If you're puzzled why large injections into the money supply have failed to send gold prices higher, you're not alone. The answer is not so simple, since many factors can have an impact on the price of gold. For now we will forget about politics and gold as a fear trade, focusing solely on the monetary, inflationary, and economic aspects.

Over the last six months the SPDR Gold Trust ETF (NYSEMKT:GLD), the largest physically backed gold ETF, looks to be stuck. Since movements in silver prices strongly correspond to gold, the iShares Silver Trust ETF (NYSEMKT:SLV) has also found itself in a lull.

When looking at historic catalysts for gold and silver rallies it should comes as no surprise that these precious metals are range-bound. Here we'll examine those factors at work, one at a time, with the hope of helping you better understand and time your investments in the SPDR Gold Trust ETF and the iShares Silver Trust ETF.

In a recent article, I discussed how monetary effects were found to have two distinct components: money supply and velocity, which is how fast a dollar is turned over in a given period. The conclusion was that since the onset of the Great Recession in 2007, the velocity of money in the United States has fallen sharply, at an annual average rate of 3.1%. This decline has offset average annual excess money growth of 4.9%, resulting in an average annual increase in the GDP deflator of 1.8%. Future increases in velocity would be a likely contributor to increases in inflation and therefore gold prices. Watching for increases in this key metric could provide some insight as to when gold could see higher prices.

Energy prices
The oil crisis in the 1970s comes to mind right away. High energy prices contributed to inflation that led to some of the highest interest rates in a generation to control the outbreak. Remember, inflation has a direct effect on gold and silver pricing. If high rates of inflation threaten to to render paper currency less valuable, people often turn to hard currency like gold or silver as a store of wealth. Given the finite nature of these commodities, prices naturally spike as a result of this increased demand. But with oil prices in their tightest range in five years, this seems to be under control -- for now.

Low interest rates
Prolonged low interest rates can often be a source. As rates are reduced firms and households often take advantage of the decreased cost in borrowing to invest or spend. This short-term demand increase for goods and services tends to push wages and other costs higher, which can lead to commodity and wage based inflation, discussed below. But with the Fed under a historically unparalleled level of scrutiny by a variety of players regarding our current low interest rates, this issue appears to be monitored sufficiently.

Wage inflation
Economists may debate the finer points of this issue but the negative relationship between unemployment and inflation is widely held. As unemployment decreases competition for workers increases, driving up their wages. Though unemployment has been falling, Fed Chair Janet Yellen recently indicated that it is premature to begin drawing conclusions about when wage inflation will manifest. Recent data from the commerce department regarding lackluster wage growth seem to support Yellen's trepidation on this issue. Her statements regarding the labor market and wage competition should be monitored for indicators of potential wage inflation.

Other factors
Trade deficits are often cited as potential contributors to a weakening currency by economists. But it appears that the magnitude of the deficit and the stability of the country running the deficit must be considered. The Federal Reserve Bank of San Francisco found that in the short run, the relationship between the trade deficit and the dollar is weak, and the value of the dollar is determined largely by investor preferences for U.S. dollar assets. The desire for U.S. debt by foreigners means this issue seems to be under control.

Economic uncertainty often plays a role. If a country is in turmoil their currency may be called into question, sending people scrambling to hold hard currencies as a store of wealth. But with the United States being seen as the most stable economy, albeit in a tepid global environment, and the favored reserve currency for approximately 85% of central banks globally, that worry isn't on the table anytime soon.

Finally, supply issues can play a key role. Given a potentially endless demand for this finite metal but the increasing difficulty in finding it, prices will inevitably increase. If prices increase as a result of supply/demand imbalances, this could ultimately benefit the gold miners best represented as a whole by the Market Vectors Gold Miners ETF (NYSEMKT:GDX).

But as noted earlier, prices remain in a lull, suggesting tepid demand. When poor macroeconomic conditions hit, sometimes the businesses operating in that sector can fare even worse. As price declines hit a commodity, those same numeric declines often hit the profit margins, translating into even larger percentage decreases in terms of earnings. This would explain why recent price declines in the Market Vectors Gold Miners ETF are significantly larger than those of the SPDR Gold Trust ETF  or the iShares Silver Trust ETF. But when gold regains favor that logic also works on the way up, meaning the Market Vectors Gold Miners ETF could see the largest gains during bullish times.

The payoff
There are a variety of factors that affect gold and silver pricing. Understanding these factors individually will help compose the big picture for precious metals. Here we just touched on a few such as monetary influences, historic inflationary causes, and supply issues. Currently we noted that the factors increasing precious metals prices seem to be under control, but it won't be like that forever. Staying on top of developments in these key areas will help investors more accurately predict the future of the Market Vectors Gold Miners ETF, the SPDR Gold Trust ETF, and the iShares Silver Trust ETF.

James Catlin has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.