Just want to start over, and here's my reasoning:
Before reading further, pls delve into the specifics of this article:
https://www.bridgewater.com/grappling-w ... everywhere
My thought:
Backtesting is a bit (not entirely) useless:
Why useless?
1) The impressive past performance of PP is based on four cornerstones - one of which is TLT.
TLT worked , because when the government faced economic headwinds or crisis, they can stimulate the economy by loose monetary policies. The logic behind: Interest rate down , TLT up, offsetting the downside risk of Equity.
2) However, todays enivronment is unprecedented.
Interest rate is close to negative territory.
There is not much room for the Fed to reduce the interest level.
So whether TLT can provide a upside as a great buffer to the whole portfolio seems a biggest uncertainty to PP followers.
3) This abnormality is not taken into account when we backtest

4) Some possible solution to the dire future of TLT:
GOLD and TIP, regarde by Ray Dalio, as a better alternative to TLT.
Phase Five (The Latest Version)
Ticker Name Allocation
Anti recession:
TLT iShares 20+ Year Treasury Bond ETF 7.50%
TIP iShares TIPS Bond ETF 7.50% ( Depression -> stimulative/reflationary policy -> involve high debt levels -> policy makers have an incentive to lower real debt burdens by lowering real yields -> often by generating inflation-> Falling real yields cause IL bonds to outperform )
GLD SPDR Gold Shares 25.00% ( Depression -> stimulative/reflationary policy -> fiat currencies are being debased -> favourable to GOLD)
Stock:
VTI Vanguard Total Stock Market ETF 25.00%
QQQ Invesco QQQ Trust 5.00%
Cash:
CASHX Cash 30.00%
Result:
Click here
Note the backtest totally ignore today's distorted interest rate and assume TLT would work fine forever.
There are some serious concerns about whether TLT work the charm like it does.
UPDATE 8 / AUG / 2020
Really thankful for all the comments and insights. Thought-provoking, and has got me thinking how to solve the puzzles
Came as a surprise the use of TIPs raises most concerns among the members, this is a concern. I decided to spend a morning to do some research on this issue.
Source of my findings (Its really worth reading, highly recommended):
https://personal.vanguard.com/pdf/ISGCTIPS.pdf
https://www.alliancebernstein.com/CmsOb ... ckbook.pdf
Insightful Summary:
1) When we view tools for inflation hedge, we must analyze it in two perspectives: inflation beta(sensitivity), and consistency of the inflation hedge.
2) When we talk about inflation, we must factor in two scenario: sudden unexpected inflation, or expected.
3) GOLD has a much stronger inflation beta to inflation, which the spike in gold price will act as a cushion to the inflation impact to the whole portfolio. But the problem of GOLD is it doesnt deliver consistent and reliable inflation hedge performance. This is because of a myraid of factors that can alter the value of GOLD , deviate its function as an inflation hedge
4) TIP has a moderate inflation beta, that means it is showing moderate negative correlation to inflation, this must disappoint PP investors who wants to see TIP can offset losses in other assets. However, its strengths lies in its much more reliable persistance in hedging inflation.
5) Short term TIP, no matter facing unexpected inflation or expected, are far more effective inflation-hedge tools than Long Term Duration TIP. This is seen in many researches tracing decades of historical data.
6) Other issues of TIP inclues deflation exposure, tax inefficiency, and possible manipulation by the producer of the inflation index.
7) Researches shows that in choosing your "shields" to defend the storm of inflation, the optimal approach is to go for diversification (Not only GLD and TIP but also other "real assets" such as real estates). This would help investors gain best long-term reward and risk ratio.
First amendment:
Lower the TIP allocation to 5% as a "diversifier" and give 20% to GOLD as "core"
Second amendment:
Add 5% to "TOK" as "diversifier" and lower the allocation for VTI to 20% as "core".
TOK increase exposure to a broad range of companies, ex Japan, in developed markets:
United States 71.30
United Kingdom 4.58
France 3.59
Canada 3.44
Switzerland 3.38
Germany 3.13
Australia 2.27
Netherlands 1.45
Hong Kong 1.08
Sweden 1.08
Third amendment:
Lower the CASH allocation to 20% as a "core" and give 5% to other currencies ETF as "core"
1% FXA - Aussie Dollar
1% FXB - British Pound
1% CYB - Chinese Yuen
1% FXY - Yen
1% FXF - Swiss
Phase Four (The Latest Version)
CASH 25%:
FXF Invesco CurrencyShares Swiss Franc 1.00%
FXY Invesco CurrencyShares Japanese Yen 1.00%
CYB WisdomTree Chinese Yuan Strategy ETF 1.00%
FXB Invesco CcyShrs British Pound Stlg 1.00%
FXA Invesco CcyShrs Australian Dllr Trust 1.00%
CASHX USD Cash 20.00%
GOLD + TIPS 25%:
GLD SPDR Gold Shares 20.00%
TIP iShares TIPS Bond ETF 5.00%
STOCK 25%
TOK iShares MSCI Kokusai ETF 5.00%
QQQ Invesco QQQ Trust 5.00%
SPY SPDR S&P 500 ETF Trust 15.00%
BOND 25%
TLT iShares 20+ Year Treasury Bond ETF 25.00%
Click Here - Result
CAGR are almost identical to Classic PP
Stdev Drops from 7.06% to 6.08%
Max. Drawdown Drops: 12.65 to 12.16%
Sharpe Ratio Increase: 0.9 to 0.93
Sortino Ratio Increase: 1.61 to 1.65
Why subtantial change to the allocation?
This is totally based on the assumption from the viewpoint of Ray Dalio
https://www.bridgewater.com/ray-dalio-m ... nvironment
1) Put it simply, Ray Dalio cautioned that the world is much more chaotic than before, and he suggests : "stock and currency in the portfolio" should be "as diverisified as possible, more than ever", and invest in "competitive countries".
2) Problem is, if u increase too much your stock exposure to the globe, u are potentially sacrificising the exceptional outperforming returns from US stock market, which has been last for more than 20 years, for lower geographical risk.
3) Whenever I attempt to increase international exposure, the annualized return shown in backtesting will deminished quickly. This is because of the fairly weak economic performance of other developed countries for almost two decades.
4) So the main questions is if the superpower status of US will be gone in future? and replaced by others? I don't know. But I can sense the fear of Ray Dalio. Which make me want to do sth about that.
5) 5% diversification is an attempt for balance between some diversification and higher return
Welcome for any comments and feedback

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UPDATE 6 / AUG / 2020
Studying different famous portfolio models, I believe there is always a way to optimize a "standard" portfolio to suit your risk and reward preference. So, the standard 25% rule is no exception.
GOAL:
Lower Maximum Drawdown (10% , is it possible to keep it at 10% while earning more?)
Higher Sharpe Ratio (at least higher than Classic PP)
Respectable return (at least 7%)
Lower Stdev (5 - 6%, I want a smoother equity curve)
Sortino Ratio (Lower Downside Risk)
THis is the standard PP performance:
Click here
PP does a fanastic job in outperforming the standard 70:30 stock bond allocation in the sense of MUCH lower Stdev + Max. Drawdown and far superior Sharpe Ratio + Sortino Ratio.
Inspired by Ray Dalio AW, I think the standard PP can use TIPs as another tool to manage the inflation risk.
AW strategy has considerable emphasis on the use of TIPs, the value of TIPs is non-negligible.
If it is inferior to GOLD, Why they dont fully use GOLD?
Devling into the specifics, I start finding TIPs has its own merits/drawbacks vs GOLD
Click here
1) TIPs are much less volatile and risky:
- Max. Drawdown: 11.79% vs -42.91% !!
- Stdev: 5.58% vs 17.42% !!
Some reasons I guess: because 1) its an asset backed by US government, 2) its return rate is contractually linked to inflation rate with more certainty than GOLD
2) TIPs a huge annual correlation with GOLD. This somehow proves its value in substituting GOLD for inflation protection
3) Due to its lower volatility, TIPs also has lower CAGR
- CAGR: 4.08% vs 9.70%

To put it simply:
Gold volatility is quite crazy, while Tips can act as a stability cushion.
Gold annualized return is impressive. (From 2005)
What is the opportunity we see from the two extreme difference in these two assets:
Instead of solely relying on GOLD, we attempt to add TIPs in the portfolio.
This will help the portfolio capture the benefit of two inflation-proof assets.
To maintain impartial view between two assets,
equal allocation will be given to TIPs and GOLD
12.5% TIPs
12.5% GOLD
Let's see would the performance of TIPs hugely affected by the "sluggish" return of TIPs?
Click here
Stdev and Max Drawdown have both seen much better outcomes.
Stdev: 5.57% vs 6.71%
Max Drawdown: 12.63% vs 10.56%
Which is quite compelling
Of course, without the fuel of GOLD, annualized return would drop
7.73% -> 6.94%
Sharpe Ratio increased from 0.96 to 1
===============
So this is the Phase one of the modification
GLD SPDR Gold Shares 12.50%
TIP iShares TIPS Bond ETF 12.50%
CASHX Cash 25.00%
TLT iShares 20+ Year Treasury Bond ETF 25.00%
SPY SPDR S&P 500 ETF Trust 25.00%
===============
Phase two:
There must be something that can be used as fuel
Here we attempt to raise our stake in US tech by as little as 5%
GLD SPDR Gold Shares 12.50%
TIP iShares TIPS Bond ETF 12.50%
CASHX Cash 25.00%
TLT iShares 20+ Year Treasury Bond ETF 25.00%
SPY SPDR S&P 500 ETF Trust 20.00%
QQQ 5.00%
5% has its reasons, we cant add too much weighting to US tech, otherwise it can be risky.
In case of US tech bubble (which I find it unlikely, because the bubble in 2000 stemmed from the inability of US tech to materialized their fantasy and big plan to solid earnings, which is different from this era),
significant loss to QQQ will be manageable to the whole account
Here is the astonishing result:
Click here
Phase 2 inherit the stability from phase 1:
-10.37% Max Drawdown in 2008
-5.60% Stdev
But the 5% QQQ does improve the return
-7.23% CAGR (HEY! with much lower risk, the return is only 0.09% behind 70 stock : 30 bond strategy, and 0.5% behind classic PP!

In terms of RISK / REWARD relationship
- 1.05 Sharpe ratio
- 1.82 Sortino Ratio , far higher than Phase 1 and classic PP
====================
Any suggestions or comments!?