table of contents other equity method investments infraservs . we hold indirect ownership interests in several german infraserv groups that own and develop industrial parks and provide on-site general and administrative support to tenants . our ownership interest in the equity investments in infraserv affiliates are as follows : as of december 31 , 2017 ( in percentages ) infraserv gmbh & co . gendorf kg ( 1 ) ................................................................................................... . 39 .
what was the percentage change in the research and development costs from 2015 to 2016
infraserv gmbh & co . knapsack kg ( 1 ) ................................................................................................ . 27 ______________________________ ( 1 ) see note 29 - subsequent events in the accompanying consolidated financial statements for further information . research and development our business models leverage innovation and conduct research and development activities to develop new , and optimize existing , production technologies , as well as to develop commercially viable new products and applications . research and development expense was $ 72 million , $ 78 million and $ 119 million for the years ended december 31 , 2017 , 2016 and 2015 , respectively . we consider the amounts spent during each of the last three fiscal years on research and development activities to be sufficient to execute our current strategic initiatives . intellectual property we attach importance to protecting our intellectual property , including safeguarding our confidential information and through our patents , trademarks and copyrights , in order to preserve our investment in research and development , manufacturing and marketing . patents may cover processes , equipment , products , intermediate products and product uses . we also seek to register trademarks as a means of protecting the brand names of our company and products . patents . in most industrial countries , patent protection exists for new substances and formulations , as well as for certain unique applications and production processes . however , we do business in regions of the world where intellectual property protection may be limited and difficult to enforce . confidential information . we maintain stringent information security policies and procedures wherever we do business . such information security policies and procedures include data encryption , controls over the disclosure and safekeeping of confidential information and trade secrets , as well as employee awareness training . trademarks . amcel ae , aoplus ae , ateva ae , avicor ae , celanese ae , celanex ae , celcon ae , celfx ae , celstran ae , celvolit ae , clarifoil ae , dur- o-set ae , ecomid ae , ecovae ae , forflex ae , forprene ae , frianyl ae , fortron ae , ghr ae , gumfit ae , gur ae , hostaform ae , laprene ae , metalx ae , mowilith ae , mt ae , nilamid ae , nivionplast ae , nutrinova ae , nylfor ae , pibiflex ae , pibifor ae , pibiter ae , polifor ae , resyn ae , riteflex ae , slidex ae , sofprene ae , sofpur ae , sunett ae , talcoprene ae , tecnoprene ae , thermx ae , tufcor ae , vantage ae , vectra ae , vinac ae , vinamul ae , vitaldose ae , zenite ae and certain other branded products and services named in this document are registered or reserved trademarks or service marks owned or licensed by celanese . the foregoing is not intended to be an exhaustive or comprehensive list of all registered or reserved trademarks and service marks owned or licensed by celanese . fortron ae is a registered trademark of fortron industries llc . hostaform ae is a registered trademark of hoechst gmbh . mowilith ae and nilamid ae are registered trademarks of celanese in most european countries . we monitor competitive developments and defend against infringements on our intellectual property rights . neither celanese nor any particular business segment is materially dependent upon any one patent , trademark , copyright or trade secret . environmental and other regulation matters pertaining to environmental and other regulations are discussed in item 1a . risk factors , as well as note 2 - summary of accounting policies , note 16 - environmental and note 24 - commitments and contingencies in the accompanying consolidated financial statements. .