options nodate nonumber ps=55 ls=80;

title 'Groundhog Day Predictions (Shadow = 1) --- Logistic Regression';

/*  Data Source:  www.stormfax.com/ghogday.htm  */

data groundhog;
input Year Shadow;
datalines;
1887    1
1888    1
1890    0
1898    1
1900    1
1901    1
1902    0
1903    1
1904    1
1905    1
1906    1
1907    1
1908    1
1909    1
1910    1
1911    1
1912    1
1913    1
1914    1
1915    1
1916    1
1917    1
1918    1
1919    1
1920    1
1921    1
1922    1
1923    1
1924    1
1925    1
1926    1
1927    1
1928    1
1929    1
1930    1
1931    1
1932    1
1933    1
1934    0
1935    1
1936    1
1937    1
1938    1
1939    1
1940    1
1941    1
1942    1
1944    1
1945    1
1946    1
1947    1
1948    1
1949    1
1950    0
1951    1
1952    1
1953    1
1954    1
1955    1
1956    1
1957    1
1958    1
1959    1
1960    1
1961    1
1962    1
1963    1
1964    1
1965    1
1966    1
1967    1
1968    1
1969    1
1970    0
1971    1
1972    1
1973    1
1974    1
1975    0
1976    1
1977    1
1978    1
1979    1
1980    1
1981    1
1982    1
1983    0
1984    1
1985    1
1986    0
1987    1
1988    0
1989    1
1990    0
1991    1
1992    1
1993    1
1994    1
1995    0
1996    1
1997    0
1998    1
1999    0
2000    1
2001    1
2002    1
2003    1
2004    1
2005    1
2006    1
2007    0
2008    1
;


symbol1 value=dot
        interpol=none;

proc gplot;
plot Shadow*Year / vaxis = 0 1;
run;


proc logistic descending;
model Shadow = Year;
output out=predvals predicted=probs;
   /* data set predvals includes predicted values (in a variable named probs) */
run;


symbol2 value=point
        color=blue
        interpol=join;

proc gplot;
plot (Shadow probs)*Year / overlay vaxis = 0 1;
run;