The S&P/ASX 200 (Index: ^AXJO) (ASX:XJO) has drifted lower throughout today’s session as investors continue to digest a large number of earnings results.

The main index was trading 0.3% lower at the time of writing, with the consumer staples and industrial sectors the only sectors in positive territory.

Four shares that have performed terribly today, include:

APN Outdoor Group Ltd (ASX: APO)

APN Outdoor has been far and away the worst performing stock on the ASX200 today following an unexpected profit downgrade. The shares of the outdoor advertising company plunged more than 35% at the open following the release of its first half earnings. Despite reporting a 46% increase in first half earnings per share, APN told the market that it expects full year EBITDA to be in the range of $79 million to $84 million, compared to previous guidance of $84 million to $89 million. The company blamed the downgrade on a significant reduction in market activity as a result of the extended Federal election campaign and the Olympics.

oOh!Media Ltd (ASX: OML)

The unexpected profit downgrade from APN outdoor has, unsurprisingly, had a negative impact on the entire outdoor advertising sector and this has seen the shares of oOh!Media crash by around 15% today. Investors should note that the sector has enjoyed an extremely strong run over the past year or so and it could be argued that oOh!Media and APN Outdoor were both priced to perfection. Prior to today’s share price declines, oOh!Media and APN Outdoor were trading on price-to-earnings ratio’s of 35 and 33, respectively. Any negative news, therefore, was also going to have a dramatic impact on their share prices.

NIB Holdings Limited (ASX: NHF)

Shares of the private health insurer have dropped more than 6.2% today following the release of its full year results. Despite reporting an increase in gross margins and a 22.5% increase in earnings per share, NIB warned that it would struggle to replicate its strong performance in FY17 due to increasing competition and premiums becoming less affordable for consumers. Investors have reacted unfavourably to this outlook as it is means NIB will potentially have to discount some of its products in an attempt to gain market share and this will put pressure on margins. Nevertheless, the company is still forecasting for slight growth in FY17 and expects statutory operating profit of between $122 million to $132 million.

Japara Healthcare Ltd (ASX: JHC)

Shares of Japara Healthcare have plunged more than 8.5% today after releasing weaker-than-expected full year results. The aged care operator delivered revenue growth of 16.4% to $327.3 million but was only able to increase net profit after tax (NPAT) by 5.6% to $30.4 million. As highlighted here, investors may have also been disappointed with Japara’s outlook which highlighted the potential for further government funding cuts. Japara shares are now down by around 30% from their 52-week highs, although investor support for the entire aged care sector has taken a beating over the past 12 months.

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Motley Fool contributor Christopher Georges has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. 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. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.