Comparing Berkshire Hathaway's portfolio to Vanguard's is like comparing a restaurant's menu to a grocery store's inventory. They serve completely different purposes.
Yet this is exactly what most people do with 13F data — compare managers without considering that they have fundamentally different mandates, strategies, and constraints.
Filer groups fix this problem.
What filer groups are
A filer group is a curated set of 13F filers that share similar characteristics — strategy type, AUM range, investment style, or institutional category.
Instead of comparing all 6,000 filers against each other, you compare within groups where the comparison is meaningful.
Why random comparisons fail
| Comparison | Why it's misleading |
|---|---|
| Berkshire vs. Vanguard | Concentrated active value vs. passive index — completely different objectives |
| ARK vs. Bridgewater | Thematic growth vs. macro all-weather — different universes |
| Jane Street vs. Dodge & Cox | Market maker vs. value investor — one is hedging, the other is investing |
| A $500M RIA vs. Fidelity ($2T) | Size constraints make their portfolios incomparable |
Useful filer group categories
By strategy type
Value investors: Berkshire, Dodge & Cox, Tweedy Browne, Baupost
- Compare: concentration, sector tilts, turnover, conviction sizing
- Signal: when multiple value managers buy the same name, it's a deep value consensus
Growth managers: Jennison, ARK, Baillie Gifford, Tiger Global
- Compare: tech concentration, position turnover, drawdown behavior
- Signal: when growth managers start trimming the same name, momentum may be fading
Quant/systematic: Renaissance, D.E. Shaw, Two Sigma, Citadel
- Compare: position count, concentration, factor exposure
- Note: 13F is least useful here — quant strategies are multi-legged and the 13F shows one leg
Activists: Elliott, Pershing Square, Third Point, Starboard
- Compare: number of activist positions, holding period, resolution outcomes
- Signal: when multiple activists converge on the same stock, expect fireworks
By AUM range
Mega ($100B+): Vanguard, BlackRock, Fidelity, State Street
- Comparison within this group shows: flow trends, passive vs. active split, market structure
Large ($10-100B): Wellington, MFS, Jennison, American Century
- Comparison shows: active conviction differences, sector preferences, style drift
Mid ($1-10B): Concentrated hedge funds, boutique managers
- Comparison shows: highest-signal stock picks, contrarian bets, emerging themes
Small (<$1B): Family offices, small RIAs, startup funds
- Comparison shows: niche ideas, small-cap picks (but noisy and less reliable)
By institutional type
Market makers: Jane Street, Susquehanna, Optiver, Citadel Securities
- Their 13Fs reflect inventory and hedging, not investment views
- Compare within this group to understand market structure, not to find stock picks
Bank trading desks: Goldman, Morgan Stanley, BNP Paribas
- Similar to market makers — hedging and client facilitation
Pension funds / endowments: CalPERS, Harvard Management, Yale
- Long time horizons, specific mandates, governance constraints
Wealth managers / RIAs: Focus Financial, Hightower, various RIAs
- ETF-heavy, model portfolio-driven, low individual stock signal
How to build and use filer groups
Step 1: Define your question
What are you trying to learn?
- "What are value investors buying?" → Value investor group
- "Where is smart money concentrating?" → High-conviction active group
- "What's the passive baseline?" → Mega passive group
Step 2: Select 5-8 comparable filers
Keep groups small enough to analyze thoroughly. 5-8 filers per group is ideal.
Step 3: Compare the same metrics across the group
- Top 10 overlap (how similar are they?)
- Shared new positions (consensus entries)
- Shared exits (consensus exits)
- Concentration differences (who's most/least convicted?)
Step 4: Look for deviations within the group
The most interesting signal is when one member of a peer group does something different from the rest. A value investor buying a growth stock. A passive-heavy manager adding an unusual active position. A market maker showing a directional tilt.
Deviations within a well-defined peer group are the highest-signal data points in 13F analysis.
Originally published at 13F Insight
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