When a Folio doesn’t have any transaction data (e.g. it’s just a watch list) we still publish performance charts. This is a simulated performance generated from the 1 year price histories of all the securities in the Folio. It is calculated as follows:
We create an equal weighted portfolio of all the shares in the list using the share price from a year ago which creates the base valuation.
We move forwards daily in time from the date a year ago. On each date the portfolio is revalued according to the new share prices.
The year’s daily valuation data is published as a performance chart.
This is a very useful feature for seeing how a list of shares performed historically. It is a capital return only performance history, we do not include dividends in the calculation.
Regarding what can be inferred from the chart - that depends on how it is being used. If the list of stocks has come from the screener then it doesn't mean that that's how the screen would have performed historically. In other words, it is not a backtester.