Being above the 200-day moving average is the simplest long-term trend filter. Its measured lift over baseline is the point.
The 200-day moving average is the most-watched long-term trend line. A stock trading above it is, by the simplest definition, in an uptrend; below it, a downtrend. Many long-only strategies simply refuse to hold names under their 200-day.
Above/below the 200-day doesn’t tell you to buy — it tells you which side of the trend you’re on. Used as a filter (only consider longs above it), it removes a large class of falling knives. The measured forward returns above vs below the line show how much that filter is worth.
Compare the above-200-day forward return to the all-bars baseline below. The gap — not the raw number — is the edge the trend filter actually adds.