Sarah Mitchell
Education Editor
Investment Education Editor at 13F Insight. Breaks down complex institutional data into actionable insights for individual investors.
A note from Sarah
Hi, I'm Sarah. I spent four years at Vanguard's Investor Education team, where my whole job was making 401(k) statements feel less like tax forms and more like something a person could actually understand.
I'm here at 13F Insight to do the same thing for institutional data. If you've ever read a headline like "Berkshire Bought Apple" and thought "okay but what does that actually mean for me," that's the gap I want to close.
I'll never assume you know what a CUSIP is. I'll always tell you why a number matters before I give you the number. And if a guide of mine ever leaves you more confused than you started, that's on me — let me know and I'll rewrite it.
Articles by Sarah Mitchell (822)
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10b5-1 Plan Sales vs Discretionary: How to Read Form 4
Half of all 'CEO dumps stock' headlines are mechanical 10b5-1 plan executions, not discretionary conviction signals. A practical guide to spotting plan-driven sales in the Form 4 record and finding where real insider signal lives.
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13F 'NEW Position' Labels: 3 Causes, Only One Is a Real Buy
The 'NEW position' label on 13F filings has three different underlying causes — only one of which is a genuine new buy. Misreading the label overstates a fund's directional activity. Decision tree + structural artifact examples.
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Director Form 4 Sales vs CEO Form 4 Sales: Reading the Difference
A long-tenured director selling $71M of stock and a CEO selling $71M of stock are not the same signal. Here is how to read each Form 4 with the correct interpretive frame.
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Founder-Controlled Cap Tables: Reading 13D/A Family Block Filings
When a founder family files a Schedule 13D/A reflecting a major share movement, the percent-of-class line tells one story and the underlying transactions tell another. Here is how to read both without confusing structure for sentiment.
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13F Share Count vs Weight: Two Columns, Two Stories
A 13F position can hold a steady weight while the share count drops by a third — and vice versa. Here is how to read both columns together so the trade isn't hidden by the price-driven noise.
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How to Spot a 10b5-1 Plan in Form 4: The VWAP Fill Profile
Most 'CEO sells stock' headlines misread the underlying Form 4 cadence. Pre-scheduled Rule 10b5-1 plans and discretionary block sales execute very differently, and the data tells you which is which — if you know what to look for in the fill profile, daily share count, and continuation pattern.
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When 13F Reported Value Lies: The BRK/A and 5 Other Traps
13F filings report dollar value across millions of institutional positions, but the headline number can wildly mismatch economic ownership. Six common traps — Berkshire Class A's per-share price distortion, options notional reporting, market-maker inventory, and others — that every reader should learn to spot before drawing portfolio inferences.
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Mechanical vs View-Driven Holders: Reading 13F Beyond Top Five
BlackRock, Vanguard, and State Street appear at the top of nearly every large-cap institutional holder list. Reading their presence as 'smart money endorsement' is a category error. This guide covers how to distinguish mechanical index-driven ownership from view-driven active conviction.
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When 13F Position Counts Swing: Portfolio Rebuild vs Rotation
Hedge fund 13F position counts often swing dramatically across quarters, and the dollar AUM swing usually distracts retail readers from the more useful signal — what the changing position count says about manager intent. This guide breaks down the diagnostic patterns with current examples.
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How to Spot a Rule 10b5-1 Plan Sale in Form 4 Filings
Insider sales filed on Form 4 often look identical at the dollar-headline level but split cleanly between plan-driven and discretionary at the mechanics level. This guide covers the structural signatures retail investors can use to tell them apart.
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Post-Merger Founder Form 4s: Why Acquirer Selling Isn't Bearish
After a stock-funded merger closes, founders of the acquired company suddenly appear as Form 4 sellers of the acquirer's stock. Here's how to read that cycle without misinterpreting it as a bearish signal.
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Reading a PE-Firm 13F: When 99% in One Stock Means Distribution
PE-firm 13Fs look bizarre on first read — sometimes 95% or more of disclosed value sits in a single stock. The explanation is structural: you're looking at post-IPO retained equity, not a portfolio.
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Capital Group's Three 13F Filers: Reading CWI, CRGI, and CII
Capital Group — one of the world's largest active asset managers — files three separate 13Fs through sister entities: Capital World Investors, Capital Research Global Investors, and Capital International Investors. Knowing which is which is essential for reading the active money on any US stock.
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SEC Accession Numbers: What That 18-Digit Code Actually Means
Every SEC filing on EDGAR has an accession number — an 18-digit code like 0001067983-25-000123. The three segments encode the filer's CIK, the year, and the sequence number. Understanding the structure makes the SEC record navigable.
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The 2026 Vanguard 13G Reshuffle: Reading 0% Exits
Across GM, AMZN, GOOG, Roku, and dozens of other large-caps, Vanguard Group Inc. filed Schedule 13G/A exits at 0.00% in March 2026 — and Vanguard Capital Management LLC filed new 13Gs at similar percentages weeks later. This is a reporting-entity reshuffle, not a real position exit.
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The 13F 45-Day Window: Why Q1 Filings Land May 15
The SEC 13F filing window is 45 days after quarter end. Q1 2026 closes March 31, so the deadline is May 15, 2026. This guide explains the window, who files when, and how to read the early-vs-late filer pattern.
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10b5-1 Plan Footnotes on Form 4: Reading Guide
What the Rule 10b5-1 plan footnote on a Form 4 actually contains, the four checks to run on every plan-footnoted sale, and the safe editorial framing when the footnote is missing.
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Foreign-Domiciled Passive Sleeves: Reading Their 13Fs
How to identify a foreign-domiciled passive sleeve from a 13F holdings table — three structural tells, why the misread matters, and a worked example from a UK Vanguard filer.
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13D vs 13G Filings: What Active vs Passive Intent Really Means
Both Schedule 13D and 13G disclose 5%+ ownership, but they signal opposite things about what the filer intends to do. Three current examples — Sanders Capital, Micron, and the Stryker family — show why the distinction is doing real interpretive work.
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Form 4 Transaction Codes: How to Read S, G, M, F, and 10b5-1
How to read a Form 4 transaction code without falling into the most common SEC EDGAR trap — distinguishing open-market sales from gifts, plan-driven executions from discretionary trades, and Table I from Table II ownership.