Penn, W.S., Arnay, O.P., Clewett, R.L., Cole, R.H., Dowd, L.P., Enfeur, P., Fisk, G., Gross, A., Grubb, K.A., Hand, R.J., Hollander, S.C., Kelley, E.J., Kelley, W.T., Lazer, W., Mccusker, J.K., Meissner, F., Meyer, R.E., Petit, T.A., Rathmell, J.M., Rennick, D., Saunders, J.E., Savage, J.K., Shaw, S.J., Smolan, M., Thek, R.R., Uleman, T., Wright, J.S., 1959. Marketing Research 23.. https://doi.org/10.1177/002224295902300312