Table 2 Most distinguishing words co-occurring with NSF, 1995–2006 to 2007–2018.

Number in parentheses denotes ranking over the entire period 1995–2018. Findings based on sentence-level analysis, in (nontitle) sentences that include a direct mention of the NSF (see Materials and Methods for details on pre-whitening of text). Words in bold are the top five words mentioned over the entire time period. “Most distinguishing words” for each period are the top 20 diff scores, where for each word w, the following is calculated for the first time period (P) and the second time period (Q), respectively: diffwP=countwP#sentencesPcountwQsentencesQ, and diffwQ=countwQ#sentencesQcountwPsentencesP.

The 20 words that most distinguish the time periods:
1995–20062007–2018
YearProgram
FiscalBill
BudgetTeacher
AgencyEducation
PercentGrant
ExpensesFund
NecessaryDepartment
MillionStem
FederalTeaching
SecretaryStandards
CarryingInnovation
ProvidedNist
CommitteeInterest
BasicEnergy
ActivityPartnership
EnvironmentalOffice
EpaInstitute
SalaryScholarship
MayTechnology
DirectorBillion