Shares in online estate agency Purplebricks (LSE: PURP) have soared by around 7% today despite no news flow having been released by the company. This is somewhat surprising since it was announced today that the Royal Institute of Chartered Surveyors (RICS) expects house prices to fall in the next few months as fears surrounding the EU referendum and changes to the tax system cause demand for property to wane.

Despite this concern about house prices, Purplebricks continues to move higher and has now recorded share price gains of 45% since the turn of the year. However, the scope for further gains could be somewhat limited. Certainly, there is a major opportunity for web-based estate agencies such as Purplebricks to encroach on traditional estate agency business. But with Purplebricks trading on a forward price-to-earnings (P/E) ratio of around 44, it appears to lack a margin of safety.

With the EU referendum just around the corner, house prices set to fall and interest rates likely to rise over the medium term, such a high valuation may cause investment returns from Purplebricks to disappoint.

Also rising today are shares in Immupharma (LSE: IMM). The drug discovery and development company is up by 9% today and this takes its share price rise to 46% in the last week after it announced that it has made progress with its development of a treatment to fight life-threatening autoimmune disease Lupus. As part of its phase 3 trials, Immupharma has begun dosing Lupus sufferers with its Lupuzor treatment at its first European sites in addition to US sites.

Clearly, this is excellent news for the company’s investors and it shows that sentiment towards a stock can rapidly change. Looking ahead, further updates on Lupuzor are anticipated in the short to medium term and they have the potential to push Immupharma’s share price higher. As such, it may be of further interest to less risk averse investors, although it remains a relatively small and higher risk healthcare play.

Meanwhile, shares in Roxi Petroleum (LSE: RXP) have fallen by over 4% today despite no news flow having been released by the company. Its latest news was a set of rather disappointing results which showed that the oil producer has swung into a loss in its most recent financial year. In fact, following a $20m pretax profit in 2014, Roxi Petroleum recorded a near-$2m loss in 2015. That was due in part to the lack of a reversed impairment from 2014 which was not repeated in 2015. However, the fact that Roxi Petroleum avoided impairments at all in 2015 was a positive result for its investors.

Looking ahead, Roxi Petroleum is aiming to increase production in the current year. Furthermore, it is intent on taking advantage of lower costs to develop its BNG asset and it therefore has long term growth potential for less risk averse investors. However, with there being a number of other oil and gas stocks which are profitable and priced to sell, there may be better options elsewhere.

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Peter Stephens has no position in any shares mentioned. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.