usepackage{array, booktabs, makecell, tabularx}
usepackage[pdftex]{graphicx}
usepackage{graphicx}
usepackage[export]{adjustbox}
usepackage{subfigure}
usepackage{float}
usepackage[colorlinks,allcolors=blue]{hyperref}
usepackage{amsmath}
setcellgapes{4pt}%parameter for the spacing
usepackage{mdwmath}
usepackage{mdwtab}
usepackage{colortbl}
usepackage{xcolor}
usepackage{multirow}
begin{document}
            begin{table*}[t]
             centering
             caption{Some of the previous DBQ studies in the literature} label{tab:Studies}
             begin{tabular}{lccl}
               &&&\
               rowcolor{gray!20}
               multirow{-2}{*}{textbf{Country}} & multirow{-2}{*}{textbf{DBQ type}} & multirow{-2}{*}{textbf{Year published}} & multirow{-2}{*}{textbf{Resulting factors}}\
                rowcolor{gray!20}
                midrule
                multirow{2}{*}{UKcite{parker1995}}& multirow{3}{*}{....} & multirow{3}{*}{1995} & driving under influence \
                &&& driving while texting\
                bottomrule
             end{tabular}
            end{table*}
end{document}