Holographic polymer-dispersed liquid crystals are materials used to make switchable holograms exhibiting electrically controllable diffraction efficiency. Such devices form the building blocks for several applications in displays and telecommunications. Several demanding requirements are placed on switchable holograms for these applications, such as high diffraction efficiency, wide on/off dynamic range, polarization sensitivity control, low switching voltage and power consumption, high speed, uniformity and reliability, low cost, and manufacturability. One phenomenon affecting overall performance is polymer shrinkage. We focus on the effects of this on polarization dependence, index modulation, and chirp. Experimental and theoretical results are presented.