Proceeding pursuant to CPLR article 78 to review a determination of the Nassau County Public Employment Relations Board (NCPERB), dated April 5, 1977, which, after a hearing, denied an application for certification as collective bargaining agent for certain employees and for decertification of the Nassau County Civil Service Employees Association (NCCSEA) as the bargaining agent for such employees. Determination confirmed and proceeding dismissed on the merits, with one bill of costs payable jointly to respondents appearing separately and filing separate *671briefs. Petitioner contends that the determination of the NCPERB denying its application for certification and for decertification of the NCCSEA is arbitrary and capricious because the New York State Public Employment Relations Board would have granted the application: Petitioner’s assertion is based on mere speculation and is highly unlikely, considering that an identical determination made by NCPERB in 1975 was reviewed and affirmed by the State board (see Matter of Nassau County Correction Ofñcers Assn., 8 PERB 3120). An appellate court cannot substitute its judgment for that of an administrative agency and is limited in its review to determining whether the decision is based on substantial evidence or is arbitrary or capricious (Matter of Pell v Board of Educ., 34 NY2d 222). The determination of the NCPERB is neither arbitrary nor capricious and is based on substantial evidence. It must therefore be confirmed. Damiani, J. P., Titone, Rabin and Gulotta, JJ., concur.