all_year_filter = new OpenLayers.Filter.Comparison({
     Type: ‘~’,
     property: ‘start_date’,
     value: ‘2014’
});

all_filter_strategy = new OpenLayers.Strategy.Filter({filter: all_year_filter});

cluster_strategy = new OpenLayers.Strategy.Cluster({distance: 42, threshold: 2});

strategies:  [all_filter_strategy, cluster_strategy],
styleMap: mapVars.clusterStyleMap

labelFunction: function(feature){
    var count = feature.attributes.count;
    if (count > 0){
        return count;
    }
}

"TypeError: feature.attributes.count is undefined."