A dedicated empirical model of the lower ionosphere (50 to 150 km) is built on rocket borne radio wave propagation data. The data are from non-auroral latitudes and "normal" conditions otherwise. Below 70 km in addition Langmuir probe data extend the altitude coverage. Each measured electron density value is compared to its corresponding model value and the deviation (factor) is plotted against time ranging from 1947 to 2004. In the large scatter an increase of about 1% per year can be seen between 75 and 95 km, whereas above 95 km a decrease of similar order seems to prevail. Above 125 km the electron densities increase again appreciably.