is only for connecting an external wall charger to power your laptop and cannot power peripheral devices.)
- 90W Pass-Through Charging: Achieve optimal charging with 90W pass-through power to your laptop, supported by a total input of 100W, with the hub reserving 10W for operational efficiency. (Note: Wall charger not included.)
- Quick Data Transfers: Accelerate your productivity with rapid data transfers using a high-speed 5Gbps USB 3.0 port and two 480Mbps USB 2.0 ports.
- 4K HDMI Display: Enhance your visual experience with a hub capable of delivering 4K resolution at 30Hz in both mirror and extend modes. Please note that this hub is compatible with MacBook (macOS 12 and newer), Windows 10 and 11, ChromeOS, and laptops equipped with DP Alt Mode and Power Delivery. Note: This device is not compatible with Linux.
- What You Get: Anker USB-C Hub (5-in-1, 4K HDMI), welcome guide, 18-month warranty, and our friendly customer service.
Costs and execution timing
Costs were treated as part of the decision, not as an afterthought. The reported net-return comparisons at 2 and 5 bps round-trip costs both missed the required percentile threshold. Separately, the author reports that delaying execution by one bar reduced gross return from 3.50% to 3.01%. This illustrates why an apparent calendar pattern can depend on implementation assumptions as well as on the return estimate.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Split-sample consistency
The estimated difference had the same sign in both reported halves: +5.84 bps/day in 1993–2009 and +2.03 bps/day in 2010–2026. Neither half was individually significant, and the late-half interval included zero, so the split-sample clause failed. Matching signs are not enough to establish a persistent effect when the intervals remain uncertain.
Rank #3
- Sleek 7-in-1 USB-C Hub: Features an HDMI port, two USB-A 3.0 ports, and a USB-C data port, each providing 5Gbps transfer speeds. It also includes a USB-C PD input port for charging up to 100W and dual SD and TF card slots, all in a compact design.
- Flawless 4K@60Hz Video with HDMI: Delivers exceptional clarity and smoothness with its 4K@60Hz HDMI port, making it ideal for high-definition presentations and entertainment. (Note: Only the HDMI port supports video projection; the USB-C port is for data transfer only.)
- Double Up on Efficiency: The two USB-A 3.0 ports and a USB-C port support a fast 5Gbps data rate, significantly boosting your transfer speeds and improving productivity.
- Fast and Reliable 85W Charging: Offers high-capacity, speedy charging for laptops up to 85W, so you spend less time tethered to an outlet and more time being productive.
- What You Get: Anker USB-C Hub (7-in-1), welcome guide, 18-month warranty, and our friendly customer service.
What the stronger alternative window does—and does not—show
The author reports one alternative window with a larger estimated difference, +8.35 bps/day, and p = 0.020. It did not meet the stated Holm-corrected threshold of 0.0167 for three alternatives. The author also notes that the plausible search space was larger than those three windows, so correcting only across the registered subset would understate the selection problem. Treat this result as a follow-up hypothesis, not as a successful discovery.
How this compares with historical claims
Robert A. Ariel’s 1987 paper, “A monthly effect in stock returns,” reported that mean returns in its sample were positive immediately before and during the first half of calendar months, and indistinguishable from zero in the second half. That historical result used a different operational definition from this SPY test; it is context for the broader claim, not a direct replication. Ariel’s paper in the Journal of Financial Economics.
Rank #4
- Dual Converters, Infinite Potential：Includes 2× USB C male to USB A female adapters and 2× USB A male to USB C female adapters. Perfect for a wide range of uses—tablets with Bluetooth keyboards, expand USB ports on macbook, and more. Two different converters for all your daily needs
- Next-Level 10Gbps & 3A Charging: No more slow 480Mbps, this usb to usb c adapter has a transfer speed of up to 10Gbps, allowing you to do more transferring in less time. This usb adapter fits both USB A and USB C charger, supporting up to 3A fast charging
- Upgraded Exquisite Craftsmanship: With an aluminum alloy housing and metal connector, the usbc to usb adapter is extremely durable and sturdy. Rigorously tested to withstand more than 10,000 times of plugging and unplugging, ensuring long-lasting performance
- Broad Compatible: The usb c to usb adapter widely supports all USB C/ USB A devices like laptops, tablets, cellphones, car chargers, and phone chargers. Such as compatible with MacBook Pro/Air 2023/2022, Thunderbolt 4/3 Devices,Apple MagSafe Watch 9/8/7/SE/Ultra, iPad Pro 2022/2021, Samsung Galaxy S23/S20/S10, and iPhone 17/16/15 Pro. Plug and play
- Please Note: To reach 10Gbps speed, keep the cable under 3.3 ft. For USB A Male to USB C adapters, try flipping the USB C connector. USB C Male to USB A adapters support bidirectional 10Gbps transfer within 3.3 ft
A J.P. Morgan analysis reproduced in an SEC-hosted filing reported historical annualized S&P 500 returns through October 2022 of 26.06% for the first four trading days of the month, 1.53% for middle days, and 18.72% for the last two trading days. The corresponding share of positive-return days was 56%, 52%, and 54%. Those are historical group statistics, not a forecast or proof that a strategy could capture an edge after costs. The filing discusses possible explanations such as portfolio adjustments, pension reinvestment, and systematic retail mutual-fund investments, while cautioning that other factors may be responsible and future persistence is not assured. SEC-hosted filing containing the historical statistics and discussion. For broader academic context, see the AEA overview by Richard H. Thaler.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsWhat this failure can establish
- For the specified SPY window, sample, statistics, and decision rule, the reported result did not clear the preregistered bar.
- The point estimate was positive, but its uncertainty interval and rotation test did not establish a reliable calendar-linked difference under the reported methods.
- The tested cost cases were near the matched-exposure threshold but remained below it.
What it cannot establish
- It does not prove that the turn-of-month effect never existed or is now absent. The author says the sample was too short to distinguish an effect of the estimated size from zero, estimating roughly 2.2 times the sample—about 75 years—would be needed at the stated volatility. That power estimate is the author’s, not an independent evaluation.
- It does not establish whether the pattern appears in other indices, countries, or asset classes. The analysis covers SPY only and includes no cross-instrument replication.
- It does not show that a historical calendar pattern will persist or can be traded profitably. Adjusted historical data can also be revised retroactively; the author says the conclusion is pinned to a hashed data snapshot.
Transparency details and limits
The author discloses that the first run calculated from an in-memory data pull while saving a snapshot rounded to six decimal places. The author says the I/O behavior was fixed and the same snapshot rerun, with the verdict and all five clause outcomes unchanged. This is an author disclosure, not an external audit of the data or code.
Best Value
- 5-in-1 Connectivity: Equipped with a 4K HDMI port, a 5 Gbps USB-C data port, two 5 Gbps USB-A ports, and a USB C 100W PD-IN port. Note: The USB C 100W PD-IN port supports only charging and does not support data transfer devices such as headphones or speakers.
- Powerful Pass-Through Charging: Supports up to 85W pass-through charging so you can power up your laptop while you use the hub. Note: Pass-through charging requires a charger (not included). Note: To achieve full power for iPad, we recommend using a 45W wall charger.
- Transfer Files in Seconds: Move files to and from your laptop at speeds of up to 5 Gbps via the USB-C and USB-A data ports. Note: The USB C 5Gbps Data port does not support video output.
- HD Display: Connect to the HDMI port to stream or mirror content to an external monitor in resolutions of up to 4K@30Hz. Note: The USB-C ports do not support video output.
- What You Get: Anker 332 USB-C Hub (5-in-1), welcome guide, our worry-free 18-month warranty, and friendly customer service.
The practical value here is the audit trail: a stated hypothesis, a fixed decision bar, an exposure-matched null, explicit costs, and a near-miss recorded as a miss. That makes the conclusion interpretable without turning a positive estimate into a claim of discovery.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
